Frustration effects in the disordered system CsMnFeF6, studied by neutron scattering, ac susceptibility, and magnetization measurements

In CsMnFeF6, which has a cubic structure (a=10.5), space group Fd3m, the magnetic ions Mn2+ and Fe3+ form regular tetrahedra. The system should exhibit frustration effects, since the nearest-neighbor interactions are antiferromagnetic in character. We performed neutron scattering, ac susceptibility, and magnetization measurements both on a powder and a single crystal, for temperatures 1.2300 K and applied magnetic fields 50 kOe. It was found that already at T=300 K there are well-developed clusters of antiferromagnetically coupled spins. These clusters have a weak resulting moment. Lowering the temperature to T80 K leads to an increase of the effective moment due to the reduction of the thermal motions, whereas this moment remains constant for T80 K. At T=26.3 K the cluster moments freeze in a process which is accompanied by a ferromagnetic ordering of the resulting moments of the clusters. It is suggested that an applied magnetic field breaks the large domains, containing many clusters, into microdomains containing only a few clusters, or even one.