Logarithmic Corrections in the Magnetic Equation of State for LiTbF4

Using SQUID (superconducting quantum interference device) detection, the field and temperature dependence of the magnetization $m$ has been measured close to the critical point of this uniaxial dipolar-coupled ferromagnet. It is shown for the first time that the Landau expansion of the field $h$ holds if $m$ is scaled by ${\left[\frac{\ln \left(\frac{\partial m}{\partial h}\right)}{{\chi }_0}\right]}^{\frac{1}{3}}$, while other equations (of Ising, mean field) yield less agreement and unrealistic parameters. The expansion coefficients of the present analysis can explain in detail formerly measured zero-field properties.