Magnetic properties of various martensitic phases in Ni-Mn-Ga alloy

Single crystalline Ni48.7Mn29.1Ga22.2 sample was studied in the temperature range 110 K-425 K. Magnetic properties of four different structure phases were measured at different temperatures. The magnetic anisotropies of the different phases were determined from magnetization curves. At room temperature, the structure is five-layered modulated tetragonal martensite with c/a < 1 and uniaxial anisotropy K-u1 = 1.6 x 10(5) J(.)m(-3). Below 251 K, the structure is orthorhombic c < b < a with c being easy magnetization axis. The magnetic anisotropy energy is 2.1 x 10(5) J.m(-3) between c and a. At 218 K, the orthorhombic phase transforms to tetragonal phase with c/a > 1. Single variant of low-temperature martensite was obtained by cooling in magnetic field 1.4 T. At 173 K, the sum of magnetic anisotropy constants is K-1 + K-2 = 1.5 x 10(5) J.m(-3) assuming the easy-piane magnetic anisotropy.