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In ferromagnetic CdCr2Se4 diluted with Mex3+ = In and Sb, deviations from cubic symmetry appear in the paramagnetic phase just below room temperature, and they increase with decreasing temperature. For Sb admixture, the unit-cell anomalies indicate a structural phase transition to occur at the same temperature as the magnetic transition, Tc = 130 K, which also is the same Tc as for the parent crystal CdCr2Se4. The low temperature phase has been described in orthorhombic space group Fddd. For In admixture, a structural transition occurs in the paramagnetic state at about Ta≈200 K (which is higher than Tc = 125 K), to a tetragonal structure with space group I41/amd. This behaviour is attributed to macroscopic spontaneous strain due to chemical heterogeneities, and to spin frustrations due to mixed valencies of Cr. The paramagnetic Curie–Weiss temperature θC−W decreases for both admixtures, indicating changes in competing ferromagnetic and antiferromagnetic interactions. The magnetization at 2.1 K exhibits saturation for H>0.6 T. The magnetic moments are μsat = 6.26 and 5.47 μB mol−1 for Sb and In admixtures, respectively. These values are consistent with the Cr3+ and Cr2+ mixed valencies, and with the proposed cation distribution model. A spin–phonon coupling of the transitions in the crystal with Sb admixture is suggested, while such a correspondence is not clear for the In admixture.

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We used molecular beam epitaxy to deposit a novel ferro-/antiferromagnet (Fe/KCoF3) system on gallium terminated GaAs (100) substrates. We varied the thicknesses of single crystal Fe (001) layers from 1.05 to 3 nm. The antiferromagnetic fluoride, with a thickness of 30 nm, was deposited either in a single-crystal or a polycrystalline form, depending on the deposition conditions. KCoF3 is an antiferromagnet with a Néel temperature of 114 K. Its cubic structure almost perfectly matches the Fe film structure. The growth was monitored by reflection high energy electro diffraction. The magnetic properties of the system were studied using ferromagnetic resonance. Uniaxial and unidirectional anisotropy fields, due to exchange bias, were measured at low temperatures in the field-cooled samples and were smaller than 45 and 72 Oe, respectively. Both anisotropy fields, unidirectional and uniaxial, decreased with increasing thickness of the Fe film or with increases in temperature. The temperature dependence of the fourfold anisotropy was studied for the samples with different thicknesses of Fe films and different crystalline states of the fluoride layer. Room temperature values of the fourfold anisotropy also increased with increasing thickness of the Fe layer and were in a fairly good agreement with previously reported values for single crystal Fe films. Also, the temperature characteristics of the fourfold anisotropy for the structures with single crystal fluoride seemed to reproduce low-temperature literature data for Fe (001) films. In contrast, the structures with polycrystalline KCoF3 demonstrated a significant enhancement of the fourfold anisotropy at low temperatures. For the thinnest sample (tFe=1.05 nm) the low temperature anisotropy is more than tripled compared to room temperature values. It is believed that the surface effects can be responsible for this enhancement.