Nonresonant microwave absorption in epitaxialLa0.7Sr0.3MnO3films and its relation to colossal magnetoresistance

Abstract

We study magnetic-field-dependent nonresonant microwave absorption and dispersion in thin La 0.7 Sr 0.3 MnO 3 films and show that it originates from the colossal magnetoresistance. We develop the model for magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The model accounts fairly well for our experimental findings, as well as for results of other researchers. We demonstrate that nonresonant microwave absorption is a powerful technique that allows contactless measurement of magnetic properties of thin films, including magnetoresistance, anisotropy field and coercive field.

Magnetization dynamics in La0.67Ca0.33MnO3 epitaxial films probed with resonant and non-resonant microwave absorption

“…This behaviour is consistent with the results of magnetoresistance measurements in epitaxial films of manganites. 8 However, as the film thickness reduces, the magnetic transition temperature goes down and the ordered moment grows gradually on lowering the temperature as seen in Fig. 6(b).…”

“…As shown in Ref. 13, for dc field aligned parallel to film normal, the spin wave modes are given by;…”

“…The manganites like La 0.70 Ca 0.30 MnO 3 show a colossal negative magnetoresistance effect due to double exchange mechanism between Mn 3þ and Mn 4þ ions through the bridging oxygen, which also facilitates ferromagnetic ordering. It has been shown earlier by Golosovsky et al 8 that the change in conductivity due to CMR effect can be expressed as;…”

“…Here, the EPR technique established coexistence of two ferromagnetic phases of widely differing T C . The intrinsic magneto-resistance (MR) in La 0.7 Ca 0.3 MnO 3 films and its dependence on the angle between magnetic field and crystallographic axis have been studied by Golosovsky et al 8 Since in many potential applications the manganites would be used in a thin film form, it is important to establish how the relative phase content and thus the electro-magnetic response will be affected by film thickness, choice of the substrate and growth temperature. Even though quite a few studies have been carried out to explore the magnetic properties of manganites using FMR, a comparison of how FMR and EPR spectra evolve as a function of film thickness and magnetic field orientation still need to be addressed.…”

“…6 While several probes have been used to study phase separation in manganites, the coexisting of various ferromagnetic, paramagnetic and antiferromagnetic phases, their anisotropies and the dynamics of magnetization can be addressed in a rigorous manner using the electron spin resonance (EPR) technique. [7][8][9][10][11][12][13] For example, Tovstolytkin et al 7 have used EPR to investigate the complex phase separation in La 0.6 Ca 0.4 MnO 3 films grown on NdGdO 3 (001) under specific condition. Here, the EPR technique established coexistence of two ferromagnetic phases of widely differing T C .…”