Cobalt-Doped TlMnF3, a Zero Anisotropy Cubic Antiferromagnet

Abstract

Single crystals of cobalt-doped thallium manganese fluoride (TlMn1−xCoxF3) have been studied by antiferromagnetic resonance for cobalt concentrations of 0≤x≤0.001. In this range the antiferromagnet remains cubic at 4.2°K, with its crystalline anisotropy varying linearly with cobalt concentration from K1/M = −5.1 Oe for pure TlMnF3 to +8.2 Oe, passing through zero for x=0.0004. Other magnetic properties, such as Néel temperature and exchange field, are unaffected by the small cobalt concentrations. Multiple non-equivalent equilibrium spin-orientation states, which have been observed in spin-flopped resonance in the 〈100〉 and 〈110〉 crystal planes when K1/M is greater than zero, are described.