The Co-doped Tb0.36Dy0.64Fe2 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 TbxDy1−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 Tb0.36Dy0.64(Fe1−yCoy)2 (y=0.0, 0.1, 0.2) alloys were investigated. It was found that the matrix of Tb0.36Dy0.64(Fe1−yCoy)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 Tc of Tb0.36Dy0.64(Fe1−yCoy)2 alloys is higher than Tb0.3Dy0.7Fe2 and increases drastically with increasing Co content from 387.1 °C for Tb0.36Dy0.64Fe2 to 416.7 °C for Tb0.36Dy0.64(Fe0.9Co0.1)2 and 433.3 °C for Tb0.36Dy0.64(Fe0.8Co0.2)2. The spin reorientation temperature Tr decreases from −12 °C for Tb0.3Dy0.7Fe2 to −94 °C for Tb0.36Dy0.64Fe2. It increases slightly with increasing Co content. The magnetocrystalline anisotropy coefficient K1 of Tb0.36Dy0.64(Fe1−yCoy)2 alloys is greater than Tb0.3Dy0.7Fe2 but decreases with increasing Co content. The saturation magnetization Ms of Co-doped alloys is lower than that of Tb0.3Dy0.7Fe2 and decreases with increasing Co content. The magnetostriction of Tb0.3Dy0.7Fe2 and Tb0.36Dy0.64(Fe1−yCoy)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 Tb0.3Dy0.7Fe2 and Tb0.36Dy0.64(Fe1−yCoy)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 Tb0.36Dy0.64Fe2.