Kiyoo Sato

Magnetic Properties of Cobalt and Nickel Dichalcogenide Compounds with Pyrite Structure

The magnetic properties of dichalcogenide compounds, CoS 2 , CoSe 2 , NiS 2 , NiSe 2 and the system Co(S x Se 1- x ) 2 , were studied by means of magnetic measurement, neutron diffraction and NMR. The exchange interaction J s w of the ferromagnetic CoS 2 ( T c =124°K, θ p =220°K, p eff =1.76µ B , n =0.84µ B and H i =52 kOe) was estimated to be 24 cm -1 per Copair from the analysis of spin wave theory. While, CoSe 2 ( T N =90°K, θ p =-160°K and p eff =1.72µ B ) showed an antiferromagnetic spin ordering with MnSe 2 type. NiS 2 (θ p =-740°K and p eff =2.48µ B ) had no magnetic ordering even at 4.2°K. NiSe 2 exhibited weak constant paramagnetism with metallic conductivity. In Co(S x Se 1- x ) 2 , (0≤ x ≤1), the magnetic properties and the magnetic phase diagram were determined, and this system showed to have “low spin state” with 1µ B per Co. Some discussions were given from the theoretical stand points.

A New Dense-Kondo Compound CeNiAl4

Experiments of electrical resistivity, specific heat and magnetic susceptibility of a ternary intermetallic compound CeNiAl 4 have been carried out. It is found that CeNiAl 4 is a new member of the dense-Kondo compounds in the valence-fluctuation regime and that CeNiAl 4 is nonmagnetic above 1.6 K. The susceptibility χ 0 and the electronic specific heat coefficient γ 0 which are extrapolated to 0 K are 5.6×10 -3 emu/mol and 204 mJ/mol·K 2 , respectively. The Kondo temperature T K is estimated to be 67 K or 86 K.

New Type Metamagnetism in Co(SxSe1-x)2: Exchange-Compensated Paramagnetism

The magnetic phase diagram of Co(S x Se 1- x ) 2 , the solid solution between ferromagnetic CoS 2 and antiferromagnetic CoSe 2 , has been given by neutron diffraction experiment, where the paramagnetism at absolute zero was found in the range 0.5< x <0.88. This paramagnetic state is named “exchange-compensated paramagnetism”. A new type metamagnetism has been found in this paramagnetic state at x =0.86. This behavior had been already predicted theoretically by M. Hattori, K. Adachi and H. Nakano in J. Phys. Soc. Japan 26 (1969) 642. The metamagnetic properties have been measured under a strong magnetic field up to 75 kOe and in the temperature range 4.2°K to 800°K. The metamagnetism shows the hysteresis without remanence below 34°K and the saturation moment agrees with that of CoS 2 . The obtained results have been analyzed from the thermostatistical standpoint with an analogy of the condensation of imperfect gas and the critical indices have been determined. The origin of the exchange-compensated paramag...

Electrical Resistivity, Magnetic Susceptibility and Specific Heatof a New Dense Kondo Compound CeNi2Al5

The electrical resistivity, magnetic susceptibility and specific heat of a ternary intermetallic compound CeNi 2 Al 5 have been measured. It is found that CeNi 2 Al 5 is a new dense Kondo compound with the Neel temperature of 2.6 K. The temperature dependence of the resistivity has a broad peak at 4.0 K, reflecting the coherence of the Kondo scattering. The ground state of the Ce ions is determined to be a doublet from the result that the entropy equals R ln 2 when we include the area of a tail extended by the short-range order. A spin-flip is observed in high magnetic field, and a magnetic phase diagram is roughly estimated.

Magnetic Properties of the Dense Kondo Compound YbNiSn

Specific heat measurements revealed that YbNiSn is a dense Kondo compound with a large electronic specific heat coefficient γ of 300 mJ/mol K 2 . This compound orders magnetically at 5.5 K, below which the ferromagnetic moment appears along the c -axis. The magnetization along the a -axis vs external magnetic field H curve shows three anomalies at H C1 , H C2 and H C3 , whereas the magnetization along the b -axis increases gradually from zero without anomalies. These results suggest that YbNiSn is the weak ferromagnet with the ferromagnetic moment along the c -axis, which is caused by the canting of antiferromagnetic sublattice within the ac -plane. The magnetic field dependences of the electrical resistivity of YbNiSn are strongly correlated with the magnetizations.

On the Magnetocrystalline Anisotropy of Iron Selenide Fe7Se8

Magnetization measurements along the a -and c -axes of a single crystal of a compound Fe 7 Se 8 have been carried out in magnetic fields up to 92 kOe over the temperature range 4.2° to 300°K, together with magnetic torque measurements on the b c -plane up to 9 kOe. The results of magnetization measurements along the c -axis lead to the magnetocrystalline anisotropy energy of the form, E (θ)=- K 0 |cos θ|+ K 3 cos 2 θ+ K 4 cos 4 θ, the last term being for minor correction. In this expression θ is an angle between magnetization and field direction. The measured values of anisotropy constants K 0 and K 3 at 290°, 77° and 4.2°K are K 0 =0.3×10 6 , 32×10 6 and 65×10 6 erg/cc and K 3 =2.5×10 6 , 18×10 6 and 35×10 6 erg/cc, respectively. From the magnetocrystalline energy mentioned above, it can be shown that the magnetic moment takes a conical distribution around the c -axis at low temperatures. The results of torque measurements on the b c -plane is reproduced by assuming a triad crystal domain structure.

Formation of Kondo lattice in La1−xCexNi

Temperature dependences of the resistivity and the susceptibility of single crystals of solid solution La 1- x Ce x Ni have been measured in the temperature range 2–300 K. We have obtained a phase diagram of La 1- x Ce x Ni which is consisted of three parts; (1) isolated Kondo region ( x 0.6 and high temperature region), where the 4f electron behaves as fairly localized electron although the valence of the Ce ion is more than three and (3) Kondo lattice region ( x >0.6 and low temperature region), where the 4f state becomes a delocalized state.

Detection of Ni magnetic moment in GdNi2 compound by magnetic Compton profile (MCP) method

The Ni magnetic moment in the GdNi2 Laves phase compound is studied in detail by the use of the magnetic Compton profile (MCP) method. Analysis of the MCP, measured at 30 K, reveals that the spin component of Ni 3d electrons coupled antiparallel to that of Gd 4f electrons, and it was confirmed that the Ni retains a spin magnetic moment of 0.16 ± 0.08 μB. Furthermore, the total magnetic moment, including the angular momentum component, is found to be 0.23 ± 0.11 μB and this value that is obtained is in accord with that derived from direct measurement of the bulk magnetization. Our finding of the existence of the Ni magnetic moment contradicts the well-known fact that Ni loses its magnetic moment in the Laves phase of rare-earth (RE)–Ni compounds. In addition, the magnetic moment originating from the electrons with s- and p-character, which are donated by the Gd and Ni atoms, is also observed and quantified.

High Field Magnetoresistance and de Haas-van Alphen Effect in CeNi

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in CeNi in the field up to 150 kOe and at temperature down to 0.4 K. This material is found to be a compensated metal with equal carrier concentration of electrons and holes. The open orbits exist along the b - and c -axes. Four dHvA branches have been found in the field along the b -axis. The dHvA frequencies and the cyclotron masses are 3.60 ×10 7 Oe (10.3 m 0 ), 1.25 ×10 7 Oe (8.91 m 0 ), 6.58 ×10 6 Oe (3.05 m 0 ) and 2.15 ×10 6 Oe (2.58 m 0 ).

Correlation between the specific heat and high field magnetism of La1−xCexNi at low temperatures

Abstract The specific heat of La 1− x Ce x Ni has been measured from 1.3 to 4.2 K and high field magnetization was measured in magnetic fields up to 100 kOe at 4.2 K. The correlation between the specific heat coefficient and the susceptibility at low temperatures was discussed on the basis of the Fermi liquid theory.