Field-Dependent Magnetic Susceptibility of MnO

The field dependence of the magnetic susceptibility of MnO powder has been studied in continuous fields up to 50 kOe, between 4.2° and 200°K. Each isotherm is measured from a virgin magnetic state to avoid hysteresis and viscosity complications. Above the antiferromagnetic Néel point, the susceptibility is field independent with a maximum value of (83±1)×10−6 emu/g at 122°K. At 4.2°K, the susceptibility saturates with field at a value of 79×10−6 emu/g. This is identified as the transverse susceptibility. It drops slightly with temperature to a broad minimum at 55°K. An attempt to analyze the field dependence using the model of Keffer and O'Sullivan suggests that the weak in-plane anisotropy, K2, has orthorhombic symmetry. This model is rejected because it ignores domain wall displacement. A rough estimate of K2 at 4.2°K is 9×103 erg/cc, assuming trigonal symmetry.