Ferromagnetic resonance (FMR) in a single thin conducting ferromagnetic wire is investigated from theoretical and experimental points of view. It is shown that the wire radius, the symmetry of microwave magnetic field at the sample surface, and the skin depth (magnetic and nonmagnetic) should be considered as a whole for a correct interpretation of the microwave absorption. As a consequence, various resonance modes can be excited in metallic wires. The resonance fields of bulk samples satisfy the Kittel's resonance condition for a thin planar plate (FMR 0). However, as the wire radius decreases below the nonmagnetic skin depth a weak resonance peak separates from the main resonance and moves to the field fulfilling the Kittel's resonance condition for an axially magnetized cylinder (FMR 1). Theoretical predictions show that this "insulator" resonance mode should be the dominant one for a nanowire, where the radius is much smaller than the minimum magnetic skin depth. The existence of the two resonance modes is supported by experimental results on thin (down to 1.5-μm thick) amorphous microwires.
A single domain wall (DW) moves at linearly increasing velocity under an increasing homogeneous drive magnetic field. Present experiments show that the DW is braked and finally trapped at a given position when an additional antiparallel local magnetic field is applied. That position and its velocity are further controlled by suitable tuning of the local field. In turn, the parallel local field of small amplitude does not significantly affect the effective wall speed at long distance, although it generates tail-to-tail and head-to-head pairs of walls moving along opposite directions when that field is strong enough.
The local magnetization profile along the length in magnetostrictive Fe-based magnetic microwires has been determined by magneto-optical Kerr effect. The study has been performed in microwires with different geometrical dimensions (i.e., diameter and length). The profiles of remanent magnetization and coercivity remain constant at the middle part for all microwires, whereas significant reduction of net magnetization accompanied by significant change of coercivity is observed when approaching their ends. This local region extends just few tens of micrometer for thin (around 1 μm diameter) wires and up to several hundreds of micrometer for thick (around 10 μm diameter) wires. That predicts that critical length to observe bistability goes from 50 μm to nearly 1 mm as diameter increases from 1 to 10 μm. Results are further interpreted considering the local distribution of magnetic charges at the ends which, arising to reduce stray fields, lead in some cases to inverted loops.
The damping mechanisms affecting the motion of a single domain wall were studied in a thin bistable magnetic wire. It was found that the overall damping is frequency and temperature dependent through the locally induced anisotropy via structural relaxation. This phenomenon can increase the overall damping by one order of magnitude and enables an effective tailoring of the domain wall dynamics according to required application.
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