SH³ Term in the Submillimeter Electron Spin Resonance of Cobalt Tutton Salt

Abstract

Submillimeter ESR in cobalt ammonium Tutton salt (NH₄)₂Co(SO₄)₂·6H₂O was studied at liquid nitrogen temperature using pulsed high magnetic fields and two submillimeter waves, 337 μm of HCN laser and 119 μm of H₂O laser. The frequency dependence of the g value was observed. For example, g_|| at 119 μm was about 2% smaller than that at 337 μm. The observed frequency dependence can be explained by introducing a new SH³ term in the effective spin Hamiltonian. An extensive theoretical consideration based on the Abragam-Pryce theory shows that the observed shift can satisfactorily be explained quantitatively. This is the first experimental observation of SH³ term of the iron group ions in ionic crystals.