Hidenori Miyagawa

Magnetoresistance of CePtSi2 under high pressure

The electrical resistivity and magnetoresistance (MR) of CePtSi2 have been measured under high pressure in order to clarify the electronic state around T N ∼ 0 K. ρmag (T) at ambient pressure, defined as ρmag = ρ(CePtSi2)−ρ(LaPtSi2), increases with decreasing temperature until it shows a maximum around 28 K(=T 2) and a small shoulder around 5 K(=T 1). T 1 increases with applying pressure and merges into T 2 around 1.0 GPa. T 2 is almost constant up to 1.0 GPa, but increases rapidly with applying pressure above 1.0 GPa. Negative MR was observed up to 2.4 GPa at 4.2 K. The magnitudes of MR at 9 T are−24.5% and−7.9% at 0.1 and 2.4 GPa, respectively. By applying the Okiji–Kawakami model to the present results, it is found that the Kondo temperature T K increases with increasing pressure. The slope of pressure dependence of MR ratio at 9 T changes slightly around 1.0 GPa. These results suggest a pressure-induced crossover in the electronic states around 1.0 GPa.

Hall effect in CeAl2 under high pressure

We have measured the Hall effect of the single crystalline CeAl2 under high pressure up to 3 GPa. An anomalous Hall effect was observed at high pressures. The Hall coefficient RH at 0.1 GPa is positive (RH ~ 1.7×10−9 m3/As). It decreases smoothly with increasing pressure below 2 GPa, but rapidly above 2 GPa. The sign of the Hall coefficient is found to change from positive to negative as pressure increases. These results suggest a pressure-induced crossover in the electronic state around 2.7 GPa.

Synthesis of Heavy Fermion Ce Compound under High Pressure

CeCu 6 is well known as a typical heavy fermion compound and prepared at ambient pressure by melting γ-Ce and Cu. We attempted to prepare a new type of CeCu 6 by melting α-Ce and Cu under high pressure using the characteristic pressure–temperature phase diagram of Ce. The samples were prepared at high pressure and high temperature. The electrical resistance and specific heat were measured. It is found that the temperature dependence of the electrical resistance of newly prepared CeCu 6 (α-CeCu 6 ) shows a similar behavior as CeCu 6 prepared at ambient pressure and high temperature although with a difference at low temperature below 30 K. According to the result of specific heat, it is suggested that α-CeCu 6 is in the heavy fermion state.