Magnetically Induced Enhanced Exchange Spring Effect in CoFe₂O₄/CoFe₂/CoFe₂O₄ Films

Ezana Negusse,Conrad M Williams

doi:10.1109/tmag.2019.2961989

Abstract

Earlier, we reported exchange coupling between bilayers of CoFe 2 O 4 /CoFe 2 , where CoFe2O 4 and CoFe 2 are the hard and soft magnetic layers, respectively. These results suggested trilayers structures of CoFe 2 O 4 /CoFe 2 /CoFe 2 O 4 are strong candidates for low hysteresis loss “exchange spring materials.” To study this possibility, we extended our investigation to the synthesis of CoFe 2 O 4 /CoFe 2 /CoFe 2 O 4 trilayers under different sputtering deposition conditions, which included oxygen pressure in the case of the CoFe 2 O 4 component and the application of a magnetic field during the deposition of the soft CoFe 2 . The most significant finding was an increase in the exchange spring figure of merit (FoM) of 36% in-plane and 60% out-of-plane by the application of an applied field during the deposition of the soft CoFe 2 , resulting in a decrease in hysteretic losses by a similar percentage. We will discuss these spin spring results in terms of an increase in uniaxial anisotropy energy in the CoFe 2 layers due to short-range ordering of Fe-Fe and Co-Co pairs during deposition and an enhancement in the coercivity and remnant magnetization of CoFe 2 O 4 . We also discuss a metric (FoM) for describing enhancements due to multiple optimized deposition conditions.

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