Antiferromagnetic resonance in the canted phase of La _{1 − x} Sr _x MnO ₃ : Experimental evidence against electronic phase separation

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.

Anisotropy of magnetic properties in LaMnO3 single crystals

“…The obtained data are in qualitative agreement with the results of previous studies [1][2][3][5][6][7]; some discrepancies may arise because of a small difference in cation and oxygen stoichiometries. The present results confirm existence of canted magnetic structure A a F b type in LaMnO 3 .…”

Magnetic ground state of low-doped manganites probed by spin dynamics under magnetic field

“…On the other hand, in case (ii), the superposition of two spin excitation spectra is expected, a doubly degenerate AF branch for the AF matrix, superposed on a F branch for F domains, giving rise to three branches under applied field. RPE experiments [4,5], which probe the q ¼ 0 modes under applied field, determine two spin wave excitations with F and AF character, in agreement with the case (i). Neutron scattering [6,7] which measures the full q-dependence, reveals additional features, distinct from mean field calculation, leading to a third picture of a modulated canted AF ground state.…”

“…Neutron scattering [6,7] which measures the full q-dependence, reveals additional features, distinct from mean field calculation, leading to a third picture of a modulated canted AF ground state. The two branches, one at high energy, observed around the AF zone centers, the other, at lower energy, observed around the F ones, do not cross each other, as expected in case (i), but lie in separated energy ranges along c. An elastic diffuse neutron scattering [4] indicates nanosize ferromagnetic inhomogeneities, with the same magnetization direction. A direct relation between the F branch and the F inhomogeneities is observed through their q-dependent intensity.…”

Approach to the metal-insulator transition inLa1−xCaxMnO<

“…These non-linear features with x, observed both at q = 0 and at q = 0, disagree with the usual picture of a meanfield canted state. At q = 0, a monotonous decrease of the large anisotropy gap, Ω 0 , associated with the antiferromagnetic structure, is expected 33 , instead of an x-independent behaviour. Moreover, in such a model, the two spin-wave branches would cross each other along [001] at q = (0, 0, 1.5), instead of keeping in separated energy range as shown in Fig.…”