Y. Okayama

Why the magnetic and electrical properties of Ce monopnictides are so sensitive to pressure

Abstract The effects of pressure on the electrical and magnetic properties of CeX (X = P, As, Sb and Bi) have been investigated and are reviewed, illustrating how the high pressure technique can be used to gain information about the electronic and magnetic state of these compounds. Most recently, a comprehensive pressure-temperature phase diagram has been established for CeP. The overall features of the highly unusual behavior revealed in these compounds can be understood qualitatively on the basis of this phase diagram. However, some phenomena, such as a huge enhancement of the resistivity induced by applying pressure in CeSb, still remain unexplained.

Pressure induced electrical and magnetic properties in Ce-monopnictides; CeX(X = P, As, Sb and Bi)

Abstract The high pressure effects on the temperature dependent resistivity of single crystalline CeX (X = P, As, Sb, and Bi) have been studied up to 8.5 GPa. An anomalous behavior in the resistivity versus temperature curve, R ( T ), is observed in all these compounds. The anomalous temperature dependent resistivity seems to correlate with the electronic state affected by the crystal field effect and the magnetic phase transitions, which is characteristic to all these compounds.

Pressure dependence of the crystal field state of a low carrier system CeP

Abstract Pressure dependence of the crystal field splitting in CeP has been studied by inelastic neutron scattering up to 0.8 GPa. It was found that the Γ7−Γ8 crystal field splitting in CeP decreases by about 10% from that at ambient pressure by applying a pressure of 0.8 GPa at temperatures below 60 K. Evidence for the temperature dependence of the pressure effect is seen.

Neutron scattering investigations of magnetic ordering and crystal field excitations in CeAs under high pressure

Abstract Elastic neutron scattering experiments on CeAs have been performed under high pressure. A new magnetic ordering with a ferromagnetic component is induced above ∼1.1 GPa, and a magnetic P-T phase diagram up to 3 GPa is determined. A qualitative aspect for the relation between the pressure-induced new magnetic phase and the crystal field splitting is discussed.

Pressure‐induced electrical and magnetic properties in CeAs, CeSb and CeBi

Electrical resistance of single‐crystalline CeAs, CeSb, and CeBi has been measured under hydrostatic pressure. In CeAs and CeSb, pressure enhances the change of overall features in the resistance‐temperature R(T) curves. Resistance anomalies associated with magnetic phase transitions are observed and are found to be sensitive to pressure. It is noted that the R(T) curve of CeAs at ∼3 GPa is similar to that of CeSb at ambient pressure.

Anomalous pressure-temperature-dependent Hall constants in CeP and Yb4As3

Abstract The Hall coefficient of CeP is found to change in sign from negative to positive with increasing pressure. This result clearly indicates the fact that there exists a successive electronic transition from a dense Kondo to a normal metal through a mixed-valence state. For Yb4As3, the huge peak in the temperature-dependent Hall coefficient is found to decrease with increasing pressure. This result indicates that the anomalous temperature-dependent resistivity is primarily caused by the carrier concentration depending strongly on temperature.

Transport properties under high pressure of the dense Kondo compounds CePdSn and YbB12

Abstract We have measured the electrical resistance of the metallic dense Kondo compound CePdSn and the semiconducting dense Kondo compound YbB12 under hydrostatic pressure up to 80 kbar. The pressure dependence of the resistance and its implications for the pressure dependence of the gap energy is discussed.

High pressure specific heat investigation of the magnetic transition in CeP

Abstract The specific heats of CeP under hydrostatic pressures up to 0.5 GPa were measured over a temperature range of 1.6–25 K. The antiferromagnetic transition at 10.2 K was found to split into two transitions. One of them exhibited a large positive pressure dependence of 20 K/ GPa while the other showed a weak pressure dependence.

Magnetization at high pressure in CeP

Abstract We have investigated the pressure dependence of magnetization below 60 K up to 1.6 GPa in the low-carrier concentration system CeP showing two step transitions at T = T L and T H under high pressure. At high pressure, M ( P , T ) exhibits a maximum at around the lower transition temperature T L . This behavior implies that the magnetic state changes at T L . The pressure dependence of isothermal magnetization M ( P ) is different above and below T L . In fact, M ( P ) below T L exhibits a maximum at around 1.4 GPa, whereas M ( P ) above T L increases steeply with pressure up to 1.6 GPa.

Effect of pressure on crystal field splitting in CeP

Abstract Magnetic properties of CeP at high pressure have been investigated by the measurement of magnetization up to 1.6 GPa. The present result shows the gradual increase of the paramagnetic susceptibility, χ ( T ) and the steep raise of the magnetic transition temperature with increasing pressure. The pressure dependence of χ ( T ) indicates that the contribution of the crystal field at low temperatures was strongly affected by applied pressure. The behaviour of χ ( T , P ) has been analysed by using the crystal field splitting energy and the exchange interactions as the fitting parameters.