Local coercivity at X-ray nanobeam irradiated regions in amorphous Fe80B20 stripes

U Urdiroz,F J Palomares,G Martínez Criado,F Cebollada,J M González,E Navarro,M Sánchez-Agudo

doi:10.1063/9.0000090

Abstract

We report on the effect, on the local magnetization reversal taking place in amorphous Fe80B20 stripes, of the irradiation with nanobeam synchrotron X-ray. That irradiation preserves the amorphous structure and results on the increase of the local coercivity with respect to that measured in a non-irradiated sample, in which the coercivity is mediated by the nucleation-propagation of a single wall. The local coercivity increases in a non-linear way with the width of the irradiated regions when that width is smaller than that of the wall mediating the magnetization switching in the non-irradiated stripe and gets saturated when the irradiated regions dimension is larger than the propagating wall width. We correlate this behavior with the induction at the irradiated regions of a reduction of the local effective anisotropy with respect to the stripe as-lithographed value. From the relationship between the coercivity and the width of the irradiated regions we estimate the local anisotropy reduction in a 25% of that measured in the non-irradiated stripe.

Highlights

We report on the effect, on the local magnetization reversal taking place in amorphous Fe80B20 stripes, of the irradiation with nanobeam synchrotron X-ray
The local coercivity increases in a non-linear way with the width of the irradiated regions when that width is smaller than that of the wall mediating the magnetization switching in the non-irradiated stripe and gets saturated when the irradiated regions dimension is larger than the propagating wall width
The as-lithographed stripes exhibited shape anisotropy with easy axis (e.a.) along the stripe long axis and a square hysteresis loop was measured along that direction, see Figure 1

Summary

Introduction

Ferromagnetic metallic amorphous systems are characterized by the possibility of modifying their effective anisotropy1 due to their metastable nature that favors the occurrence of atomic diffusion.2 Thermal treatments carried out at temperatures significantly below the crystallization onset result on a reduction of the as-prepared material built-in anisotropy, which can be associated to structural relaxation/free volume elimination and/or stresses relief.3 When the treatments are performed at temperatures closer to the crystallization onset, while keeping the samples submitted to diffusion polarizing magnetic and/or stress fields, it is possible to induce controlled easy axis direction anisotropies with constants of the order of 1-5 x 104 erg/cm3.4–6 In the particular case of the amorphous magnetic films, the induction of anisotropy at the local scale has been implemented by using a variety of techniques including ion implantation,7–10 electromagnetic irradiation,11 coupling to locally strained regions,12 and local anneals carried out by means of current circulating through auxiliary conducting tracks.13 In a previous paper14 the authors have shown how irradiating with synchrotron X-ray (2 μm sized beam) the same amorphous Fe80B20 stripes studied here results on anisotropy modifications over regions spanning ca. 15 μm.In the present work we explore the local anisotropy changes induced in amorphous Fe80B20 stripes by means of nanosized X-ray beams since that length scale is of special interest from the standpoint of the implementation of spin waves-based devices and circuitry of the types proposed to implement processing components (i.e.: logic gates14,15).SAMPLES AND EXPERIMENTAL. That irradiation preserves the amorphous structure and results on the increase of the local coercivity with respect to that measured in a non-irradiated sample, in which the coercivity is mediated by the nucleation-propagation of a single wall.

Results

Conclusion