Invariants in the paramagnetic resonance spectra of impurity crystals

TL;DR

This paper demonstrates an invariant property of EPR spectra in cubic crystals with impurity centers, linking it to the g-tensor, and confirms it experimentally, aiding in paramagnetic center identification.

Contribution

It introduces a new invariant in EPR spectra of impurity centers in cubic crystals and connects it to g-tensor components, with experimental validation.

Findings

Sum of squares of EPR frequencies is invariant with magnetic field orientation.

The invariant relates to the g-tensor components of impurity centers.

Experimental confirmation using CaF2-Nd3+ crystal spectra.

Abstract

We show that in cubic crystals with anisotropic impurity centers the sum of squares of the magnetic resonance (EPR) frequencies is invariant with respect to the magnetic field direction. The connection between such an invariant and the g-tensor components of the impurity is derived for different types of centers. The established regularity is confirmed experimentally for the spin-noise spectra of a CaF2-Nd3+ crystal. We show how this property of the EPR spectra can be efficiently used for the assignment of paramagnetic centers in cubic crystals.