Antiferromagnetic Resonance in NiCl₂6H₂O

Abstract

Antiferromagnetic resonance in NiCl₂6H₂O 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_A1, H_A2 and the exchange field H_E were found to be H_A1=9.5±0.5, H_A2=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.