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The magnetic memory phenomena in a ceramic YBCO superconductor are studied by zero-field-cooled and thermoremanent magnetization after specific cooling protocols. The ceramic YBCO is considered as random Josephson-coupled networks of 0 and π junctions and shows successive phase transitions. The magnetic glass behavior, similar to those of spin-glasses, is observed below the lower transition temperature. The memory effect occurs strongly in an intermediate stop temperature and suppressed with an increased probing field. The results can be understood by the screening effect of the ceramic superconductor with a finite self- inductance.

The hydrostatic pressure response of TC of the bisdiselenazolyl radical ferromagnet 1 up to 5 GPa was investigated by AC magnetic susceptibility measurements using a SQUID magnetometer and a miniature diamond anvil cell. It was found that the ambient pressure value of TC = 17 K could be raised to 21 K at a pressure of 0.9 GPa. The experimental technique is described in detail and the pressure response is compared to that observed in related systems.

The magnetic property and intraparticle structure of the γ phase of Fe2O3 (maghemite) nanoparticles with a diameter (D) of 5.1±0.5 nm were investigated through AC and DC magnetic measurements and powder X-ray diffraction (XRD) measurements at pressures (P) up to 27.7 kbar. Maghemite originally exhibits ferrimagnetic ordering below 918 K, and has an inverse-spinel structure with vacancies. Maghemitenanoparticles studied here consist of acore with structural periodicity and a disordered shell without the periodicity, and core shows superparamagnetism. The DC and AC susceptibilities reveal that the anisotropy energy barrier (ΔE/kB) and the effective value of the core moment decrease against the initial pressure (P≤3.8 kbar), recovering at P≥3.8 kbar. The change of ΔE/kB with P is qualitatively identical with that of the core moment, suggesting a down-and-up fluctuation of the number of Fe3+ ions constituting the core at the pressure threshold of about 4 kbar. This phenomenon was confirmed by the analysis of the XRD measurement using Scherrer’s formula. The core volume decreased for P≤2.5 kbar, whereas at higher pressure the core was restructured. For 2.5≤P≤10.7 kbar, the volume shrinkage of particle hardly occurs. There, ΔE/kB is approximately proportional to the volume associated to the ordered fraction of the nanoparticles as seen from XRD, Vcore. From this dependence it is possible to separate the core/shell contribution to ΔE/kB and estimate core and surface anisotropy constants. As for the structural experiments, similar experimental data have been obtained for D=12.8±3.2 nm as well., This work in Japan was supported by the CREST project of the Japan Science and Technology Agency (JST) and a Grant-in-Aidfor Young Scientists (B) (19750118) from the MEXT of Japan. The work in Zaragoza has been supported by the research grants MAT2007-61621 and CSD2007-00010 from the Ministry of Education. The Aveiro-Zaragoza collaboration has been supported by the Integrated Spanish-Portuguese Action PT2009-0131. N.J.O. Silva acknowledges CSIC for an I3Pcontract and FCT for a Ciencia 2008 contract.

A radical cation salt, BBDTA (= benzo[1,2-d:4,5-d′]bis[1,3,2]dithiazole) · GaCl 4 , has three polymorphs, labeled α, β and γ. The γ-phase shows a ferromagnetic ordering at 7.0 K, and this Curie temperature ( T C ) is eminently high, in contrast to those of the other organic radical ferromagnets. We have investigated the pressure effects on the γ-phase of BBDTA · GaCl 4 through ac magnetic susceptibility measurements under hydrostatic pressure up to 16.2 kbar. The value of T C increases with linear fashion against pressure and exceeds 14 K at 16.2 kbar. By applying further pressure, it may exceed 16 K of the organic ferromagnet, TDAE-C 60 , which has the highest T C in organic materials . However, the real component of the ac susceptibility below T C is remarkably suppressed with increasing pressure and, at around 2 kbar, it decreases down to 3.5% of that at ambient pressure. Those pressure effects might originate from the pressure-induced structural transformation from the ferromagnetic γ-phase to the diamagnetic α- and/or β-phases and the enhancement of the intermolecular interactions in the surviving γ-phase.

We have investigated pressure effects on a dimetallic ferrimagnet [Mn(en)] 3 [Cr(CN) 6 ] 2 · 4H 2 O (en; ethylenediamine) through the magnetic measurements using a diamond anvil cell in the pressure region up to P = 4.7 GPa. This ferrimagnetic compound has an eminent high transition temperature ( T c) of 69 K at ambient pressure in the structurally characterized molecule-based magnet system. Under hydrostatic pressure, T c linearly increases against pressure, and exceeds 130 K at P = 4.7 GPa. The amount of the saturated moment hardly changes in the considered pressure region. This pressure experiment might become a prototype of artificial material control for the high- T c molecule-based magnet.

Angular and temperature dependence of the ESR spectrum of a single crystal of a salt, MEM–[TCNQ] 2 , were measured under uniaxial pressure up to 1 kbar by using a hand-made pressure cell and a conventional ESR instrument in the temperature range of 1.5–300 K. The ESR spectrum is deformed with increasing pressure and the deformed ESR spectrum significantly depends on the temperature and orientation of the crystal. The ESR spectrum at low temperatures is well separated into three absorptions. One of the absorptions seems to result from free spins and the other two absorptions seem to result from spin-pairs.

Bimetallic ferrimagnet [Cr(CN) 6 ][Mn( R )-pnH(H 2 O)]H 2 O with crystallographical chirality of space group P 2 1 2 1 2 1 exhibits a giant third-order harmonic susceptibility at around 38 K. This anomaly appears as precursory magnetic phenomenon of the magnetic ordering. In order to investigate the effect of lattice distortion on this giant nonlinear magnetic response (NLMR) and finally elucidate the correlation between the structural chirality and the giant NLMR, we performed the ac susceptibility measurement for the single crystal in the situation of bringing about lattice distortion along the direction parallel to the a -axis. This giant NLMR was drastically suppressed even by slight strain, whereas the traces could be confirmed in the region up to 3.7 kbar. We conclude that the appearance of the giant NLMR requires crystal chirality well-regulated over the crystal.

Since the observation of porosity in organic–inorganic hybrids there has been a major development in the study of gas sorption and catalysis as they provide novel surfaces in contrast to metals and oxides including silicates. Of major interest is the possibility of trapping fuel gases and toxic fumes. In addition, their applications as sensors have been demonstrated by use of the change in magnetic or optical properties upon sorption and desorption. The latter experiments have been performed ex-situ. Thus, there is a need to understand the properties in-situ, in particular to follow the performance of the materials continuously. Here, the development of an in-situ apparatus to study the magnetism is presented and applied for the partially dehydrated Ni 2 (H 2 O) 4 PM · 2H 2 O, PM = benzene-1,2,4,5-tetracarboxylate with oxygen (O 2 ) and nitric oxide (NO) in the cavities.

We investigated the magnetization of the organic weak-ferromagnet p -NC.C 6 F 4 .CNSSN in the pressure P region up to 16 kbar. The transition temperature T c at ambient pressure is 35.5 K. T c is enhanced with increasing pressure, and reaches 64.5 K at P =16 kbar, which is the highest T c for a genuine organic weak-ferromagnet. On the other hand, the net moment is suppressed by the pressure, and this can be explained with the Dzyaloshinsky–Moriya model.

The continuous variation of magnetic intermolecular interactions has been studied in the pressurized genuine organic ferromagnet, β -phase para -nitrophenyl nitronyl nitroxide ( T c = 0.61 K), in which a pressure-induced ferro- to antiferromagnetic transition was observed under pressure around 6.5 kbar at 0.45 K. The rotation of the radical group C 6 H 4 NO 2 around its symmetrical axis in crystallized molecules is pointed out to be essential to change magnitude and a sign of the dominant exchange interactions, rather than the shrinkage of the lattice parameters under pressure.

Ni 2 (H 2 O) 4 PM·2H 2 O, where PM is benzene-1,2,4,5-tetracarboxylate, forms square-grid layers with Ni—OCO–Ni bridges that are connected to one another by the benzene moiety. It consists of ferromagnetic layers coupled antiferromagnetically to their neighbors with a long-range Neel ordering at 3 K. A critical field of 1300 Oe suffices to reverse all the moments to a ferromagnetic state. On dehydration to Ni 2 (H 2 O) 2 PM the structure is transformed irreversibly to chains connected by benzene and the magnetic behavior is that of a paramagnet with very weak coupling. By the rehydration of the latter to Ni 2 (H 2 O) 2 PM·2H 2 O, the structure hardly changes but the magnetism recovers showing T N at 3 K.

We have investigated the magnetic properties of two-dimensional networked single-molecule magnet, [Mn4(hmp)4Br2(OMe)2(dcn)2]·0.5H2O·2THF (Hmp=2-hydroxymethylpyridine, dcn=dicyanamide, THF=tetrahydrofuran), through the AC susceptibility measurements up to P=15.3 kbar. This compound exhibits superparamagnetic relaxation phenomenon below 3 K, and the blocking temperature (TB) in low frequency limit is estimated to be 2.00 K at ambient pressure. As pressure increases, the TB once decreases and, at around P=3 kbar, it turns to increase. At P=15.3 kbar, the TB reaches 2.27 K. By analyzing the frequency dependence of TB, it has been revealed that a dynamical critical exponent of the power-law fitting shows the change of up and down, and it approaches 2.0 at last. This result suggests that the intercluster magnetic network changes by pressurization and finally a conventional phase transition may be realized.

Superconducting quantum interference device (SQUID) is a powerful tool, which can detect small magnetic signal with high sensitivity, but it is not easy to make use of the SQUID. Especially in the case of the pressure experiment, it is more difficult to utilize the SQUID due to the space limitation of the coil arrangement. We are trying to establish the vibrating coil magnetometer (VCM) using the SQUID, and our attempt started from the imitating of Ishizuka type of VCM. In the development process, we have developed the original method of coil vibration control and real-time phase-detection system. As the performance test, the superconducting transition of lead was observed in some conditions, and the present sensitivity was confirmed to be about 10 −8 emu at earth field.

The effect of pressure on two-dimensional Heisenberg antiferromagnet Cu(HCOO)2·4H2O has been investigated through X-ray diffraction, susceptibility and magnetization curve measurements. The pressurization induces the paramagnetic behavior above 1.4 kbar. The paramagnetic component increases continuously with increasing pressure, and the antiferromagnetic ordering and field-induced phase transition vanish above 2.8 kbar. The X-ray diffraction pattern at 6.6 kbar is not that of Cu(HCOO)2·4H2O but Cu(HCOO)2·2H2O. Therefore, the pressurization induces the crystal structural change from Cu(HCOO)2·4H2O to Cu(HCOO)2·2H2O with dehydration.

Ceramic YBa 2 Cu 3 O 7− δ composed of sub-micron size grains has shown successive phase transitions under zero field. The first transition occurs inside each grain at T c1 and the second transition occurs among the grains at T c2 ( T c1 ). We measured the current–voltage characteristics and estimated the linear and nonlinear resistivity. The linear resistivity remains finite below T c2 . The nonlinear resistivity has a broad peak above T c2 and diminishes continuously toward T c2 with decreasing temperature. These results are in good agreement with the theoretical analysis and suggest that chiral-glass ordering occurs at T c2 .

A new organic ion-radical salt, 3,3′-diethyl-2,2′-thiazolinocyanine-[TCNQ] 2 , is synthesized and the magnetic properties are investigated. The salt is a quasi-one-dimensional antiferromagnet above 10 K. However, the temperature dependence of the spin-susceptibility and ESR spectra suggests that a magnetic phase transition occurs in the salt near 10 K.

We report the transport properties (the electrical resistivity ρ ( T ) in a magnetic field and the thermoelectric power S ( T ) ) on the filled skutterudite antiferromagnet GdRu4P12 ( T N = 22 K ) synthesized under high pressure. A dramatic increase at T N observed in ρ ( T ) and S ( T ) suggests the formation of a superzone gap due to the Fermi surface nesting. The strong field dependence of ρ ( T ) below 60 K is interpreted as a suppress of magnetic fluctuation.

The pressure effects on the magnetic properties are reported for the quantum spin-liquid system Cu 2 (C 5 H 12 N 2 ) 2 Br 4 . Characteristics of the susceptibility and magnetization above 4 kbar are quite different from those below 3 kbar, where the system keeps the gapped singlet spin-liquid state. The pressure-induced antiferromagnetic phase transition drastically occurs between 3 and 4 kbar. The coexistence of antiferromagnetic and singlet spin-liquid states is observed in the system above 4 kbar.

DC magnetization of Dy2Ti2O7 has been measured down to 30 mK . The ice-rule breaking spin flip appearing at H∼0.9 T ( || [1 1 1]) turns into a first-order transition for T K which is most probably of liquid–gas type. T-linear variation of the critical field suggests that the entropy release across the transition remains finite (∼0.5 J / K mol Dy ) down to 0.03 K , confirming the macroscopic degeneracy in the intermediate ‘kagome ice’ state.

We synthesized two compounds, (C 5 H 12 N) 2 CuCl 4 (hereafter BPCC) and (C 5 H 12 N) 2 CuCl 2 Br 2 (hereafter BPCCB), and have performed the crystal-structure analysis, and susceptibility, magnetization and ESR measurements. The experimental results of BPCC are in good agreement with a two-leg ladder model with a strong-dimer-coupling limit. However, the compound, BPCCB, is close to a ladder model with isotropic coupling limit.

Pressure effects on a single chain magnet [Mn 2 (saltmen) 2 Ni(pao) 2 (py) 2 ](ClO 4 ) 2 (saltmen 2− = N , N ′-(1,1,2,2-tetramethylethylene)bis(salicylideneiminate), and pao − =pyridine-2-aldoximate) have been investigated through AC magnetic measurements under pressure ( P ). The slow relaxation of the magnetization depends on pressure. Both the blocking temperature ( T B ) and energy barrier ( Δ ) increase by pressurization, and those enhancements saturate at around P =7 kbar.

Anisotropic pressure effects on the magnetic properties of a spin-Peierls substance, MEM-[TCNQ] 2 , have been investigated through the measurements of susceptibility, magnetization and ESR spectra for single crystals under uniaxial pressure. Though the results for the single crystals are qualitatively similar to those for microcrystals, we have found that the pressure effects for a and c axes are remarkable, compared with those for b -axis reflecting the peculiar crystal structure of the salt.

Dynamical properties of the ceramic YBa 2 Cu 3 O 7− δ have been investigated by magnetic measurements. We measured ac-susceptibilities at various frequency under zero external field and carried out dynamic scaling analysis near inter-grain transition temperature. The results exhibit scaling behavior for the critical exponents zν =8 and β =0.5. These values are fairly close to the ones for the chiral-glass estimated by Monte Carlo simulations.

Proton NMR measurements have been performed to investigate random-bond effects in a spin-ladder system. We synthesized a random-bond ladder Cu2(C5H12N2)2(Cl1−xBrx)4 and measured the temperature dependence of 1 H spin-lattice relaxation time. The spin-gap energy for a random mixture compound is smaller than those for pure systems. The result suggests that the ground state of the random-bond ladder approaches to a gapless state.

La1−xSrxMnO3 nanoparticles were prepared by calcination of a molecular sieve MCM-41 soaked in precursor solution. Magnetic properties have been investigated by the magnetization measurements. Superparamagnetic behavior of the nanoparticles is observed both for the antiferromagnetic and ferromagnetic phases at low temperatures. For the antiferromagnetic phase, the superparamagnetic moment corresponds to the uncompensated moments in the antiferromagnetic particles. While for the superparamagnetism for the ferromagnetic phase is smaller than the superparamagnetism estimated for the single-domain ferromagnetic particles.

An anomalous pressure effect on the magnetic susceptibility of a spin-Peierls substance, MEM-[TCNQ] 2 , is observed. As the pressure increases, the susceptibility at low temperatures increases as if free magnetic spins are produced and it overwhelms the spin-Peierls transition. In order to clarify the pressure effect, the crystal structure of the substance under pressure has been studied by using synchrotron radiation X-rays. The reflection resulting from the superlattice of the spin-Peierls state below 18 K disappears under pressure and the crystal structure is significantly affected even at room temperature.

Ceramic high- T C superconductors may be viewed as a weakly coupled random Josephson network containing the so-called π-junctions, and a chiral-glass transition is predicted to be occurred in such d-wave ceramics. In the present work, pressure dependence of the chiral-glass transition have been investigated on YBa 2 Cu 3 O 7− y and YBa 2 Cu 4 O 8 ceramics. With decreasing temperature, a superconducting order occurs at first inside each grain at T C1 and furthermore among the grains at T C2 ( T C1 ). The T C2 increases with increase of pressure, while the sharpness of the transition at T C2 does not change. In spite of differences in not only T C2 ’s but also T C1 ’s, the increasing rates of T C2 by pressure are nearly the same.

In the randomly diluted magnet Ni x Mg 1− x (OH) 2 , the broad line caused by the antiferromagnetically ordered spins is observed at the proton NMR spectrum. The broad line remains even at higher temperature than Neel point T N . This result strongly suggests the existence of the Griffiths phase.

From new magnetization measurements and our previous thermal analysis on the first genuine organic ferromagnet, β-phase para-nitrophenyl nitronyl nitroxide (T c =0.6 K ) , found in 1991, we have evaluated the variation of some dominant exchange interactions in this magnetic system in the course of a pressure-induced ferro- to antiferromagnetic transition (T c =0.45 K , P c =6.5 kbar ) .

The compound Cu 2 (C 5 H 12 N 2 ) 2 Br 4 (CHpB) is isostructural with a typical spin-ladder material Cu 2 (C 5 H 12 N 2 ) 2 Cl 4 (CHpC). The susceptibility and magnetization of CHpB show spin-gap behavior at low temperatures as observed in CHpC. The results are in good agreement with a spin-ladder model.

ESR measurements have been performed in high magnetic fields up to 30 T on the spin-Peierls compounds CuGeO3 and MEM(TCNQ)2 to examine the magnetic excitation in the magnetic phase (M phase) induced by external fields. Discontinuous changes in the resonance fields have been observed around the phase boundary between the dimerized spin-Peierls phase and the M phase for both CuGeO3 and MEM(TCNQ)2. Anisotropic AFMR modes are observed in the M phase of CuGeO3.

Static and dynamic properties of a diluted quasi-two-dimensional magnet Ni x Mg 1 − x (OH) 2 have been investigated by the measurements of susceptibility and magnetization. The irreversible magnetization and its slow-relaxation phenomena are observed even above the Neel temperature of the diluted magnet. The experimental results suggest the existence of the Griffiths phase in Ni x Mg 1 − x (OH) 2 .

In a one-dimensional compound (CH 3 ) 4 NCo(NO 2 ) 3 , which has the same crystal structure as (CH 3 ) 4 NNi(NO 2 ) 3 , we have found that next-nearest neighbor exchange interactions exist to frustrate the nearest neighbor interactions. A little larger Haldane gap energy obtained in the Ni 2+ compound is suggested to be due to this kind of frustration.

The static magnetic susceptibility of high-quality single-crystalline Bi 2 Sr 2 CaCu 2 O 8+δ has been investigated form 50 K up to 350 K with particular interest in the anisotropic behavior. Above the superconducting transition a large diamagnetic contribution to χ ⊥ . is observed as temperature approaches T c , whereas this contribution to χ // II is found to be much less significant. This result is attributed to the superconducting fluctuations in this two-dimensional system. Above about 150 K, the susceptibility is nearly temperature independent.

The spin correlation of the salt MEQSeC-[TCNQ] 2 is temperature dependent. The spin system changes from pair like ( T