Magnetic Pseudoresonance in Manganite Thin Films

Abstract

A strong narrow peak in the field dependence of the radio-frequency absorption (the magnetic pseudoresonance) has been found and investigated in epitaxial thin films of La 2/3 Sr 1/3 MnO 3 possessing uniaxial magnetic anisotropy in the film plane. The peak is observed when the in-plane external magnetic field H is directed perpendicular to the easy axis and equals to the anisotropy field H u . The frequency dependence of the peak magnitude measured in the frequency range of 10-300 MHz approximately follows the Debye law behavior with the characteristic relaxation time of about 2.2 ns. The physical model of the phenomenon is suggested, based on the giant increase in static transversal susceptibility due to a sharp reorientation of the equilibrium magnetization when approaching the pseudoresonance conditions.

Ferromagnetic pseudoresonance in anisotropic thin films and its relation to level anticrossing: quantum versus classical

“…absorption was also observed in a series of epitaxial thin films of La 0.7 Sr 0.3 MnO 3 (LSMO) prospective for application in nano-electronics [3]; in this case, the effect was employed for accurate determination of the magnitude and direction of the anisotropy field. In the same material, the Debye-like frequency dependence of the peak magnitude was observed, with the relaxation rate of the order of 10 9 s −1 [4].…”

“…The sample used in our experiments was chosen from the series of LSMO/NGO epitaxial films described in [3,4]. The pseudoresonance feature was observed in all samples of this series.…”

“…Recently, a giant peak of the radio-frequency (r.f.) absorption (the imaginary part of dynamic magnetic susceptibility χ″) was observed in ferromagnetic films which exhibit the in-plane uniaxial magnetic anisotropy [1][2][3][4]. It was found that the peak arises when the external magnetic field H 0 is in the film plane and directed perpendicularly to the easy anisotropy axis n u , whereas its magnitude is equal to the anisotropy field H u =2K u /M 0 (here K u is the first-order term in the uniaxial anisotropy energy and M 0 is the saturated magnetization).…”

“…range up to ∼10 8 -10 9 Hz. As follows from the theory based on the Landau-Lifshits equation [5], the FMR frequency f 0 becomes zero in the specific point [1][2][3][4], so the FMR is changed to the low-frequency relaxation absorption. For this reason, we will use the term 'ferromagnetic pseudoresonance' introduced in [4].…”

“…It is seen that the singularities ω 0 =0 are predicted at specific values H p of magnetic field which increase from H u at θ=π/2 up to H u +4πM 0 at θ=0. (The plot at θ=π/2 was used in previous studies performed with the in-plane geometry [1][2][3][4]). These singularities vanish even at minor deviation from the xz plane, see the dashed line plotted at j=2 deg.…”