HoFe4Al8: An unusual spin glass

We report on the spin-glass behavior of ${\mathrm{HoFe}}_4$ ${\mathrm{Al}}_8$. Irreversible and time-dependent effects in the intensities of magnetic Bragg scattering derived from neutron diffraction reveal this behavior pronouncedly below $T_{\mathrm{SG}=180\mathrm{}}$ K. Further evidence comes from the dc isothermal and thermoremanent magnetization. The Mössbauer ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ spectra show a sudden onset of magnetic hyperfine splitting below $T_{\mathrm{SG}}$ and a flat temperature dependence together with irreversible effects under applied magnetic fields. A transition temperature from aligned to random spin-glass states $T_{\mathrm{OG}}$, is reported. $T_{\mathrm{OG}=40\mathrm{}–}$70 K, depending on the applied magnetic field. Most unusual is the lack (or extremely broad) of a cusp in the ac susceptibility in the vicinity of $T_{\mathrm{SG}}$.