Effect of a Magnetic Field on Susceptibility of a Two-Dimensional Ferromagnet K₂Cuf₄ Near the Curie Temperature

The magnetic susceptibility χ_a in the two-dimensional ferromagnet K₂CuF₄ has been measured near T_c = 6.25 K with the magnetic field H applied in the direction parallel to the a -axis in the easy plane. The field and temperature dependences of χ_a are determined and the static scaling hypothesis is examined. Above T_c, it is found that χ_a is described by a scaling function, (formula omitted), where t =|T/T_c -1|, λ=0.82 ±0.05 and µ=0.83 ±0.05. The critical exponents of magnetization and susceptibility, β and γ, are estimated as β=0.22 ±0.05 and γ=0.99 ±0.05 from the relations β=(1 -λ)/µ and γ=λ/µ. The susceptibility χ_a has a broad peak in an external magnetic field above T_c which shifts to higher temperatures as the mannetic field increases. This broad peak corresponds to the appearance of the magnetic-field-induced ferromagnetic state.