Optical study of the spontaneous magnetization at marginal dimensionality

The spontaneous magnetization in the critical region of the uniaxial, dipolar-coupled ferromagnet LiTbF₄ has been measured using sensitive optical techniques. The magnetic and optical properties of LiTbF₄ and the experimental techniques are discussed in detail. These measurements provide a quantitative comparison between the predicted logarithmic corrections to mean-field theory and the experimentally observed magnetization of a ferromagnet at marginal dimensionality. We conclude that the spontaneous magnetization in LiTbF₄ is described by the relation Mc(T)Mc(T=0)=B|t|1/2|ln|t₀t||1/3 over the range $0.002<~t<~0.09$ with B=1.77±0.06, Tc=2.8700±0.002 K and t₀=0.53±0.06.