Spin glass phenomena in TbFe_xAl_12-x

Magnetization and ⁵⁷Fe Mössbauer spectroscopy measurements of TbFe_xAl_12-x (x = 3.5,4,4.5,5,5.5,6) at temperatures 4.2 to 350 K have been performed. The Mössbauer studies yield the iron relative occupation of the three, (f), (j) and (i), inequivalent crystallographic sites in the tetragonal (I4/mmm) unit cell, their hyperfine field distributions and the magnetic ordering temperatures. These are quite similar to those previously reported for YFe_xAl_12-x. The magnetization measurements, however, display quite different phenomena than those observed for YFe_xAl_12-x. The contribution of the Tb sublattice to the magnetization with its associated high magnetic anisotropy and the spin glass structure in the iron sublattices lead to the wide variety of unusual phenomena observed. These include: negative magnetization at low temperature when the sample is cooled in a magnetic field (TbFe₅Al₇). Three maxima in the magnetization temperature dependence of TbFe_4.5Al_7.5. Differences in magnetization curves depending on cooling rates. The more common phenomena associated with the spin glass structure, namely, differences between field cooled and zero field cooled magnetization curves, thermoremanent and isothermal remanent magnetization and their time dependences were also observed.