Magnetic Resonance of Lanthanide Ions as Magnetic Probes in the Antiferromagnetic Phase of Dysprosium Phosphate

Measurements of electron magnetic resonance are discussed for impurity ions in the antiferromagnetic host compound DyPO₄ (Neel temperature T_N = 3.39 K). This is a simple two sublattice antiferromagnet; the impurity ions are Yb³⁺ and Er³⁺, each with a Kramers doublet as the ground state. Resonance is observed at frequencies of ca. 24 and 34 GHz, and the angular dependence of the magnetic field is fitted to simple theoretical equations. Since the magnetic moments in the host lattice are ordered, the resonance lines are relatively narrow, making it possible to determine the value of the internal field acting on each impurity ion. From this, the exchange field is obtained by subtracting the value of the dipolar field generated by the ordered moments of the host ions. Some measurements have been made in the spin flop phase. The values of the exchange field are found not to conform to a simple model based on isotropic exchange interaction between the real electron spins of the lanthanide ions. Hyperfine splitting is detected from the odd isotope ¹⁷¹Yb, natural abundance 14%, I = 1/2.