Single domain behaviour of bulk RbMnF3

Abstract

The temperature dependence of the order parameter of antiferromagnetic RbMnF3 has been measured using neutron scattering. After necessary corrections, single crystal data agree perfectly with data obtained on powder material. Surprisingly, the order parameter of cubic RbMnF3 exhibits the same universal T5/2 temperature dependence as the order parameter of tetragonal MnF2. T5/2 universality class has been identified as characteristic for magnets with one-dimensional continuous dynamic symmetry. It is discussed in some generality that the domain structure is decisive for the dynamic symmetry class. If powder grains are single domain particles one-dimensional behaviour can be anticipated generally. However, bulk single crystals of cubic RbMnF3 should be in the multi-domain state and should exhibit the T2 universality class of isotropic magnets with half-integer spin. Isotropy results by a dynamic averaging process over all differently oriented magnetic domains. Since the magneto-elastic coupling of RbMnF3 is extremely weak it can be assumed that the domain structure is rather coarse. If the domain size is larger than the dynamic length scale of the order parameter the usual averaging process over all domain orientations does not work. Consequently, the observed one-dimensional continuous dynamic symmetry of bulk RbMnF3 is that of an isolated domain.