The Co-doped Tb_0.36Dy_0.64Fe₂ magnetostrictive alloys with a wide operating temperature range

Magnetostrictive alloys with a wide operating temperature range from -80 to 150 °C were developed by changing the Tb/Dy ratio of Tb_xDy _1-xFe₂ from 0.3/0.7 to 0.36/0.64 and Co partly substituting for Fe. The structure, Curie temperature, AC susceptibility, magnetization, magnetocrystalline anisotropy constant K₁ and magnetostriction of Tb_0.36Dy_0.64(Fe_{1- y}Co_y)₂ (y=0.0, 0.1, 0.2) alloys were investigated. It was found that the matrix of Tb_0.36Dy _0.64(Fe_1-yCo_y)₂ alloys keeps the MgCu₂-type cubic Laves structure with a small amount of R-rich phase. A small amount of R₂(Fe,Co) phase was also detected when y=0.2. The Curie temperature T_c of Tb_0.36Dy _0.64(Fe_1-yCo_y)₂ alloys is higher than Tb_0.3Dy_0.7Fe₂ and increases drastically with increasing Co content from 387.1°C for Tb _0.36Dy_0.64Fe₂ to 416.7°C for Tb _0.36Dy_0.64(Fe_0.9Co_0.1)₂ and 433.3°C for Tb_0.36Dy_0.64(Fe_0.8Co _0.2)₂. The spin reorientation temperature T_r decreases from -12°C for Tb_0.3Dy_0.7Fe₂ to -94°C for Tb_0.36Dy_0.64Fe₂. It increases slightly with increasing Co content. The magnetocrystalline anisotropy coefficient K₁ of Tb_0.36Dy_0.64(Fe _1-yCo_y)₂ alloys is greater than Tb_0.3Dy_0.7Fe₂ but decreases with increasing Co content. The saturation magnetization M_s of Co-doped alloys is lower than that of Tb_0.3Dy_0.7Fe₂ and decreases with increasing Co content. The magnetostriction of Tb_0.3Dy _0.7Fe₂ and Tb_0.36Dy_0.64(Fe _1-yCo_y)₂ alloys was examined against applied magnetic field up to 5 kOe in the temperature range from -80 to 150°C.The temperature coefficient of magnetostriction (Δλ/ ΔT) of Tb_0.3Dy_0.7Fe₂ and Tb _0.36Dy_0.64(Fe_1-yCo_y) ₂ alloys was also calculated by linearly simulating the magnetostriction-temperature curve, showing that the absolute value of Δλ/ΔT at 5 kOe magnetic field is 1.17 ppm/°C for y=0.1 and 1.35 ppm/°C for y=0.2, smaller than that of Co free samples, which is 2.43 ppm/°C for Tb_0.36Dy_0.64Fe₂.