WEB Investigating the origin of magnetic uniaxial anisotropy in cobalt ferrite induced by Spark Plasma Sintering
There is an increasing activity in improving magnetostriction of oxide-based materials and particularly in cobalt ferrites, which are suitable alternatives for rare earth-based alloys like Terfenol-D. These materials are of great importance for high performance actuators and sensors. The most common technique to tune their magnetostrictive properties is to induce a uniaxial anisotropy by magnetic-annealing .
Recently, it was shown that reactive sintering using Spark Plasma Sintering (SPS) in cobalt ferrite allowed to induce a magnetic uniaxial anisotropy in the direction of the applied pressure during the process . This feature does not appear when a simple SPS sintering is performed, which implies that the reaction step performed in SPS is responsible for the anisotropy . Hence, we are able to obtain samples exhibiting similar properties to magnetic annealed ones, but without the use of a magnetic field. In order to optimize and tune the characteristics obtained, it is then of interest to understand the origin of such magnetic anisotropy (magnetocrystalline or crystallographic texture) and establish the effects of the most important SPS process parameters (pressure or current).
In this study, we first investigate the influence of the pressure applied during SPS (10, 50 and 100 MPa). Magnetic measurements in two directions (parallel and perpendicular to the applied pressure during SPS) shows uniaxial magnetic anisotropy in all the samples. To understand the origin of such anisotropy, a heat treatment in air (400°C/1h) was done. This annealing was performed under the same conditions as for the magnetic annealing, but without magnetic field. As all the samples exhibit isotropic properties after the heat treatment, it demonstrates that the origin of the anisotropy is likely to be due to ion diffusion (like in magnetic annealing) rather than texture. Texture measurements are also performed to corroborate this results. The results of the present study will allow us to later optimize the magnetic anisotropy obtained by SPS and extend this process to other materials.
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This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the framework of the Priority Programme SPP1959.