Mössbauer Study of a Random Mixture with Orthogonal Spin Anisotropies: Rb₂Co_1-<i>x</i>Fe_<i>x</i>F₄

Abstract

Mössbauer spectroscopy has been used to study the magnetic properties of a two-dimensional (2 D ) random mixture Rb 2 Co 1- x Fe x F 4 with competing spin anisotropies. The direction of individual Fe spin has been shown to be tilted in both the antiferromagnetic (AF) and mixed ordering phases. This means that, in the AF phase, the spin component which has no long-range order exists statically at least in the time scale of the Larmor precession of 57 Fe (∼10 -8 s) and couples to the other spin component which exhibits a long-range order. The behavior of individual Fe spin is different from that in the other mixtures (1 D and 3 D systems). In the sample of x =0.81, with decreasing temperature, Fe spins fall down successively from a direction almost parallel to the c -axis to the direction which makes an angle of ∼70^° with the c -axis. This phenomenon is probably connected with a change from 2 D order into 3 D order of the spin system.