Thickness-dependent resonance frequency of non-uniform procession mode in CoZr stripe-domain magnetic films

Abstract

The magnetic properties of CoZr magnetic thin films with stripe domains are investigated. The nanocrystalline grain size of 21.2 nm of CoZr thin film was obtained by x-ray diffraction spectra. The rotatable stripe-domain structure of the samples can be clearly observed from the magnetic force microscopy images. From the results of the M-H loop, the typical loops with domain structure of the samples can also be seen. The saturation magnetic fields of the thin films increase as a function of stripe half period in static magnetic properties. In dynamic magnetic properties, we find two precession modes, which include one traditional uniform precession mode with the resonance peak position in the low-frequency band and the other as the non-uniform precession mode with the resonance peak position in the high-frequency band. The ferromagnetic resonance frequencies of the non-uniform procession mode, which are driven by the exchange coupling between adjacent domains, show a decrease in behavior from 5.11to 3.52 GHz in the zero-field dynamic permeability spectra with the stripe domain's half period increasing, while the ferromagnetic resonance frequencies of the uniform procession mode nearly remain constant. Similar behavior of exchange coupling can be found by analyzing the field-dependent dynamic permeability spectra of CoZr films, which indicates that the main contribution of the thickness-dependent resonance frequency is the exchange coupling between neighboring stripe domains.

Angular control of multi-mode resonance frequencies in obliquely deposited CoZr thin films with rotatable stripe domains*

“…where f non−uni is the resonance frequency of non-uniform precession mode, and H ex is the effective field caused by the interdomain exchange coupling. This behavior has been verified in our paper, [34] in which the f non−uni can be adjusted by tuning the strength of inter-domain exchange coupling dependent on the domain width.…”

“…The non-uniform precession mode is generated by the exchange interaction induced by the precessions of unparallel magnetic moments. [31,33,34,36] For the films deposited at higher oblique deposition angles, the resonance peaks are too weak to be clearly detected. According to the Acher's limit, (µ s −1) f 2 r = [(γ/2π)4πM S ] 2 , [46,47] it can be un-derstood that the permeability becomes smaller when the resonance frequency turns larger.…”

“…Many researches including our recent research revealed that the similar out-of-phase resonance mode also exists in the film with stripe domain structure. [31][32][33][34] In the films with stripe domains, the magnetic moments in neighboring domains or domain walls are not completely parallel or antiparallel. [35,36] Therefore, the high-frequency resonance mode related to the out-of-phase precession in the film with stripe domain structure is called the non-uniform precession mode instead of the optical resonance mode.…”

“…[35,36] Therefore, the high-frequency resonance mode related to the out-of-phase precession in the film with stripe domain structure is called the non-uniform precession mode instead of the optical resonance mode. [31,36,37] By employing the Landau Lifshitz's equation, [38] the Kittel's formula of the non-uniform precession mode under zero field can be replaced by [30,34,39,40]…”

“…In this paper, CoZr thin films, each with a large saturation magnetization and a small magneto-crystalline anisotropy, are chosen to form stripe domain structures and construct rotatable anisotropic systems. [34] Combining the non-uniform precession mode with the rotatable anisotropy, the multi-mode resonance is achieved in the obliquely deposited CoZr thin film with rotatable stripe domains. Furthermore, the angular control range of multi-mode resonance frequency can be adjusted more flexibly by changing the oblique deposition angle.…”