Diana Estévez

Giant magnetoimpedance effect enhanced by thermoplastic drawing

We performed thermoplastic forming (TPF) on FeCoNbB metallic glass ribbons with a supercooled liquid region exceeding 100 K, and found the sample after TPF is still completely amorphous. More importantly, the giant magnetoimpedance (GMI) effect was improved after the forming process: the maximum GMI ratio and sensitivity increased from 41% to 12.3%/Oe in the case of as-cast sample to 280% and 358.2%/Oe in the case of resulting sample after TPF, respectively. The hysteresis loops and domain patterns were subsequently studied, which revealed that the primary factor leading to the improvement of the GMI effect was the enhanced longitudinal magnetic anisotropy induced by the TPF process. We therefore assume that TPF is an effective way that improves the GMI effect, which differs from conventional annealing methods.

Magnetization dynamics and ferromagnetic resonance behavior of melt spun FeBSiGe amorphous alloys

Frequency-dependent magnetic properties of melt spun Fe80B10Si10-xGex (x = 0.0–10.0) were studied by means of inductance spectroscopy (using the complex permeability formalism) and ferromagnetic resonance techniques. The magnetization dynamics showed two magnetization mechanisms, reversible bulging of domains and hysteresis. The dominant mechanism changed as Ge progressively replaced Si; the changes reflect the crystallization processes observed for higher Ge contents, x > 5. High relaxation frequencies (above 1 MHz) were observed for alloys with x ≥ 2.5. In the ferromagnetic resonance response, coupling and decoupling between the amorphous and crystalline phases were detected depending on the orientation of the alloy samples. This allowed the calculation of the anisotropy fields of the alloys—the decreasing trend with increasing Ge content was interpreted in terms of a variable easy direction.