Masayuki Hagiwara

We developed a metallic pressure cell made of 56Ni–40Cr–4Al (Ni–Cr–Al) alloy for use with a non-destructive pulse magnet and a magnetic susceptibility measurement apparatus with a proximity detector oscillator (PDO) in pulsed magnetic fields of up to 51 T under pressures of up to 2.1 GPa. Both the sample and sensor coil of the PDO were placed in the cell so that the magnetic signal from Ni–Cr–Al would not overlay the intrinsic magnetic susceptibility of the sample. A systematic investigation of the Joule heating originating from metallic parts of the pressure cell revealed that the increase in sample temperature is negligible at 1.4 K in magnetic fields of up to 40 T in the field-ascending process for the maximum applied magnetic field of 51 T. The effectiveness of our apparatus was demonstrated by investigating the pressure dependence of the magnetization process of the triangular-lattice antiferromagnet Ba3CoSb2O9.

In this study, magnetostriction measurements were performed on the ferromagnetic Heusler alloy, Ni2MnGa0.88Cu0.12, which is characterized by the occurrence of the martensitic phase and ferromagnetic transitions at the same temperature. In the austenite and martensite phases, the alloy crystallizes in the L21 and D022-like crystal structure, respectively. As the crystal structure changes at the martensitic transition temperature (TM), a large magnetostriction due to the martensitic and ferromagnetic transitions induced by magnetic fields is expected to occur. First, magnetization (M-H) measurements are performed, and metamagnetic transitions are observed in the magnetic field of μ0H = 4 T at 344 K. This result shows that the phase transition was induced by the magnetic field under a constant temperature. Forced magnetostriction measurements (ΔL/L) are then performed under a constant temperature and atmospheric pressure (P = 0.1 MPa). Magnetostriction up to 1300 ppm is observed around TM. The magnetization results and magnetostriction measurements showed the occurrence of the magnetic-field-induced strain from the paramagnetic austenite phase to the ferromagnetic martensite phase. As a reference sample, we measure the magnetostriction of the Ni2MnGa-type (Ni50Mn30Ga20) alloy, which causes the martensite phase transition at TM = 315 K. The measurement of magnetostriction at room temperature (298 K) showed a magnetostriction of 3300 ppm. The magnetostriction of Ni2MnGa0.88Cu0.12 is observed to be one-third that of Ni50Mn30Ga20 but larger than that of Terfenol-D (800 ppm), which is renowned as the giant magnetostriction alloy.