Magnetization and Phase Transitions in Single-Crystal Tb$_5$(Si$_{2.2}$Ge$_{1.8}$)

The Tb$_{5}$(Si$_{x}$Ge$_{4-x})$ alloy system is similar to the Gd$_{5}$(Si$_{x}$Ge$_{4-x})$ system although it has a more complex magnetic and structural phase diagram. We report on the magnetic anisotropy and magnetic phase transitions in single crystal Tb$_{5}$(Si$_{2.2}$Ge$_{1.8})$ by measurements of M-H and M-T along the a, b, and c axes. The variation of 1/$\chi $ vs T indicates a transition from paramagnetic to ferromagnetic at T$_{c}$ = 110 K. Below this transition temperature, M-H curves show strong anisotropy. It is believed this is due to the complex spin configuration. M-H measurements at T = 110 K show that the \textbf{\textit{a }}axis is the easy axis, and that the saturation magnetization is 200 emu/g. The $b$ axis is the hard axis, which needs an external magnetic field higher than 2 T to saturate the magnetization in that direction, indicating a high magnetocrystalline anisotropy. The c axis is of intermediate hardness. This research was supported by the U.S. Department of Energy under contract number W-7405-ENG-82.