ac susceptibility measurements are presented on the dilute, dipolar coupled, Ising magnet ${\mathrm{LiHo}}_x{\mathrm{Y}}_{1-x}{\mathrm{F}}_4$ for a concentration $x=0.045$. The frequency and temperature dependences of the susceptibility show characteristic glassy relaxation. The absorption spectrum is found to broaden with decreasing temperature suggesting that the material is behaving as a spin glass and not as an exotic spin liquid as was previously observed. A dynamical scaling analysis suggests a spin glass transition temperature of $43\pm 2\mathrm{mK}$ with an exponent $z\nu =7.8\pm 0.2$.

• Received 8 August 2008

DOI:https://doi.org/10.1103/PhysRevLett.101.187204