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The electrical resistivity and magnetoresistance (MR) of CePtSi2 have been measured under high pressure in order to clarify the electronic state around TN ∼ 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(=T2) and a small shoulder around 5 K(=T1). T1 increases with applying pressure and merges into T2 around 1.0 GPa. T2 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 TK 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. [ABSTRACT FROM AUTHOR]

Abstract: The influence of pressure on the formation of U magnetic moments and mediation of exchange interactions are two principal aspects of the complex role of the 5f-ligand hybridization in magnetism of U intermetallics. Application of external pressure yields changes of interatomic distances, which are the crucial parameters controlling the hybridization. We report on pressure experiments with a 5f-electron ferromagnet UPtAl (T C=42.5K, M s=1.4 μ B/f.u. at ambient pressure). Application of hydrostatic pressure up to 1GPa yields decrease of the spontaneous magnetization M s with a rate dM s/dp=−0.027 μ B/GPa, whereas T C increases (dT C/dp=2.5K/GPa). Extension of the electrical resistivity measurements of UPtAl to pressures up to 22GPa reveals that the initial increase of T C with pressure continues up to 6GPa, where T C reaches the maximum value, and decreases with further increasing pressure. The drastic change of the R(T) curve at 17GPa is presumably connected with suppression of ferromagnetism in UPtAl. [Copyright &y& Elsevier]

• New phase diagram of ferromagnetic shape memory alloy Ni 2+ x MnGa 1− x. • Characteristic composition dependence of phase transitions related to magnetism and structure. • Comprehensive review that includes other representative Ni-Mn-Ga Heusler alloys. [Display omitted] This study experimentally investigates a series of phase transitions of ferromagnetic shape memory alloys, Ni 2+ x MnGa 1− x , in the composition range 0.02 ≤ x ≤ 0.27. An experimental phase diagram of these alloys was constructed by the use of electrical resistivity, thermomagnetization, and thermoanalysis measurements, and compared with both the Ni-rich Ni 2+ x Mn 1− x Ga and Mn-rich Ni 2 Mn 1+ y Ga 1− y alloy systems which have been extensively studied as proto-materials for ferromagnetic Heusler alloys. The comparison makes it clear that there are remarkable composition dependencies for the following characteristic temperatures. All three systems have the common property that Curie temperature decreases and martensitic transition temperature increases with increasing x till the both temperatures coincide each other. As for the magnetostructural coupling temperature, however, the Ni-rich system has a wide temperature range, and the Mn-rich system does not show signs of the magnetostructural coupling, whereas the magnetostructural coupling was observed in Ni 2+ x MnGa 1− x alloys in the range 0.10 ≤ x ≤ 0.12 which has similar characteristics between the former two systems. The premartensitic transition temperature was also observed in Ni 2+ x MnGa 1− x alloys; it reached the ambient temperature at x = ~0.04, the highest of the three alloy systems. In addition, an intermartensitic transition appeared in Ni 2+ x MnGa 1− x alloys in the composition range 0.06 ≤ x ≤ 0.10, which showed a drastic change especially in the electrical resistivity. These characteristic temperatures are also compared in terms of the number of valence electrons among the Ni–Mn–Ga Heusler alloy systems, and the differences are clarified and discussed in detail. [ABSTRACT FROM AUTHOR]

The electrical resistivity of single crystalline CeRh2Si2 has been measured in the temperature range from 2.0 to 300 K under high pressure up to 2.3 GPa. The coefficient of T2 term A(P) and the residual resistivity ρ0(P) have been obtained as a function of pressure. It is found that A(P) shows one maximum and ρ0(P) show two maxima near the pressure where the magnetic ordering phases disappear. The result is discussed on the basis of pressure-induced quantum phase transition. [Copyright &y& Elsevier]