Changes in the magnetic domains of hard and soft magnetic materials in bilayer setup

Abstract

Strontium ferrite (SFO, SrFe12O19) is a ferrite employed commercially for permanent magnets due to its high magnetocrystalline anisotropy, low cost, and low toxicity. However, its magnetization is moderate [1]. A possible avenue for improving such property is combining it with magnetically soft materials. It is well-known that the rigid coupling between a magnetically hard and soft material improved magnetization while avoiding a high cost in coercitivity loss. However, results have been disappointing so far as structural and geometrical limitations make it extremely challenging to fabricate. In fact, it can be found intermediate scenarios as if exchange coupling between both materials is very small, dipolar interactions might couple both layers. Thus, in order to understand the magnetic behavior in the bilayer systems we have carried out two experiments. One of them consisted on platelets of SFO with an out-of-plane magnetization direction with a Co layer deposited on top [2]. In that study, we observed no correlation between the magnetic domains of the metal and those of the SFO platelets. Therefore, in order to avoid the competition of the magnetodipolar field created by the SFO platelet with the shape anisotropy of the metal layer, we devised the second experiment using in-plane magnetized SFO films, again with a cobalt overlayer [3]. We have grown and characterized both bilayer systems using different spectroscopy, diffraction and microscopy techniques and in particular employing element-resolved magnetization maps using x-ray circular dichroism in a photoemission electron microscope.

Figure 1. Upper line: XMCD-PEEM images for a) 0º, b) 60º and c) 120º azimuthal angles obtained at the Fe L3-edge maximum (third dichroic peak). Lower line: XMCD-PEEM images for e) 0º, f) 60º and g) 120º azimuthal angles obtained at the Co L3-edge maximum. On the right side, schemes of the magnetization of the platelet d) and Co layer h) with two azimuthal angles of incoming photons are sketched.

Acknowledgement This work is supported by the Spanish Ministry of Science and Innovation and by the European Comission and by the Regional Government of Madrid. Technical support of the technical staff of CIRCE beamline of the ALBA Synchrotron Light Facility is gratefully acknowledged.

References [1] G. D. Soria et al, Sci. Rep. 9 1¿13 (2019) [2] G. D. Soria et al, Submitted [3] G. D. Soria et al, J. Phys. D: Appl. Phys. 53 344002 (2020)