Magnetic Susceptibility and Specific Heat of an Anisotropic Spin-Glass:EuxSr1−xAs3

The magnetic susceptibility of ${\mathrm{Eu}}_x{\mathrm{Sr}}_{1-x}{\mathrm{As}}_3$ spin-glasses is highly anisotropic: For $x=0.24\mathrm{}$ and $x=0.3\mathrm{}$ the longitudinal and transverse susceptibilities (with respect to the orientation of magnetic moments in antiferromagnetic Eu${\mathrm{As}}_3$) exhibit spin-glass-like maxima at different temperatures, with the longitudinal freezing occurring at higher temperature. The magnetic specific heat displays a temperature dependence not previously found in spin-glasses, $C_M=aT \exp (-\frac{\Delta E}{k_{\mathrm{B}}T})$. This indicates a gap around zero energy in the density of states of magnetic excitations, which arises from the anisotropy.