Tomohiko Kuwai

Magnetic properties of the diamond chain compound Cu3(CO3)2(OH)2

Azurite (Cu 3 (CO 3 ) 2 (OH) 2 ) is a model substance of a diamond spin chain, one of frustrated antiferromagnetic quantum spin chains. The high field magnetization up to 60 T, magnetic susceptibility, magnetic entropy, muon spin relaxation and 1 H-NMR of azurite have been measured using single crystals. A distinct 1/3 magnetization plateau is confirmed to be present in the magnetization curve. Two resonance peaks of 1 H-NMR. were observed. By analyzing temperature dependencies of their hyperfine shift. we found two different local susceptibilities which correspond to susceptibility of dimer and monomer spins, respectively. New field induced phase transition was found to occur at a critical field where the magnetic plateau onsets. A short range magnetic ordering developed in a peculiar two-stage process, which was revealed by temperature dependence of the magnetic specific heat and susceptibility.

Origin of Weak Ferromagnetism in YbxFe4Sb12, Relationship between Weak Ferromagnetism and Filling Ratio x

The magnetization and specific heat of single-crystalline samples of filled-skutterudite compounds Yb x Fe 4 Sb 12 were measured. Six single crystals with the filling ratio of Yb, x , from 0.875 to 0.910 were prepared. The weak ferromagnetism of Yb x Fe 4 Sb 12 appearing at low temperatures was found to strongly correlate with x ; with increasing x from 0.875 to 0.910, the transition temperature, T C , decreases from 17 to 5 K and the weak-ferromagnetic moment, m 0 , decreases from 0.066 to 0.005 µ B /Fe. From these trends, both T C and m 0 were expected to reach zero at the critical concentration, x c =0.93. In the temperature dependence of the specific heat, no anomaly at T C was observed, reflecting that m 0 is extremely small compared with the effective Bohr magneton number. With the application of pressure, the T C of the sample with x =0.882 increases rapidly, with the ratio of d T C /d P =+5.27 K/GPa. This weak ferromagnetism of Yb x Fe 4 Sb 12 originates from the itinerant 3d electrons of Fe in an...

Dense Kondo Effect in Caged Compound CeRu2Zn20

We prepared single crystals of the caged compound CeRu2Zn20 by the flux method, and measured the magnetization, magnetic susceptibility, specific heat, and electrical resistivity. The lattice constant measured at room temperature suggests that the Ce ion is trivalent in this compound. The temperature dependence of magnetic susceptibility obeys the Curie–Weiss law with the effective Bohr magneton of Ce3+ at high temperatures. However, at low temperatures, CeRu2Zn20 indicates no phase transition down to 2 K and shows typical behaviors of a heavy Fermion system; the enhanced magnetic susceptibility χ0, the enhanced electronic specific-heat coefficient γ0, and the electrical resistivity with the temperature dependence of \(AT^{2}\), although these parameters somewhat depend on samples. The Wilson ratio \(R_{\text{W}}\) of χ0/γ0 is approximately 2, which does not depend on samples. A/γ0 is plotted on the line of \(N = 2\) in the new Kadowaki–Woods plots. The Kondo temperature \(T_{\text{K}}\) is roughly estima...

Magnetic, Electric and Thermal Properties of NdNiAl4 Single Crystal.

The electrical resistivity, magnetization, specific heat and thermoelectric power measurements were performed on a NdNiAl 4 single crystal along the principal axes of the orthorhombic cell. The easy axis of magnetization was parallel to the b axis below 20 K. The spin-flipping was observed at the magnetic field 4.4 T along the b axis at 2 K. The magnetic phase diagram was determined from the spin-flipping field. The huge magnetic anisotropy energy was estimated from the experiments of the magnetic susceptibility and magnetization. The energy gap newly occurred below T N was observed in the electrical resistivity along the b axis. From this result we have speculated that a new magnetic periodicity is made along the b axis below T N . The magnetic susceptibility for the principal axes was discussed on the bases of the crystalline-electric-field and molecular-field theories.

RKKY Interaction and Kondo Effect in (Ce, La)PdSn

Measurements of the magnetic susceptibility (2–300 K), electrical resistivity (70 mK–300 K), specific heat (70 mK–150 K) and thermoelectric power (0.3–300 K) have been carried out on Ce x La 1- x PdSn. For all these quantities, the crystalline electric field (CEF) effect on Ce 3+ state was observed: the CEF splitting scheme does not change much for x ≥0.3. The Neel temperature decreases monotonically with decreasing Ce concentration, and the long-range antiferromagnetic order disappears for x around 0.1. The thermoelectric power of Ce x La 1- x PdSn shows complicated structures at low temperatures. These results were discussed from the viewpoint of coexistence and competition between the RKKY interaction and the Kondo effect.

Magnetic Phase Diagram of Ce(Ni1-xPdx)2Ge2.

We have measured the temperature dependence of the magnetic susceptibility, the electrical resistivity, the specific heat and the Hall coefficient on the pseudo-binary series Ce(Ni 1- x Pd x ) 2 Ge 2 (1.0≥ x ≥0.0). The Neel temperature decreases monotonously from 5.1 K for CePd 2 Ge 2 to 2.8 K for Ce(Ni 0.8 Pd 0.2 ) 2 Ge 2 with decreasing Pd concentration. For x ≤0.1, the ground state is paramagnetic.

Enhancement of the curie temperature due to the coupling between Fe itinerant electrons and Dy localized electrons in DyFe2Zn20

The temperature dependences of the magnetization and the specific heat of the ferromagnetic compound DyFe2Zn20 have been measured in detail in various magnetic fields. We have observed anomalous magnetic behaviors, i.e., a strong anisotropy at 2 K, the disappearance of this anisotropy at temperatures between approximately 30 K and Tc, and an anomalous behavior of the specific heat in magnetic fields at temperatures near 20 K. These anomalous phenomena have been analyzed based on the strong exchange interaction between the Fe itinerant electrons and the Dy localized electrons, as well as the crystalline electric field, the Zeeman energy, and an usual exchange interaction between two Dy atoms. The higher Tc of DyFe2Zn20 compared with that of DyRu2Zn20 is caused by this exchange interaction between the Fe and the Dy atoms.

Disappearance of magnetic moments in CePd1−xNixAl

Abstract We present the chemical pressure effect on the specific heat and magnetic susceptibility in the substituted system CePd1−xNixAl. By substitution of 10% of Ni, TN has almost disappeared. Further substitution of Ni drastically diminishes the magnetic moment and the effective number of Bohr magnetons. The entropy integrated up to 10 K is 66% for CePdAl, and it decreases to 3% of R ln 2 with increasing x. The electronic specific-heat coefficient C/T approaches 1.1 J/mol K 2 for CePd0.9Ni0.1Al at low temperatures. Single crystals for x=0.0 and 0.1 have been grown to investigate the magnetic anisotropy.

de Haas-van Alphen effect and Fermi surfaces of magnetic dense-kondo compound CeNi2Al5

The experiments of de Haas-van Alphen (dHvA) effect have been carried out at temperatures down to 40 mK in a magnetic dense-Kondo compound CeNi 2 Al 5 with an incommensurate magnetic structure. A complex phase diagram of the magnetic transition field versus temperature is completed. Many branches of the dHvA frequencies observed in the higher-field regions, II, III and IV, have been understood better by the branches predicted from the theoretical Fermi surfaces of nonmagnetic reference-sample LaNi 2 Al 5 rather than the theoretical ones in CeNi 2 Al 5 with 4 f electrons treated as itinerant. Branches observed in the lowest field region I are not clearly analyzed with the theoretical prediction in LaNi 2 Al 5 or CeNi 2 Al 5 . The electrons with heavy cyclotron mass are observed in the region IV; 12.4 m 0 in η branch, 11.2 m 0 in ζ branch and 9.6 m 0 in θ branch. Some pairs of parallel branches are observed due to the spin-splitting related to the magnetism, and the exchange energy Δ E is obtained; Δ E =12....

Tuning of Magnetic Properties and Kondo Effect by Cu Concentration in Ce(Pd1-xCux)2Al3

The electrical resistivity, magnetic susceptibility and specific heat measurements were performed on Ce(Pd 1- x Cu x ) 2 Al 3 ( x =0.0–0.7) system to investigate the effects induced by Cu substitution in the heavy fermion compound CePd 2 Al 3 . A dramatic evolution of the magnetic properties was observed with the substitution of Pd by Cu: (1) a small amount of Cu ( x < 0.1) in CePd 2 Al 3 leads to a rapid decrease of the antiferromagnetic transition temperature T N ; (2) passing through a crossover region without a long-range magnetic order, a ferromagnetic-like state, which reveals an enhanced magnetic susceptibility and a distinct peak in the specific heat curve at low temperatures, occurs around x =0.1–0.4; (3) by furthering the substitution through a second crossover region, however, the antiferromagnetic ordering is recovered close to x =0.5–0.7. A decrease tendency of the Kondo temperature T K with increasing x is derived from the analysis on the specific heat results. It is suggested that the chang...