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We have performed the detailed measurements of temperature dependence of magnetization M ( T ) on MgB 2 single crystals in a wide range of field H using torque magnetometry. In a field region, where the peak effect in M ( H ) is observed, we find that M ( T ) of the warming branch increases monotonously with T and exhibits a small step-like increase at T 1 ∗ , which is related to the order–disorder transition, while M ( T ) of the cooling branch, showing the larger values than that in warming branch below T 1 ∗ , drops suddenly toward the warming branch at T 2 ∗ . We ascribe this anomalous behavior of M ( T ) of the cooling branch to a supercooling phenomenon of disordered phase, which transforms to the ordered state at T 2 ∗ .

We have studied the order–disorder transition in high quality MgB 2 single crystals, using a torque magnetometry combined with a ‘vortex shaking’ technique. In the wide range of temperature T , field H and the H direction, we succeed in obtaining reversible magnetization curves M rev ( T , H ) by shaking the pinned vortices. Especially at low temperatures below 25 K and high fields, where the irreversible magnetization curve exhibits the peak effect due to the order–disorder transition, it is found that the peak is transformed into the clear step in M rev ( H ). Similar step-like behavior is also observed in the temperature dependence of magnetization M rev ( T ). These results give direct evidence that the order–disorder transition, which is hidden by the large hysteresis of magnetization, has the nature of first-order transition.

In the filled skutterudite compounds (RT 4 X 12 : R rare earth, T=Fe, Ru, Os, and X=pnictogen-ions), various attractive features have been found by replacing the constituent elements, e.g., metal–insulator transition in PrRu 4 P 12 , competing heavy fermion and multipolar ordered states in PrFe 4 P 12 , heavy fermion superconductivity in PrOs 4 Sb 12 , etc. Most of these features are realized probably by the unique crystal structure; R is embedded in the cage made of 12X and eight T ions, so that the strong c–f hybridization becomes a common feature irrespective of the constituent elements. The strong c–f hybridization in skutterudites enables the strongly correlated electron behaviors even in the systems containing rare-earth elements with more than one 4f-electron. The effect of X-replacement appears most apparently as a change in c–f hybridization, as is naturally inferred from the large difference in lattice constant. In addition to the c–f hybridization effect, it was recognized that f-electron's multipolar degrees of freedom and relatively small crystalline electric field splitting are important factors to understand the aforementioned novel phenomena.

We present the temperature--pressure--magnetic-field phase diagram of the itinerant-electron metamagnet UCoAl determined from the ac susceptibility measurement. The quantum critical point (QCP) was found to be located at $2.9\ifmmode\pm\else\textpm\fi{}0.2$ GPa ($\ensuremath{\equiv}{P}_{\mathrm{QCP}}$) and $130\ifmmode\pm\else\textpm\fi{}5$ kOe. In addition to the determination of the phase diagram, we report magnetic and transport properties in the paramagnetic state and around the phase boundary. The critical divergence of the magnetic susceptibility is suppressed toward the QCP. From the longitudinal magnetoresistance and the resistivity under magnetic fields, enhancement of the resistivity is observed in the so-called supercritical region. In the paramagnetic region, the magnetoresistance and temperature dependence of the resistivity exhibit complex behaviors, especially in the vicinity of 1.5 GPa and ${P}_{\mathrm{QCP}}$.

The field dependence of anisotropy in the mixed state of MgB 2 single crystals is studied using torque magnetometry. At all temperatures measured, the anisotropy parameter γ , derived from the angular dependence of magnetic torque τ , increases with increasing field H and shows a plateau with a almost constant value of ∼4.5, indicating that the isotropic π band contribution to the superconductivity weakens with H and only the anisotropic σ band contribution remains in the plateau region. In the low field region below the plateau, we found a change in the functional form of γ ( H ) at H = H * . In addition, the step-like decrease in the H dependence of d( τ / H )/d H is observed at H * . These anomalies can be related to the change in the vortex lattice structure accompanied by the decrease of the π band contribution.

A general survey of the variety of phenomena exhibited by the filled skutterudite compounds is presented from the view points of electrical properties and electronic structure, putting emphasis on the Pr- and Sm-based ones. Until now, Pr-based ones, such as heavy Fermion superconductivity in PrOs4Sb12, metal-insulator transition in PrRu4P12 and field-induced heavy Fermion state above antiferro-quadrupolar ordered state in PrFe4P12, have been most intensively investigated. Quite a few attractive features have been found also in Ce- and Sm-based skutterudites; such as recently found novel heavy Fermion state robust against magnetic fields in SmOs4Sb12. We discuss the novelty and variety of such attractive features in correlation with the unique crystal structure of the filled skutterudite.

The magnetic torque measurements were performed on two MgB2 single crystals with the different values of upper critical fields Hc2 (3.7 T and 3.1 T at 4.2 K). At low temperatures, the irreversible torque-vs-field curves τ(H) in the both samples show the peak effect, accompanied by the field-history dependence, close to Hc2 for all the field directions measured. With increasing temperature, the peak in τ(H) becomes less pronounced, and disappears around T = 27 K. In the sample with smaller Hc2, τ(H) curves display diamagnetic steps at the higher temperatures. On the other hand, in the sample with larger Hc2, such a step is not observed. Our results suggest that the order–disorder transition around the peak transforms to the first-order melting transition, which is very sensitive to the degree of disorder.

We have grown high quality single crystals of MgB 2 by the encapsulation method. A new method which combines the magnetic torque method and the field modulation method is successfully employed to detect the dHvA oscillation and the AC response of the superconductor down to the fields below H c2 . The AC torque signal indicates that the surface superconductivity develops well above H c2 and it evolves into the bulk superconductivity with decreasing field. The irreversible torque curve is observed at much higher fields than H c2 and can be attributed to a pinning effect of the surface vortices. The superconducting transition detected by the AC torque method significantly broadens indicating that the supercondcuting fluctuation is not negligible. It is suggested that both the surface superconductivity and the fluctuation contribute considerably to the broadening of the resistive transition. We have found that the damping of the dHvA signal from the π band is very large around H c2 due to the superconducting fluctuation and the pinning effect, but the damping rate becomes moderate with further decreasing field, implying that the superconducting gap may be small for the π band near H c2 .

We investigate a new route to quasi-one-dimensional spin-chain systems which originates from the charge-ordering transition out of a homogeneous mixed-valence state. We present evidence that Yb4As3 and P, Sb doped mixed crystals are well described by this mechanism. Many thermodynamic and low-temperature transport heavy-fermion-like properties can be explained by the existence of low-lying quasi-one-dimensional spin excitations in the Yb3+-chains. The observation of soliton excitations in a transverse external field gives further support to the existence of spin chains in Yb4As3. We also present recent results on spin-glass behavior at very low temperature caused by the interchain coupling and disorder. In addition, the yet unexplained magnetotransport effects are discussed.

CeRhSi 3 has the large electronic specific-heat coefficient γ = 120 mJ/mol K 2 and the high Kondo temperature T K ∼ 100 K, although its magnetic susceptibility follows the Curie-Weiss law and the specific heat indicates magnetic ordering at 1.8 K. In order to elucidate the 4f-electron nature in CeRhSi 3 , we have grown single crystals of CeRhSi 3 and of its reference material LaRhSi 3 and measured the electrical resistivity, the magnetic susceptibility and the de Haas-van Alphen (dHvA) effect. Comparison of the angular dependence of the dHvA frequency in CeRhSi 3 to that in LaRhSi 3 , indicates that the 4f-electrons of CeRhSi 3 are itinerant.

We have performed de Haas–van Alphen effect measurements on V3Si in both normal and mixed states. The oscillations with many frequency components observed in the normal state considerably differ from previously reported ones. We discuss this discrepancy in terms of domain structures formed at the martensitic transition of V3Si. The field dependence of the oscillation amplitude is determined.

We have performed the de Haas–van Alphen (dHvA) and the magnetoresistance experiments in UPt3. The result of the magnetoresistance is consistent with the topology of the Fermi surface predicted from the 5f-itinerant band theory. The main Fermi surfaces detected by the dHvA are also well explained by the 5f-itinerant band model, although the cyclotron effective masses with 15–105m0 are 10–20 times larger than the corresponding band masses.

We have observed a quantum Hall effect in the bulk quasi-two-dimensional conductor η-Mo 4 -O 11 . The Hall resistance exhibits well defined plateaux, coincident with pronounced minima in the diagonal resistance. We present data for several different samples and contact geometries, and discuss a possible mechanism for the quantum Hall effect in this system. We also discuss the implications of these findings in the light of recent predictions concerning chiral metallic surface states in bulk quantum Hall systems.

Cubic Sm3Te4 can be characterized as a semiconducting, inhomogeneous mixed-valence system. No evidence of charge ordering is found at low temperature, indicating that Sm2+ and Sm3+ ions are randomly distributed on one crystallographic position. The magnetization density of a Sm3Te4 single crystal was measured at 1.5 K using polarized neutrons, with a magnetic field applied along [1 1 0] . As the Sm3Te4 structure is not centric, the measured flipping ratios have been directly processed by the maximum entropy method and by a least-squares refinement. The two approaches are in agreement: under the action of the magnetic field, the Sm site splits into two subsites, with very different induced magnetization densities. Two possible explanations are proposed.

We have investigated the thermoelectric power ( S ), Hall coefficient ( R H ), and magnetoresistance (MR) of Pr x Fe 4 Sb 12 ( x ∼ 1 ) synthesized under high pressure. The dependence of S and R H on the Pr-site filling fraction x become apparent at low temperatures. In MR, we confirmed that the electrical resistivity is enhanced by the 4f-electron crystalline electric field effect below ∼ 10 K and suppressed by the 3d-electron spin fluctuation effect above ∼ 10 K . The change of magnetic state in Pr x Fe 4 Sb 12 with x , realized as a combined effect of 4f-electrons and the high electronic density of state at Fermi level, is well reflected in the transport properties.

We have succeeded in synthesizing new filled skutterudite SmFe 4 As 12 under high pressure. We found that SmFe 4 As 12 can be synthesized only in a narrow temperature range near 1170 K. The electrical resistivity shows metallic temperature dependence with the residual resistivity ratio is 20, indicating the reasonably high crystallinity of the sample. The magnetization and the specific heat measurements revealed that SmFe 4 As 12 undergoes a ferromagnetic transition at T C = 39 K .

We have synthesized the filled skutterudite Sm x Fe 4 Sb 12 under high pressure to improve the Sm-site filling fraction x. From the magnetic susceptibility, electrical resistivity and specific heat measurements, we confirmed a ferromagnetic transition at T C ∼ 43 K . We found no drastic change in the magnetic properties caused by the reduced number of the Sm-site vacancy, in contrast with the significant change of the magnetic ground state in Pr x Fe 4 Sb 12 ; from ferromagnetic to non-magnetic one. Such a different response of the magnetic properties to the change in rare earth site vacancy is discussed.

The ac-susceptibility data in a crystal of LuNi 2 B 2 C reveal only a peak effect anomaly for the fields applied in the basal plane. However, multiple anomalous variations in critical current density are observed during rotation of the field from [1 1 0]/[1 0 0] to [0 0 1]. Coupling in the symmetry of the vortex lattice with that of the crystalline lattice can result in an effective pinning being different in different directions. This in turn yields a large variation in the values of the onset field of spatial order–disorder transition, for different orientations of the field.

We have studied the electronic structures of CeRu 2 ( Si 1 - x Ge x ) 2 single crystals, whose ground state changes from paramagnetic state to antiferromagnetic state with increasing Ge concentration across the quantum critical point, via the dHvA effect. It has been reported that the effective masses of the up and down spin conduction electrons in CeRu 2 Si 2 are considerably different, although their Fermi surfaces are nearly the same. Such anomalous conduction electron state is found to exist above the metamagnetic transition fields in both the samples of the paramagnetic and antiferromagnetic ground state.

We have succeeded in growing single crystals of the filled skutterudite compound SmRu 4 P 12 . To clarify the magnetic anisotropy, we have measured the specific heat C and the magnetization M as functions of temperature T , magnetic field H , and magnetic fields directions. In the H dependence of M at T = 15.5 K , between the two characteristic temperatures T MI = 17.5 and T * = 14 K , we have observed clear magnetic anisotropy under high magnetic fields. The anisotropy decreases with decreasing H , and becomes within the experimental uncertainty below 1 T. T MI determined by the specific heat under magnetic fields is basically field independent up to 8 T, while T * exhibits evident anisotropy. These results could be a clue to understand the ordered state in this material.

We have succeeded in synthesizing the filled skutterudite compound Pr x Co 4 Sb 12 under high pressures. Pr site filling factor was estimated to be about 50 ± 10% by powder X-ray diffraction and chemical composition analysis using field emission electron microscope. Apparent expansion of lattice constant 9.09 A compared to that of CoSb 3 9.03 A is also indirect evidence of successful filling of Pr-ions. In the magnetization and specific heat measurements, no anomaly suggesting phase transition has been found down to 2 K.

Neutron diffraction experiments were performed to investigate a nature of the antiferromagnetic ordered phase below T N = 1.6 K of the pressure-induced superconductor CeRhSi 3 . We observed incommensurate magnetic reflections characterized by the wave vector Q = ( ± δ , 0 , 0.5 ) ( δ ∼ 0.215 ) . The antiferromagnetic ordered state can be interpreted as a spin-density wave formation by taking account of the results on de Haas–van Alphen (dHvA) signals in CeRhSi 3 where the 4f-electrons of CeRhSi 3 are itinerant.

We have studied the de Haas–van Alphen effect in the commensurate (C) and incommensurate (IC) phases of PrB 6 . It is found that the amplitudes and effective masses of the two oscillations α 1 and α 2 from the main Fermi surface are approximately the same in the C phase while they are considerably different in the IC phase.

We have performed the dHvA measurements on Ce x La 1 - x B 6 and Pr x La 1 - x B 6 compounds to study spin splitting of the Fermi surfaces. In PrB 6 we have found new frequency branches to confirm that the Fermi surface splits into up and down spin Fermi surfaces, whereas no spin splitting has been found for x = 0.25 , 0.5 , 0.75 . We have also found several new frequency branches in CeB 6 . The new frequency branches imply that the Fermi surfaces of up and down spin conduction electrons are significantly different in CeB 6 as well as in PrB 6 .

We have successfully grown single crystals of CeAu 2 Si 2 with the Neel temperature of 8.1 K. The magnetic properties are very anisotropic in the antiferromagnetic state as well as in the paramagnetic state. When a field is applied parallel to the c -axis, the single crystal exhibits a sharp metamagnetic transition of first order at 4.2 T, while the magnetization increases almost linearly with fields parallel to the a -axis.

In Yb pnictides with anti-Th 3 p 4 structure, the valence of Yb decreases from about 2.25 in Yb 4 As 3 to about 2 in Yb 4 Bi 3 with increasing weight of pnictogen. In Yb 4 As 3 , charge ordering around 300 K is observed and in the charge ordered phase heavy fermion behavior is seen in spite of extremely low carrier concentration. On the other hand, Yb 4 Sb 3 is a valence fluctuating system. So, to make systematic studies from Yb 4 As 3 to Yb 4 Sb 3 we grew single crystals of Yb 4 (As 1− x Sb x ) 3 . With increasing Sb content, the absolute value of the resistivity decreases due to the increase of the number of carriers and the charge ordering temperature decreases reflecting the increase of the screening effect, and at 29% charge ordering seems to disappear. The γ-value, however, is still large even in Sb 29% sample. The large γ-value of Yb 4 (As 1− x Sb x ) 3 is considered to be independent ofthe carrier concentration.

Charge ordering of Yb ions in the quantum spin chain system Yb4As3 has been investigated by 171Yb NMR. Clear evidence for the existence of 4f holes on Yb2+ sites has been obtained from the non-monotonic T-dependence of the resonance shift K(T).

We have found an anomaly in magnetic field dependence of the de Haas-van Alphen (dHvA) frequency of ZrZn 2 . Pressure dependence of this anomaly suggests an existence of two distinct ferromagnetic states and then a “nested” phase diagram similar to that of UGe 2 . The Stoner exchange parameter and the exchange splitting energy are 400 and 66 meV, respectively, which are derived from comparing the field dependence of the dHvA frequency difference with the magnetization. The two parameters do not change in both the low and slightly higher average moment states, suggesting that the phase transition between these states is ascribed to the change in the difference of majority and minority spin carrier densities.

We have measured the field-angle-dependent specific heat, C ( H , θ ) , in the unconventional heavy-fermion superconductor CeCoIn 5 down to ∼ 0.29 K . In a magnetic field rotating in the tetragonal c-plane, a clear fourfold angular oscillation is observed in C ( H , θ ) with the minima (maxima) occurring along the [1 0 0] ([1 1 0]) directions. Oscillation persists down to low fields H ⪡ H c 2 , thus directly proving the existence of gap nodes. Position of the minima in C ( H , θ ) indicates that the gap node is located along the [1 0 0] and [0 1 0] directions, implying that the superconducting gap symmetry of CeCoIn 5 is most probably of d xy type.

The a-axis resistivity in UGe2 is measured in the temperature range between 0.3 and 4.5 K and in magnetic fields up to 17.5 T applied parallel to the a axis, which is the easy axis of magnetization. The T2 coefficient A of the resistivity is 0.008 μ Ω cm/K2 at zero field and is reduced by ∼50% with increasing field to 17.5 T.

Inelastic neutron scattering experiments under magnetic field were performed on the one-dimensional quantum antiferromagnet Yb4As3. When a magnetic field is applied perpendicular to the Yb 3 + chain, the material exhibits a gap-opening phenomenon due to the induced staggered field originated from the Dzyaloshinsky–Moriya interaction. It was confirmed that the spectrum remains gapless when a magnetic field is applied parallel to the Yb 3 + chain. Clear evidence for the incommensurate mode which is predicted by the theories was found.

We have done the de Haas-van Alphen (dHvA) experiments to clarify the Fermi surface properties such as Fermi surface, cyclotron mass and scattering lifetime of the conduction electrons for the highly correlated electron systems as in PrCu 2 with the singlet ground state, a typical heavy Fermion compound CeRu 2 Si 2 , a generalized FFLO superconductor CeRu 2 and an unconventional superconductor UPt 3 .

A 40 T class hybrid magnet system, built at the National Research Institute for Metals, Japan, has been used to measure the transport properties of organic conductors, η -MoO 11 , etc. A Fourier-transform spectrometer in the milli- to submillimeter range has been developed using a lamellar grating, and has been used in magneto-optical studies of the spin-Peierls oxide CuGeO 3 . Fermi surfaces have been investigated extensively using a 16 T magnet with a dilution refrigerator, and de Haas-van Alphen oscillations were clearly observed in the mixed state, as well as in the normal state for YNi 2 B 2 C Crystals. Magnetization measurements have been performed on the hexagonal intermetallic compound RPd 2 Al 3 using pulsed magnetic fields. The present status of the high-field magnets and the experimental results obtained at the NRIM are described.

The thermal conductivity κ of Yb 4 (As 1− x P x ) 3 ( x =0 and 0.3) was measured in the temperature range between 0.1 and 7 K in applied magnetic fields up to 8 T. The fact that κ ( T ) follows, between 0.4 and 3 K, the relation aT + bT 2 confirms our earlier interpretation of the dominating role of magnons both as heat carriers and as scatterers for the phonons. Above 1 K, κ decreases with increasing magnetic field, the opening of a gap in the magnon-excitation spectrum being a possible explanation of this behavior.

The Shubnikov-de Haas (SdH) measurements of the two dimensional organic conductor (BEDT- TTF)2TlHg(SCN)4 have been performed to investigate the Fermi surface reconstructed by the spin density wave formation. At 0.05 K, ten different SdH oscillations are found. A model of the reconstructed Fermi surface is proposed on the basis of the relation between the observed SdH frequencies.

X-ray absorption (XAS) and its magnetic circular dichroism (XMCD) were measured at the Ce ${M}_{4,5}$ absorption edges of ferromagnetic CeRu${}_{2}$Ge${}_{2}$ and paramagnetic CeRu${}_{2}$Si${}_{2}$: both compounds are considered to be located near the boundary of delocalization of Ce 4$f$ electrons. While the XAS line shape varies clearly reflecting the variation in the 4$f$ delocalization, the line-shape variation in XMCD is hardly discernible under various conditions of temperature and magnetic field. The XAS line-shape variation can be explained as effects of the variations in the $4f$ occupation number and in the ratio of $J=7/2$ states in the ground states, both of which are closely related to the 4$f$ delocalization. The 4$f$ delocalization also causes a decrease in the ratio of the orbital magnetic moment to the spin magnetic moment. The magnetic-field dependence of XAS suggests that the Ce 4$f$ electrons retain a delocalized character across the metamagnetic transition in CeRu${}_{2}$Si${}_{2}$.

Shubnikov—de Haas (SdH) measurements in the quasi-two-dimensional (2D) organic conductor (BEDT-TTF) 2 TlHg(SCN) 4 have been carried out to investigate the ground state. The closed orbit of the 2D Fermi surface and the magnetic breakdown orbit are observed above 10 T. Below 3 T, three small closed orbits are found, which are made by the nearly perfect nesting of the one-dimensional (1D) Fermi surface. The results indicate that the ground state is a spin density wave state at low magnetic fields and that the nesting is removed by high magnetic fields.

We have studied the de Haas-van Alphen (dHvA) effect for field ranges both below and above the metamagnetic transition field (Hm) in CeRu2Si2. The Fermi surfaces are found to change from those of the itinerant 4f electrons below Hm to those of the localized 4f electrons above Hm. The dHvA frequency around Hm has been measured in detail as function of magnetic field strength and temperature. The observed variation of the frequency implies that the transition of the Fermi surface becomes less sharp at higher temperatures.

Crystal field (CF) excitations in the ternary intermetallic uranium compound U 3 Pd 20 Si 6 have been measured using inelastic neutron scattering. Three inelastic peaks were observed at energy transfers ∼12, ∼23 and ∼32 meV. This is direct evidence that the 5f electrons in this material are well localized. From this result and the bulk properties of U 3 Pd 20 Si 6 , possible CF level schemes are discussed. The strong magnetic excitation below the antiferromagnetic phase transition temperature of 19 K is also reported.

We have investigated the difference in the low-T specific heat, C(T, B), of single- and multi-domain Yb 4 As 3 crystals in magnetic fields B≤4 T. Upon increasing field, which was applied parallel to the trigonal axis, the C(T)/T values of the single-domain sample have been found to be less reduced than that of the multi-domain one. Furthermore, a minimum value of C(T)/T which is unaffected at B≥ 1 T is observed for the single-domain sample around 0.25 K. This behavior cannot be explained by the S = 1/2 Heisenberg antiferromagnet with the intrachain coupling determined by the inelastic neutron scattering. The interchain coupling appears to be responsible for the reported C(T)/T behavior below 1 K.

To investigate the anomalous transport property and the electronic structure near the Fermi level of Yb 4 As 3 , we have measured the temperature dependence of reflectivity spectra of Yb 4 (As 1− x P x ) 3 ( x =0, 0.05, 0.15) in the far-infrared region. In Yb 4 As 3 , a Drude-curve with very low carrier density and long relaxation time appears at temperatures below 70 K. Coincidently, a peak appears around 15 meV. The peak is considered to originate from the hybridization between Yb 3+ 4f-hole and 5d states on the Yb 3+ chain.

We report the result of an inelastic neutron elastic scattering experiment on U3Pd20Si6. We found a crystalline electric field excitation around 23 meV, indicating localized character of the 5f electrons in U3Pd20Si6. We also observed a sharp peak at dE=2.8 meV in the magnetic excitation spectra at 7 K, below the antiferromagnetic transition temperature 19 K, which may be attributed to antiferromagnetic spin wave excitations.

We report the magnetic phase diagram of Ce3Pd20Ge6 under uniaxial pressure. It is found that the phase diagram changes considerably with pressure, but that the antiferromagnetic and ferroquadrupolar ordering temperatures do not change within experimental accuracy.

We have studied the magneto-oscillatory behavior of quasi-two-dimensional (quasi-2D) organic conductors of the type (BEDT-TTF)2XHg(SCN)4, where X = K, Rb, NH4, in order to probe the underlying magnetic behavior of these materials. The K and Rb compounds are metallic down to 50 mK, but are not superconducting. They both display a dual series of magneto-oscillations, a magnetic ordering at low temperatures, below about 10 K, and a sharp drop in the magnetoresistance associated with the destruction of this phase with the application of high magnetic fields at low temperatures. In contrast, the NH4 material is a superconductor at low temperatures (below 1K) up to a pressure of at least 4 kbar. It also displays a complex background magnetoresistance upon which is superposed a single oscillation series. In all three organic materials, there is a strong interaction between the underlying magnetic phases (which influences the open orbits) and the magneto-oscillations which result from the quasi-2D Fermi surface behavior.

We report systematic high-magnetic-field and low-temperature measurements on several members of the α-(BEDT- TTF)2MHg(SCN)4 family of low-dimensional organic conductors. For M = K, transport, high-pressure and magnetic studies show the presence of a magnetic phase which is removed either with high magnetic fields or with high pressure. For M = Rb, transport measurements indicate the existence of a magnetic phase similar to the case for M = K, but with a higher transition temperature and critical field. For both M = K and Rb the split Landau level phenomenon is observed. We also report the pressure dependence of the Fermi surface for M = NH4 and K.

We report the first successful dHvA experiment under uniaxial compression in such compound Ce 3 Pd 20 Ge 6 that exhibits quadrupolar ordering and in its reference compound La 3 Pd 20 Ge 6 . The frequency changes with uniaxial pressure are qualitatively similar in the two compounds, but the magnitude of the frequency change in Ce 3 Pd 20 Ge 6 is about twice as much as that in La 3 Pd 20 Ge 6 , implying that the degenerate ground state of the localized f electrons is significantly affected by the uniaxial compression.

One-dimensional (1D) magnetic properties in the charge-ordered phase of Yb 4 As 3 has been studied by polarized-neutron diffraction. Field-induced magnetic moment on the 1D Yb 3+ -ion chain under the field of 7 T parallel to the chain behaves as that of the spin-1/2 1D Heisenberg antiferromagnet with g ∥ =3.0. In the case of the field perpendicular to the chain, we observed not only the same behavior of induced moments with g ⊥ ≃1.2 but also a remarkable enhancement below about 10 K. The experimentally observed 1D magnetization can be reproduced well by the theory based on Dzyaloshinskii–Moriya interaction inducing effective staggered field by uniformly applied field.

We report on low- T ( T ⩾0.02 K) measurements of the electrical resistivity, ρ ( T , B ), and the magnetic AC-susceptibility, χ ac ( T , B ), on the low-carrier density, one-dimensional S= 1 2 antiferromagnet Yb 4 As 3 in magnetic fields B ⩽19 T . For 2 K⩽ T ⩽20 K we find ρ − ρ 0 =AT 2 ( ρ 0 : residual resistivity), with a large coefficient A ≈0.75 μΩ cm/K 2 followed by a minimum around 1 K and a 0.1% increase for T →0. In finite fields and below about 5 K, ρ ( T , B ) shows a history-dependent hysteretic behavior. The oscillatory behavior superimposed is attributed to the Shubnikov–de Haas effect arising from a low density of mobile As–p holes. For T ⩾0.4 K , χ ac ( T ) follows the prediction of the quantum sine-Gordon model. A cusp-like anomaly is found at 0.15 K.

The dHvA effect experiments on Nb have been performed in low fields down to H c2 using a standard field modulation method. The signal amplitude becomes much smaller below H c3 than that expected from a straight extension of the Dingle plot from the higher fields and is below the noise level around and below H c2 . The rapid decrease of the amplitude below H c3 is simply understood as arising from the screening of the modulation field and is expected to be observed for other homogeneous type-II superconductors. The present observation is inconsistent with those reported for materials such as NbSe 2 , where the same or comparable amplitudes to those in the normal state are detected below H c2 by the field modulation method.

We measured the magnetic susceptibility and the specific heat of a single-domain sample of Yb4As3 under the magnetic field along the trigonal axis. The magnetic susceptibility in the charge ordered phase is very anisotropic and the upturn at low temperatures becomes smaller than that of the multi-domain sample. The suppression in the specific heat by applied fields parallel to the trigonal axis becomes weak compared with that of the multi-domain sample. These results indicate that this anisotropy is explained by the alternating Dzyaloshinsky–Moriya interaction and the effect of the alternating off-diagonal g-tensors expected from the symmetry of Yb3+ sites on the one-dimensional chains.