山口 明

We have been developing a micro superconducting quantum interference device (mu-SQUID) magnetometer for the study of quantum effects in mu m- or nm-sized magnetic materials. In the mu-SQUID magnetometer, the sample is placed on the SQUID loop directly and the flux is detected by the loop itself. The close proximity between the sample and the SQUID loop is of great advantage for highly sensitive detection of magnetization from the tiny magnetic materials. However, the heat release during the operation of the SQUID could cause a great problem in experiments below 1 K because of the close proximity of the SQUID and sample. Here we report a digital circuit for the mu-SQUID magnetometer which can reduce the heat release in the low temperature operation and whose parts are commercially available. The circuit consists of a FPGA-digital board with analog-to-digital and digital-to-analog converters, and an independent pre-amplifier. By using this circuit we succeeded in measuring quantum tunneling of magnetization in the single molecule magnet, Mn12Ph at 0.7 K.

Octanuclear and enneanuclear Ni(II) complexes have been synthesized using a microwave reactor. The octanuclear complex Ni-8 presents a new triply bridging coordination mode for the NO2- ligand.

Josephson critical current I-c between a polycrystalline CeCu2Si2 and Al has been measured for the junctions on a CeCu2Si2 surface. A dominant maximum peak at zero magnetic field is observed in the magnetic field H dependence of I-c, suggesting that the Josephson currents flowing from variously-oriented crystallites of CeCu2Si2 are in phase at H = 0. If CeCu2Si2 is in the d(x2-y2)-wave state, in which the sign of the order parameter changes according to the crystallographic orientation, an s-wave component induced on the surface is considered as a possible origin of the s-wave-like behavior of I-c(H) patterns.

We have carried out measurements of magnetic susceptibility on a single crystal of the heavy fermion compound URu2Si2 under pressure up to 0.7 GPa. The external magnetic fields were applied parallel to a- and c-axes. Hidden order transition at T-0 and first-order phase transition between hidden ordered phase and large-staggered-moment antiferromagnetic phase at T-M are observable in both measurements. Temperature dependence of magnetic susceptibility of a- and c-axes exhibits a kink and a drop at T-0 and T-M, respectively. However, the magnitude of the variation on a-axis at T-0 and T-M were about one tenth of those on c-axis, respectively. We conclude that the HO phase has a similar anisotropy to that of AFM phase.

The Josephson effect between LaPt3Si and Al has been investigated for junctions on the (100) and (001) faces of LaPt3Si single crystals and a polycrystal. In the magnetic-field dependence of the Josephson critical current, the anomaly previously reported for CePt3Si appeared; an oscillating pattern without a dominant maximum peak at zero field was observed for the junction on the (001) face. This cannot be interpreted as the Josephson effect between conventional s-wave superconductors and suggests that the origin of the anomaly lies in the noncentrosymmetric crystal structure.

The organic Heisenberg antiferromagnet m-MPYNN.BF4 has a two-dimensional Kagome lattice of S = 1 dimers with a small trigonal distortion. This antiferromagnet indicates a nonmagnetic ground state with a gap of 0.2 K in zero field. To investigate the ground state of this quantum magnet, we measured the AC susceptibility and the magnetization as a function of the magnetic field. Magnetization plateaus in applied fields were sensitively observed from steep decrements in the AC susceptibility at low temperatures. They indicate characteristic behaviors to be expanded at finite temperatures. The magnetization curve indicates that the fractional plateaus are at 1/2 and 3/4 of the saturation magnetization. The observed plateaus are not commensurate with the unit cell of the Kagome lattice, suggesting a contribution of long-distance interactions.

Systematic observations of the magnetically generated fountain pressure in the superfluid He-3 A(1) have been carried out in a newly built apparatus designed to reduce the effect of thermal gradients. In the same apparatus, mechanical pumping and filtering of polarized nuclear spins were realized by the pneumatic pumping action of an electrostatically actuated membrane. In both experiments, the measured induced pressure was observed to decay at all temperatures where the A(1) phase appeared in magnetic fields up to 13 T and liquid pressures between 1 and 29 bar. The inferred spin-relaxation rate tended to increase as the low-temperature phase boundary with the A(2) phase (T-C2) was approached. The increase in spin-relaxation rate near T-C2 can be explained by the presence of a minority spin condensate in the A(1) phase as predicted by Monien and Tewordt and by the application of the Leggett-Takagi theory of spin relaxation in superfluid He-3.

One issue with the micro-superconducting quantum interference device (micro-SQUID) magnetometer system is the magnetic flux detected by the SQUID loop cannot be converted to sample magnetization. Herein we present a technique for absolute quantification of magnetization of a microcrystal sample using a micro-SQUID magnetometer. The field dependence of the magnetic flux from a microcrystal of a known molecular ferromagnet, RbMn[Fe(CN)(6)], was measured. Then, by combining the experimental data and a simple dipole approximation calculation, a highly accurate molar effective magnetic moment was obtained.

We report development of micro superconducting quantum interference device (μ-SQUID) magnetometers for investigation of quantum tunneling of magnetization in μm- and nm-size magnetic materials. Both high- and low-temperature superconductor (HTS and LTS) based μ-SQUID magnetometers were fabricated and a three dimensional magnetic coil system was constructed for this purpose. The HTS-μ-SQUIDs with a hole of 4×9 μm 2 work at temperatures between 4.2 and 70 K and in magnetic fields up to 120 mT. A magnetization measurement of a ferrimagnetic micro-crystal was carried out at 35 K with an accuracy of 10 -9 emu. The development of LTS-μ-SQUIDs has been started in order to study much smaller magnetic materials in a mK temperature range. We present a preliminary result on the LTS-μ-SQUID with a hole of 1×1 μm 2. The critical current as a function of applied magnetic field shows the SQUID modulation at 4.2 K and up to 30 mT. The heat release associated with the present measurement method is estimated to be on the order of several microwatts. © 2009 Springer Science+Business Media, LLC.

Susceptibility and specific heat measurements have been carried out down to 23 mK on polycrystalline [Cu(3)(titmb)(2)(OCOCH(3))(6)]a <...H(2)O {titmb = 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6 trimethylbenzene} with S=1/2 antiferromagnet on Kagom, lattice. The results show an unexpected ferromagnetic long range ordering at 56 mK. The entropy change from 10 K to 23 mK is much larger than the entropy corresponding to electron spin S=1/2 of Cu(2+). The large excess entropy reduction strongly suggests a novel magnetic ordering of the coupled Cu electron and nuclear spin (I=3/2) system. We propose that a frustrated ground state changes to the complex ferromagnetic ground state with help of the enhanced indirect nuclear spin interaction through the hyperfine interaction.

We measured the complex transverse acoustic impedance in both superfluid He-3 A(1) and A(2) phases. This impedance is sensitive to surface states. In our preliminary results, the temperature dependence of the impedance in the A(1) phase is similar to that in A phase, and the imaginary part shows an anomaly in the A(2) phase. These anomalies occurred at the temperature defined as T-k, which is lower as the frequency gets higher. The similar frequency dependence of T-k in each phase suggests that the anomaly is attributed to the same origin. The frequency dependence of the T-k/T-c indicates that the shape of the surface density of each spin pair state did not greatly change in the present experimental temperature range.

Mechanical pumping and filtering of spin-polarized condensate were realized in the superfluid He-3 A(1) phase by the pneumatic pumping action of an electrostatically actuated diaphragm. Spin pumping increased the net spin polarization by 20-50 % as measured by the induced pressure change during spin pumping. The observed spin relaxation time was consistent with the increased spin polarization. These observations demonstrate the feasibility of using spin pumping to substantially increase the effective magnetic field to which the A(1) phase is exposed.

We have developed a high temperature superconductor (HTS) micro SQUID magnetometer for molecular-based magnets. By employing the dipole approximation, we verified the flux value of 40 Phi(0) from the saturation magnetic moment of the ferrimagnetic microcrystal of [Mn(2)(H(2)O)(2)(CH(3)COO)][W(CN)(8)]center dot 2H(2)O (15 x 15 x 13 mu m). Considering the relative arrangement of the sample and the SQUID loop, including the influence of the film and grease, the calculated the flux values were Phi = 71 Phi(0) and 31 Phi(0) at distances of 20 and 30 mu m between the sample bottom face and the SQUID plane, respectively. Thus, the experimentally obtained flux value is reasonable. (C) 2008 Elsevier Ltd. All rights reserved.

He-3 film adsorbed on a graphite surface offers an ideal two-dimensional antiferromagnetic S=1/2 quantum spin system on a triangular lattice. In addition, competition between various multiple spin exchange interactions makes it strongly frustrated. The ground state in such a frustrated quantum spin system is one of the most interesting issues in condensed matter physics. Recent experiments on the antiferromagnetic solid He-3 in the second layer indicate the ground state is a spin liquid, whereas there still exists a controversy on whether or not the spin gap is finite. Here we report the first precise magnetization measurement below 1 mK over the wide magnetic field range up to 11 T. The magnetization curve is found to show a plateau at half of the saturation magnetization, being followed by the full saturation at the unexpectedly high field of around 10 T.

Two dimensional anti-ferromagnetic solid (3)He adsorbed on graphite, so called 4/7 phase, is a strongly frustrated quantum spin system and the ground state is considered to be a gapless spin liquid. To clarify the magnetic behavior, the magnetization curve has been investigated below 1 mK in high magnetic fields, using NMR over the wide frequency region up to 360 MHz. The magnetization is found to reach full saturation at around 10 T.

The magnetic fountain effect occurring in superfluid He-3 A(1) phase is a unique phenomenon in which the pressure and magnetic field gradients in the chemical potential are balanced. The effect has been applied extensively to investigate the intrinsic spin relaxation. We constructed a new improved sample cell. The new cell includes an inner detector and an outer reservoir chamber made of Macor which was helpful to reduce the heat release possibly arising from proton nuclei under high magnetic fields. The measured temperature difference between the two chambers was cut to less than 5 mu K. The measured relaxation time tau of the fountain pressure decreases monotonically and smoothly as the temperature is decreased from T-c1 (normal-A(1) boundary) towards T-c2 (A(1)-A(2) boundary). As the temperature approaches T-c2, tau tends to vanish smoothly.

Continuous-wave NMR measurements were performed for liquid (3)He in porous alumina discs, which have many small pores of 200 nm in nominal diameter regularly aligned in the same direction. The experimental cell is composed of a stack of 85 anopore discs with C-shaped disc spacers between them. The spacers make the sample space well defined and make it easier to discriminate between liquid NMR signals from different spaces. To eliminate solid (3)He layer adsorbed on the aluminas surface, 4 atomic layers of (4)He were pre-coated on the surface in the experimental cell. Experiments were made at pressure of 17.9 bar and temperatures down to about 0.5 mK. The obtained NMR signals are composed of two contributions below superfluid transition temperatures. One seems to come from the liquid inside pores and the other between each anopore discs.

A high-temperature-superconductor-type micrometer-sized dc-SQUID (SQUID denotes superconducting quantum interference divice) magnetometer with much higher sensitivity than a commercial system has been developed. Several kinds of YBa(2)Cu(3)O(7-delta) micro-SQUIDs were fabricated with photolithography techniques to have a hole of 4x9 mu m(2) and 2-mu m-wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the voltage modulation was observed for three different field directions. (c) 2008 American Institute of Physics.

We have developed a high temperature superconductor (HTS) micrometer-sized dc superconducting quantum interference device (SQUID) magnetometer for high field and high temperature operation. It was fabricated from YBa(2)Cu(3)O(7-delta) of 92 nm in thickness with photolithography techniques to have a hole of 4 x 9 mu m(2) and 2 mu m wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the modulation patterns of critical current I(c) were observed for three different field directions. They were successfully used to measure the magnetic properties of a molecular ferrimagnetic microcrystal (23 x 17 x 13 mu m(3)), [Mn(2)(H(2)O)(2)(CH(3)COO)][W(CN)(8)]center dot 2H(2)O. The magnetization curve was obtained in magnetic field up to 0.12 T between 30 and 70 K. This is the first to measure the anisotropy of hysteresis curve in the field above 0.1 T with an accuracy of 10(-12) J T(-1) (10(-9) emu) with a HTS micro-SQUID magnetometer. (C) 2008 American Institute of Physics.

Two dimensional anti-ferromagnetic solid He-3 on graphite in the so called 4/7 phase is a highly frustrated quantum spin system and its ground state is considered to be a gapless spin liquid. To investigate the detailed magnetic behavior, the magnetization curve has been measured below 1 mK in high magnetic fields, by use of NMR over a wide frequency range up to 84 MHz. The magnetization of the 4/7 phase seems to have a plateau at half the saturation magnetization, which is not inconsistent with results obtained with a double gradient Faraday magnetometer.

Continuous-wave NMR measurements were performed for liquid He-3 in porous alumina with nominal pore size of 20 nm in diameter, at temperatures down to 0.3 mK. The signal is composed of two contributions: from the liquid and from the boundary solid layer of He-3 on the alumina's surface. The latter shows a well-known ferromagnetic tendency and signal intensities can be fitted to a Curie-Weiss law in the high temperature region. The obtained Weiss temperatures are 0.18 and 0.50 mK at 7.5 and 28 bar, respectively. He-4 coverage (4 monolayers) completely eliminates boundary signal between 7.5 bar and 32.5 bar. The residual liquid signal shows frequency shift and broadening below superfluid transition temperatures depending on liquid pressures. The obtained P-T phase diagram well resembles that of bulk liquid He-3 in spite of the very narrow pore-size comparable to the coherence length of superfluid He-3.

A fountain effect is a common phenomenon in both He-3 and He-4 superfluids. Unique to superfluid He-3 is the magnetic fountain effect, which has been used to determine the spin direction of the condensate in He-3 A(1) phase. Here we present a pressure driven fountain effect in A(1) phase. The experimental cell is composed of a large reservoir connected to a small detector chamber through superleak channels of width of 20 mu m. One wall of the detector chamber houses a movable circular 6 mu m thick membrane which serves as a sensitive capacitive pressure sensor and also acts as a spin pump. In A(1) phase, a DC voltage applied on the capacitor induces a simultaneous mass and spin superfluid current into the small chamber. After equilibration, removal of the DC voltage causes a sudden pressure drop followed by a slow relaxation. The sudden drop is a consequence of reversed superfluid flow through the superleak. The observed decay times during the slow relaxation agree with those obtained in magnetically induced spin flow experiment. These observations show that the slow relaxation stems from spin relaxation in the absence of applied field gradient.

Two-dimensional anti-ferromagnetic solid He-3 on graphite, so called 4/7 phase, is a highly frustrated magnetic system and its ground state is considered to be a gapless spin liquid. Then how is the behavior in high magnetic fields? We tried to observe the magnetization curve at around 1 mK in high magnetic fields up to 10 T, using a Faraday-type magnetometer. To eliminate a large background signal from graphite as a substrate and copper as a thermal link, a double gradient coil system is employed to produce opposite field gradients in two regions equidistant from the field center. Preliminary results of the 4/7 phase on graphite show no saturated magnetization even at 1 mK and 10 T, suggesting the existence of magnetization plateau.

Nuclear susceptibility of liquid He-3 in Grafoil preplated by a few layers of He-4 has been studied with a cw NMR method at temperatures between 0.7 and 100 mK under various liquid pressures. The 3.5 layers of He-4 preplating suppress the formation of the first three solid He-3 layers, eliminating most of surface magnetization at saturated vapor pressure. However, with increasing liquid pressure, the magnetization obeying a Curie-Weiss law gradually grows in the same way as for pure liquid He-3. This magnetization, induced by pressurization, is attributable to the formation of solid He-3 layer above the preplated He-4. It shows a strong ferromagnetic tendency, probably due to the intralayer exchange interaction.

The magnetic properties of He-3 in its various phases originate from the interactions among the nuclear spins(1). The spin-polarized 'ferromagnetic' superfluid He-3 A(1) phase(2) ( which forms below 3 mK between two transition temperatures, T-c1 and T-c2, in an external magnetic field) serves as a material in which theories of fundamental magnetic processes and macroscopic quantum spin phenomena may be tested. Conventionally, the superfluid component of the A(1) phase is understood(3-6) to contain only the majority spin condensate, having energetically favoured paired spins directed along the external field and no minority spin condensate having paired spins in the opposite direction. Because of difficulties in satisfying both the ultralow temperature and high magnetic field required to produce a substantial phase space, there exist few studies of spin dynamics phenomena that could be used to test the conventional view of the A(1) phase. Here we develop a mechanical spin density detector that operates in the required regime, enabling us to perform measurements of spin relaxation in the A(1) phase as a function of temperature, pressure and magnetic field. Our mechanical spin detector is based in principle on the magnetic fountain effect(7); spin-polarized superfluid motion can be induced both magnetically and mechanically, and we demonstrate the feasibility of increasing spin polarization by a mechanical spin filtering process. In the high temperature range of the A(1) phase near T-c1, the measured spin relaxation time is long, as expected(2,8,9). Unexpectedly, the spin relaxation rate increases rapidly as the temperature is decreased towards T-c2. Our measurements, together with Leggett - Takagi theory(5), demonstrate that a minute presence of minority spin pairs is responsible for this unexpected spin relaxation behaviour. Thus, the long-held conventional view(2) that the A(1) phase contains only the majority spin condensate is inadequate.

A series of Ni-4 cubane complexes with the composition [Ni(hmp)(ROH)Cl](4) complexes 1-4 where R=-CH3 (complex 1), -CH2CH3 (complex 2), -CH2CH2(C4H9) (complex 3), -CH2CH2CH2(C6H11) (complex 4), hmp(-) is the anion of 2-hydroxymethylpyridine, t-Buhmp(-) is the anion of 4-tert-butyl-2-hydroxymethylpyridine, and dmb is 3,3-dimethyl-1-butanol] and [Ni(hmp)(dmb)Br](4) (complex 5) and [Ni(t-Buhmp)(dmb)Cl](4) (complex 6) were prepared. All six complexes were characterized by dc magnetic susceptibility data to be ferromagnetically coupled to give an S = 4 ground state with significant magnetoanisotropy (D approximate to -0.6 cm(-1)). Magnetization hysteresis measurements carried out on single crystals of complexes 1-6 establish the single-molecule magnet (SMM) behavior of these complexes. The exchange bias observed in the magnetization hysteresis loops of complexes 1 and 2 is dramatically decreased to zero in complex 3, where the bulky dmb ligand is employed. Fast tunneling of magnetization is observed for the high-symmetry (S-4 site symmetry) Ni-4 complexes in the crystal of complex 3, and the tunneling rate can even be enhanced by destroying the S-4 site symmetry, as is the case for complex 4, where there are two crystallographically different Ni4 molecules, one with C-2 and the other with C-1 site symmetry. Magnetic ordering temperatures due to intermolecular dipolar and magnetic exchange interactions were determined by means of very low-temperature ac susceptibility measurements; complex 1 orders at 1100 mK, complex 3 at 290 mK, complex 4 at similar to 80 mK, and complex 6 at < 50 mK. This confirms that bulkier ligands correspond to more isolated molecules, and therefore, magnetic ordering occurs at lower temperatures for those complexes with the bulkiest ligands.

Several tetranuclear nickel(II) single-molecule magnets (SMMs) have been prepared with the general composition of [Ni(hmp)(ROH)X](4) S, where hmp(-) is the monoanion of 2-hydroxymethylpyridine, X- is either Cl- or Br- and S is the solvate molecule. Magnetization versus magnetic field hysteresis loops for these Ni-4 SMMs show that there is a relatively fast rate of magnetization tunneling (small coercive field) and, in certain cases, an exchange bias present. Detailed measurements have been carried out in order to determine the origin of the fast magnetization tunneling. High-field electron paramagnetic resonance (HFEPR) data were collected on a single crystal of [Zn(hmp)(dmb)Cl](4) doped with a small amount of Ni(II), where, dmb is 3,3-dimethyl-1-butanol. These variable-frequency/temperature data give values of the single-ion zero-field splitting parameters D-i and E-i, and the orientations of these interactions, for the single Ni-II ions in a Zn3Ni complex doped into a Zn-4 crystal. HFEPR data were also obtained at many frequencies and temperatures for a single crystal of isostructural [Ni(hmp)(dmb)Cl](4). Rotation of the single crystal such that the external field is positioned in the hard plane clearly establishes that the transverse zero-field interaction B-4(4) is the cause of the fast magnetization tunneling in the S = 4 ground state of this SMM. The magnitude of B-4(4) and the Ni-4 D value can be related to the directionality and magnitude of the D-i and E-i interactions at the individual Ni-II ions, determined for the doped crystal. The microenvironments and ligand dynamics were probed by means of a single-crystal X-ray structure at 12 K and by heat capacity data. (c) 2005 Elsevier Ltd. All rights reserved.

A Faraday-type magnetometer has been developed to measure the nuclear magnetization of monolayer He-3 films adsorbed on Grafoil at temperatures down to 0.1 mK under high magnetic fields up to 10 T. The magnetic force is measured capacitively by monitoring the displacement of a wire-suspended copper plate, on which are diffusion-bonded many copper foils sandwiched by Grafoils. To eliminate a large background signal from Grafoil and copper, a double gradient coil system is employed to produce opposite field gradients at two regions the same distance apart from the center. At each region, exfoliated and non-exfoliated graphite foils are put one by one. Some other devices are discussed to improve a signal to noise ratio. (c) 2005 Elsevier Ltd. All rights reserved.

A low-density solid 3 He film adsorbed on graphite surface forms an ideal two-dimensional (2D) quantum spin system with nuclear spin S= 1/2 on a triangular lattice. In the antiferromagnetic region called the 4/7 phase, the existence of the competing higher order multiple spin exchange (MSE) interactions in addition to a geometrical frustration, makes the system strongly frustrated. The ground state has been investigated both theoretically and experimentally, but it is still an open question. The NMR measurements for the 4/7 phase adsorbed on both one layer of 4 He and two layers of HD preplated graphite have been made down to the temperatures of 10 mu K which is by a factor of 10 lower than the previous. The observed susceptibility shows a gradual increase with no abrupt change. This fact strongly suggests that the triangular antiferromagnet with the higher order multiple exchanges has a gapless spin liquid ground state. (c) 2005 Elsevier Ltd. All rights reserved.

We have measured the nuclear susceptibility of He-3 in Grafoil filled with pure liquid He-3 over the pressure region between 0.6 and 31.38 bar and at temperatures down to 0.5 mK with a cw NMR method. The nuclear magnetization corresponding to the adsorbed He-3 layers on the Grafoil surface shows a strong ferromagnetic tendency with a periodic behavior as a function of liquid pressure. This observation is attributable to the growth of third and fourth solid He-3 layer with the liquid pressure increase. The pressure dependence of the Weiss temperature indicates that the third layer is completed at 19 bar and the fourth probably at 28 bar. The results for Grafoil pre-plated by 2.5 and 3.5 layers of He-4 are consistent with this scenario. (c) 2005 Elsevier Ltd. All rights reserved.

To realize helium quantum fluids in clusters and in one-dimensions, we have studied He-4 and He-3 adsorbed in nanometer diameter pores of zeolite and FSM-16. In each cage 13 angstrom in diameter of Na-Y zeolite covered with helium solid layer, a few helium atoms are suggested to be Bose and Fermi clusters for He-4 and He-3 atoms, respectively, of which symmetry difference results in completely different eigenstates and low temperature heat capacities. In the one-dimensional (ID) pores of 18 and 28 angstrom in FSM-16, He-4 fluid nanotubes are formed on the pore walls preplated with solid-like helium layers. Absolute ID Bose fluid is realized at sufficiently low temperatures and appropriate coverages, where the transverse motion in the fluid tube is in a ground state. We observed a temperature-linear term of the heat capacity probably due to the I1D phonon heat capacity of the ID interacting Bose fluids. (c) 2005 Elsevier Ltd. All rights reserved.

Heat capacity measurements have been made down to 5 mK for He-3 fluid films adsorbed in one-dimensional (1D) nanometer-scale pores, 28 Angstrom in diameter, preplated with He-4 of 1.47 atomic layers. At low He-3 density, the heat capacity shows a density-dependent, Schottky-like peak near 150 mK asymptoting to the value corresponding to a 2D Boltzmann gas at high temperatures. The peak behavior is attributed to the crossover from a 2D gas to a 1D state at low temperatures. The degenerate state of the 1D He-3 fluid is indicated by a predominantly linear temperature dependence below about 30 mK.

The reaction of 2-(hydroxyethyl)pyridine (hepH) with a 2:1 molar mixture of [Mn3O(O2CMe)(6)(PY)(3)]ClO4 and [Mn3O(O2CMe)(6)(PY)(3)] in MeCN afforded the new mixed-valent (16Mn(III), 2Mn(II)), octadecanuclear complex [Mn18O14(O2CMe)(18)(hep)(4)(hepH)(2)(H2O)(2)](Clo(4))(2) (1) in 20% yield. Complex 1 crystallizes in the triclinic space group P1. Direct current magnetic susceptibility studies in a 1.0 T field in the 5.0-300 K range, and variable-temperature variable-field dc magnetization studies in the 2.0-4.0 K and 2.0-5.0 T ranges were obtained on polycrystalline samples. Fitting of magnetization data established that complex 1 possesses a ground-state spin of S = 13 and D = -0.18 K. This was confirmed by the value of the in-phase ac magnetic susceptibility signal. Below 3 K, the complex exhibits a frequency-dependent drop in the in-phase signal, and a concomitant increase in the out-of-phase signal, consistent with slow magnetization relaxation on the ac time scale. This suggests the complex is a single-molecule magnet (SMM), and this was confirmed by hysteresis loops below 1 K in magnetization versus dc field sweeps on a single crystal. Alternating current and direct current magnetization data were combined to yield an Arrhenius plot from which was obtained the effective barrier (U-eff) for magnetization reversal of 21.3 K. Below 0.2 K, the relaxation becomes temperature-independent, consistent with relaxation only by quantum tunneling of the magnetization (QTM) through the anisotropy barrier via the lowest-energy M-S = +/-13 levels of the S = 13 spin manifold. Complex 1 is thus the SMM with the largest ground-state spin to display QTM.

Measurements of spin relaxation in superfluid He-3-A(1) phase as inferred from the decay of magnetic fountain pressure are reported in magnetic fields up to 8 tesla and in pressure between 1 and 29 bars. Unlike in the previous experiment(1), the magnetic fountain pressure detector is placed in an apparatus containing only A(1) phase liquid and there is no interface with any other phases of He-3. An abrupt large change in relaxation time observed in the previous experiment is now absent near the middle of A(1) phase. This observation supports the idea that the origin of the abrupt change in relaxation time is the presence of A(1)/A(2) interface.

The reaction of 1/3 equivalent of CuCl2.2H2O with MnCl2.4H(2)O and 5-bromo-2-salicylideneamino-1-propanol (H(2)5-Br-sap) in methanol gave dark brown crystals of [(MnCuCl)-Cu-III-Cl-II(5-Br-sap)(2)(MeOH)] (1). Complex 1 has an alkoxo-bridged dinuclear core of Mn-III and Cu-II ions, which have elongated octahedral and square-planar coordination geometries, respectively. In dc magnetic susceptibility measurements, chi(m)T values increased as the temperature was lowered, followed by a sudden decrease below 20 K. This behavior is indicative of the occurrence of intramolecular ferromagnetic interactions, and fitting gave an S=5/2 spin ground state with an exchange coupling constant J(MnCu) of + 78 cm(-1). Magnetization data collected as a function of temperature and applied magnetic field were analyzed by using a spin Hamiltonian with isotropic Zeeman and axial zero-field splitting (ZFS) terms, and a negative D-5/2 value (-1.86 cm(-1)) was obtained. A high-field EPR (HFEPR) spectrum (342.0 GHz) at 4.2 K was composed of four peaks, and two additional peaks at higher magnetic field appeared as the temperature was increased. The temperature dependences in the HFEPR spectra are indicative of a negative D-5/2 value, and fitting of the data gave D-5/2 = -1.81 cm(-1). In the ac magnetic susceptibility measurements, frequency dependent in-phase (chi(m)') and out-of-phase (chi(m)") signals with peak maxima at 0.7-1.5 K were observed and small peaks below 0.7 K appeared. The ac susceptibility data supports that 1 is a single-molecule magnet (SMM). Arrhenius plots for the chi(m)" peaks from 0.7-1.5 K gave the re-orientation energy barrier (DeltaE) of 10.5 K with a pre-exponential factor of 8.2 x 10(-8) s.

We have measured the heat capacity of He-3 adsorbed on one-dimensional (1D) nanopores of FSM-16 with different pore-diameters. Dilute He-3 atoms on more than one layers of He-4 preplated nanotunnels with 22 angstrom in diameter show a Schottky-type peak around 0.25 K, which is similar to our recent report for 28 angstrom nanotunnels. This behavior of heat capacity is explained as the crossover from 1D to 2D motion of Fermi gas in a confined geometry. The pore-size effect on the temperature and magnitude of the peak is quanlitatively reproduced by a simple calculation for non-interacting Fermi gas in the adsorption potential from the substrate.

The nuclear susceptibility of liquid He-3 in Grafoil pre-plated by 2.5 and 3.5 layers of He-4 has been studied with a cw NMR method at temperatures between 0.7 and 100 mK under various liquid pressures. The 3.5 layers of He-4 pre-plating suppresses a formation of the first and second solid He-3 layer, eliminating most of surface magnetization at saturated vapor pressure. However, with increasing liquid pressure, a magnetization obeying a Curie Weiss law gradually grows in the same way as in the previous experiment for pure liquid He-3. This magnetization, induced by pressurization, is attributable to the formation of solid He-3 layer above the pre-plated He-4.

A degenerate Fermi fluid has been realized recently for He-3 films adsorbed in one-dimensional (1D) pores 28 angstrom in diameter, preplated with He-4 layers. In order to study the influence of the He-4 or preplating on the He-3 Fermi fluids. heat capacity was measured down to 4 mK for two preplated He-4 films of different thickness. At low temperatures, no substantial difference was found between the two cases. On the other hand, a large difference appeared above about 150 mK. The large He-3 heat capacity for the thick He-4 preplating suggests thermal excitation, of the He-3 atoms to the excited energy levels of the Andreev states in the He-4 fluid layers.

A Faraday-type magnetometer has been developed to measure the nuclear magnetization of monolayer He-3 films adsorbed on Grafoil at temperatures down to 0.1 mK under high magnetic fields up to 10 T. The magnetic force is measured capacitively by monitoring the displacement of a wire-suspended copper plate. A double gradient coil system is employed to produce opposite field gradients at two regions the same distance apart from, the center. At each region, exfoliated and non-exfoliated graphite foils are put one by one to eliminate a large background signal from Grafoil and copper.

We have measured the nuclear susceptibility of He-3 in Grafoil filled with pure liquid He-3 over the pressure region between 0.6 and 31.38 bars and at temperatures down to 0.5 mK with a cw NMR method. The nuclear magnetization corresponding to the adsorbed He-3 layers on the Grafoil surface shows a strong ferromagnetic tendency with a periodic behavior as a function of liquid pressure. This observation is attributable to the growth of third and fourth solid He-3 layers with the liquid pressure increase. The pressure dependence of the Weiss temperature indicates the third layer is completed at 19 bars and the fourth probably at 28 bars. The number of localized spins estimated from the solid magnetization is almost doubled from 0 to 28 bars, being consistent with this scenario.

We report the magnetic susceptibility of He-3 in Grafoil filled with pure liquid He-3 at 27.6 bar and at temperatures down to 0.1 mK with a cw NMR method. It is composed of two contributions: from the bulk liquid and from the adsorbed layer of He-3 on the Grafoil surface. The latter shows a well-known strong ferromagnetic tendency and can be fitted to a Curie-Weiss law in the high temperature region. The obtained Weiss temperature is surprisingly large compared with the previous ones.

A He-3 film formed in quite narrow pores is one of the possible model systems for a one-dimensional Fermi fluid. Here we report our new heat capacity results of He-3 and He-4 film adsorbed in a straight pore 28 Angstrom in diameter down to 5 mK. The coverage and temperature dependence of the heat capacity indicates that a fluid phase appears between the second layer promotion and the complete filling of the pores. Since the heat capacity of He-3 adsorbed on the bare substrate shows a large upturn due to the nuclear heat capacity of the localized He-3, it is difficult to observe the true heat capacity of the fluid phase. By replacing the localized He-3, we can successfully suppress the upturn and observe the true heat capacity of the fluid phase.

The negative ion mobility has been measured in superfluid He-3 at pressures above 20 bar under high magnetic field up to 14 Tesla. It does not depend on the temperature in the normal phase, followed by a rapid increase below the superfluid transition in both A(1) and A(2) phase. The isothermal mobility is found to be independent of the magnetic field in the normal and A(2) phase, while it decreases with increasing magnetic field in the A(1) phase. This field dependence is explained by taking account of the field dependence of the transition temperature (T-A1 between the normal and the A(1) phase. Therefore the scattering cross section between the negative ion and the He-3 quasiparticles has no magnetic field dependence both, in the superfluid and the normal phase.

The electron spin density distributions of p-N-alkylpyridinium alpha-nitronyl nitroxides with alkyl = methyl (p-MPYNN) and n-butyl (p-BPYNN) were determined in their iodide salts from the temperature dependence of the solid-state high-resolution H-1 MAS NMR spectra. The results were compared with that of p-pyridyl alpha-nitronyl nitroxide (p-PYNN) to see how positive charge on the aromatic ring affects the spin density distribution. This effect was not significant contrary to the effect of incorporation of a nitrogen atom into the aromatic group. The change in the magnitude of the spin density can be ascribed to the dihedral angle between nitroxide and aromatic moieties. Relatively large hyperfine coupling constant of N-methyl proton, which is almost half as large as those of beta-methyl proton, implies the utility of the N-methyl group as an intermolecular magnetic coupler. (C) 2003 Published by Elsevier Science Ltd.

The synthesis and structural characterization of the two new Mn complexes [Mn18O14(O2CMe)(18)(heP)(4)(hepH)(2)(H2O)(2)](ClO4)(2) (1) and [Mn21O16(O2CMe)(16)(hmp)(6)(hmpH)(2)(pic)(2)(py)(H2O)](ClO4)(4) (3) are presented, together with a detailed study of their magnetic properties. Complex 1 possesses a ground-state spin of S = 13, and the ground-state spin for 3 is estimated to be S = 17/2 or 19/2. Both complexes 1 and 3 are new examples of single-molecule magnets (SMMs), displaying frequency-dependent out-of-phase AC signals, as well as magnetization vs. DC field hysteresis at temperatures below 1 K. Complex 1 straddles the classical/quantum interface by also displaying quantum tunneling of the magnetization (QTM). (C) 2003 Elsevier Science Ltd. All rights reserved.

A new type of heat switch for a nuclear demagnetization refrigerator has been prepared by diffusion bonding of zinc and copper foils. The details of the fabrication and its performance are described. (C) 2003 Elsevier Science B.V. All rights reserved.

The magnetization relaxation in a tetranuclear manganese cluster Mn-4(pdmH) has been investigated with an extraction and a Faraday magnetometer at 0.14-0.75 K. The relaxation curves in the tunneling regime show the "square-root time" dependence for a short time after reversing the magnetization. This fact suggests the hyperfine and inter-cluster dipolar interactions play important roles for the relaxation. (C) 2003 Elsevier Science B.V. All rights reserved.

Positive ion mobility in normal and superfluid He-3 has been measured as a function of external magnetic fields up to 15 T at various pressures. At 20 mK, a monotonic increase of the inverse mobility with increasing the magnetic field has been observed at the pressures above 20 bars. Below around 3.2 mK, both in the normal and in the superfluid phase, the held, dependence above 20 bars is found to exhibit a pressure dependent dip, followed by a big increase. Possible origins for these anomalous behaviors are discussed. (C) 2003 E Elsevier Science B.V. All rights reserved.

The positive ion mobility (mu) in superfluid He-3 has been measured as a function of temperature under high magnetic fields up to 15 T at several pressures. It exhibits a steep increase at both transition temperatures T-A1 and T-A2 The inversed mobility normalized at T-A1 (= mu(T-A1)/mu(T)) is found to follow a field-independent universal curve as a function. of T/TA(1) in the A(1) phase and as a function of T/T-c in the A(2) phase. Here T-c is the zero field transition temperature. The observed behavior and the effect of the pressure is discussed in terms of what we call a "two-fluid model". (C) 2003 Elsevier Science B.V. All rights reserved.

Magnetic-field dependence of positive ion mobility in liquid He-3 has been studied for the superfluid A(1) and A(2), phase. It exhibits an anomalous behavior, which is sensitive to the liquid pressure especially above 20 bar. The behavior is similar to that observed recently in the normal phase at 3.2 mK. This fact indicates that there exists a similar magnetic scattering mechanism between the positive ion and the He-3 quasiparticles in the superfluid phase. (C) 2003 Elsevier Science B.V. All rights reserved.