Bulk and surface spin excitations in thin films of manganites

Abstract

A review of experimental studies of magnon excitations in manganites is presented. A microwave resonance technique, in particular a spin‐wave resonance (SWR) technique, is shown to allow the study of not only bulk properties but also surface properties of manganite films. There are two main theoretical approaches used to interpret the SWR spectra: the volume inhomogeneity and the surface inhomogeneity models. The latter, introduced by Puszkarski, allows the interpretation of the observed surface magnon excitations in thin films. It is found that SWR spectra show evidence of manganites, besides bulk spin‐wave modes, and also of surface spin‐waves. This observation is used to determine the surface magnetic anisotropy. The effect of surface anisotropy on the spin‐wave excitation conditions in epitaxial La0.7Mn1.3O3–δ films is investigated in detail. SWR data give indirect evidence of periodic charge‐ordered stripe forma‐tion. A strong effect of thermal annealing on stripe structure is observed and discussed. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spin-wave resonances inLa0.7Sr0.3MnO3films: Measurement of spin-wave stiffness and anisotropy field

“…Contrary to Ref. [17] we found that oxygen annealing at different temperatures from 600 0 C to 900 0 C does not ameliorate the SWR spectrum in our films but introduces additional splitting. In particular, the resonant peaks in annealed films split into many narrow lines with the spacing of ∼15 Oe.…”

“…The difference between our results and those of Ref. [17] is probably related to the fact that we operate with the film of different composition and on different substrate. …”

“…(9) [14,15,16,17,18,19,20] and present work). The x ∼ 0.3 composition corresponds to highest conductivity and is the most distant from phase boundaries, [50] in other words, the phase separation effects should be least insignificant here.…”

“…We attribute the peak at 7470 Oe to the region with a different discrete value of the anisotropy field and exclude it from the subsequent analysis. [17] we studied the effect of oxygen annealing on the SWR spectra in our films. Contrary to Ref.…”

“…[14]), and La 0.7 Mn 1.3 O 3 (Refs. [15,16,17]) thin films. Although spin-wave excitation at microwave frequencies was observed in La 0.75 Sr 0.11 Ca 0.14 MnO 3 (Ref.…”