Abstract
Antiferromagnetic resonance (AFMR) experiments were performed in La1 − xSrxMnO3 single crystals for Sr concentrations 0 ⩽ x ⩽ 0.1. A quasi-optical technique was employed in a frequency range 2 cm−1 < ν < 30 cm−1 and for temperatures 3 K < T<300 K. Two AFMR modes, a quasi-ferromagnetic (F) and a quasi-antiferromagnetic (AF) mode, were observed for temperatures below TN. 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.