Ferromagnetic Resonance in Multidomain Thin Films

Abstract

A thin Ni-Fe film, having a uniaxial magnetic energy of the form EK = K sin2θ, usually exists as a single domain. If a magnetic field of sufficient magnitude is placed perpendicular to the easy axis of magnetization and then removed, the film splits into a large number of 180° domains. When this simple multidomain structure occurs, it is theoretically possible to excite two ferromagnetic resonance modes by applying a small magnetic field perpendicular to the easy axis. The first of these, a low-frequency mode (0–10 Mc/sec) is excited by an rf field perpendicular to the domain walls; and the second, a high-frequency mode (0–25 Gc/sec) is excited by an rf field parallel to the domain walls. The high-frequency mode has been observed in a number of films having anisotropy fields from 3–5 Oe. The experimental results are compared with theoretical relations for frequency as a function of applied field. In addition, it is possible to estimate the domain wall separation from measurements of the high-frequency mode. These measurements indicate that typical domain widths range from 30 to 50 μ. A difference is observed in the position of the absorption peak when measured in an increasing field than when measured in a decreasing field. This hysteresis is explained by the Bloch-Néel wall transition theory which was used to explain the constricted M-H loops. Attempts to observe the low-frequency mode were not successful.

Hysteretic giant magnetoimpedance effect analyzed by first-order reversal curves

“…Following ref. [17], its physical signification is explained in terms of the transitions between Bloch and Néel domain walls. The novel established FORC procedure for GMI signal (called GMI-FORC) allows the investigation of the effects of different parameters (current amplitude and frequency, ribbon characteristics, etc.)…”

Low-field microwave absorption in epitaxial La0.7Sr0.3MnO3films

“…where d is the film thickness and w is the domain width [18], Eq.13 yields ω h ≈ γM x √ wd w+d (we neglected here the contribution of stress and crystallographic anisotropy to N z ). When the field is decreased to zero the magnetization in domains rotate (affecting M x ), domain width w also changes, in such a way that ω h and, correspondingly, the microwave susceptibility (Eq.12) can pass through the resonance.…”

“…The few studies of films with in-plane magnetization were restricted to the case of uniaxial anisotropy and parallel field orientation [18,19]. Here, we consider a ferromagnetic film with biaxial easyplane anisotropy in oblique field and calculate its highfrequency susceptibility following the approach of Refs.…”

“…Here, we consider a ferromagnetic film with biaxial easyplane anisotropy in oblique field and calculate its highfrequency susceptibility following the approach of Refs. [18][19][20].…”

“…The dominant contribution at radiofrequencies arises from magnetoimpedance [6][7][8] (the field dependence of the skindepth) and domain wall resonances [9][10][11], while at microwave frequencies it is commonly attributed to various ferromagnetic resonances in the magnetically unsaturated state. These include non-aligned FMR mode [12,13], the natural FMR [14], off-resonant absorption associated with the FMR tail [15,16], and the domain mode resonances [17][18][19][20][21][22][23][24][25]. Magnetoresistive absorption in conducting ferromagnetics contributes at all frequencies and is most spectacular at the field when magnetization changes abruptly, namely at zero field [26,27] and upon transition from the unsaturated to saturated state [28][29][30][31][32].…”