Antiferromagnetic resonance in the canted phase of : Experimental evidence against electronic phase separation

¹ General Physics Institute of the Russian Academy of Sciences 38 Vavilov St., 117942 Moscow, Russia
² Experimentalphysik V, EKM, Universität Augsburg - 86135 Augsburg, Germany
³ Moscow Power Engineering Institute 14 Krasnokazarmennaya St., 105835 Moscow, Russia

Received: 14 October 1999
Accepted: 1 December 1999

Abstract

Antiferromagnetic resonance (AFMR) experiments were performed in single crystals for Sr concentrations . A quasi-optical technique was employed in a frequency range and for temperatures . Two AFMR modes, a quasi-ferromagnetic (F) and a quasi-antiferromagnetic (AF) mode, were observed for temperatures below . The resonance frequency of the F-mode reveals a strong concentration dependence, while the AF-mode frequency only slightly decreases on increasing x. The observed concentration dependencies, as well as the excitation conditions for both modes, can be explained using a simple two-sublattice model. These experiments provide direct evidence in favour of a canted antiferromagnetic (CA) structure for x < 0.1 and low temperatures and cannot be interpreted in terms of a phase separation of ferromagnetic droplets in an antiferromagnetic matrix.