Antiferromagnetic Resonance in NiCl26H2O

Abstract

Antiferromagnetic resonance in NiCl ₂ 6H ₂ O was investigated experimentally in the frequency range from 24 to 90 Gc/sec at liquid helium temperature using pulsed magnetic fields. The critical field H _c was determined to be 40±1 kOe. The orthorhombic anisotropy fields H _{A 1} , H _{A 2} and the exchange field H _E were found to be H _{A 1} =9.5±0.5, H _{A 2} =12.5±0.5 kOe, and H _E =86±1 kOe by extending the theory of antiferromagnetic resonance to the strong anisotropy case. The anisotropy comes mainly from the crystalline field constants D and E which were estimated at -1.2cm ^-1 and 0.15 cm ^-1 , respectively. It was found that the spin easy axis is in the ac-plane and differs by an angle 7° from the a-axis. A very broad paramagnetic resonance was observed at 80°K. The origin of this broad line was attributed to the exchange mixing of several paramagnetic resonance lines.