Abstract
Ferrimagnetic alloys are extensively studied for their unique magnetic properties leading to possible applications in perpendicular magnetic recording, due to their deterministic ultrafast switching and heat assisted magnetic recording capabilities. On a prototype ferrimagnetic alloy we demonstrate fascinating properties that occur close to a critical temperature where the magnetization is vanishing, just as in an antiferromagnet. From the X-ray magnetic circular dichroism measurements, an anomalous ‘wing shape’ hysteresis loop is observed slightly above the compensation temperature. This bears the characteristics of an intrinsic exchange bias effect, referred to as atomic exchange bias. We further exploit the X-ray magnetic linear dichroism (XMLD) contrast for probing non-collinear states which allows us to discriminate between two main reversal mechanisms, namely perpendicular domain wall formation versus spin-flop transition. Ultimately, we analyze the elemental magnetic moments for the surface and the bulk parts, separately, which allows to identify in the phase diagram the temperature window where this effect takes place. Moreover, we suggests that this effect is a general phenomenon in ferrimagnetic thin films which may also contribute to the understanding of the mechanism behind the all optical switching effect.
Highlights
Ferrimagnetic alloys are extensively studied for their unique magnetic properties leading to possible applications in perpendicular magnetic recording, due to their deterministic ultrafast switching and heat assisted magnetic recording capabilities
Anomalous magnetic behaviour in form of wing shape hysteresis loop has been reported in several RE-TM ferrimagnetic alloys that exhibit a perpendicular magnetic anisotropy such as, GdCo20, HoCo21, TbFe22, GdFe23, DyCo24,25, and GdFeCo26–28 thin films
x-ray circular magnetic dichroism (XMCD) is sensitive to the ensemble averaged orbital and spin contribution to the magnetic moments projected along the circular polarization direction which is parallel to the x-ray beam direction
Summary
Ferrimagnetic alloys are extensively studied for their unique magnetic properties leading to possible applications in perpendicular magnetic recording, due to their deterministic ultrafast switching and heat assisted magnetic recording capabilities. Rare-earth-transition-metals (RE-TM) ferrimagnetic alloys have attracted great interest because they exhibit superior flexibility in designing desired properties for ultimate functionality and as model systems for basic research in the field of spintronics They can be engineered as two ferromagnetic oppositely oriented sub-lattices in form of thin films and nanostructures with controllable perpendicular anisotropy, variable net magnetization as a function of stoichiometry and tunable spin reorientation transition temperature[4]. This intriguing effect was interpreted based on models assuming an alloy composition gradient across the film thickness or even across lateral directions of the sample According to these assumptions, a magnetization compensation temperatures will occur throughout the film, possible due to local stoichiometry variations, and as a result the magnetic hysteresis loop will reflect the relative weight of the corresponding parts of the film[20,26]. We suggest that this effect may explain the origin of all optical switching in ferrimagnetic films (see Discussion section and Supplementary)
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