Spin-Flopping in MnF2 by High Magnetic Fields

Observations of spin-flopping, or decoupling between the direction of antiferromagnetism and the easy axis of the crystal, are presented for ${\mathrm{MnF}}_2$ in single crystal and powder form at low temperatures. Magnetization measurements in pulsed fields to 140 koe are employed to explore the critical interaction energy in this antiferromagnet, as an alternative tool to microwave resonance. The orientation dependence predicted by Néel in 1936 is confirmed. The critical field for spin-flopping given by the combination of anisotropy and exchange, ${\text{(2H}}_E{H}_A{)}^{\frac{1}{2}}$ is found to be 93±2 koe in excellent agreement with resonance results of S. Foner [(a) Phys. Rev. 107, 683 (1957); (b) J. phys. radium 20, 336 (1959)], and F. M. Johnson and A. H. Nethercot [Phys. Rev. 104, 847 (1956); 114, 705 (1959)].