Epitaxial exchange-bias systems: From fundamentals to future spin-orbitronics

Abstract

Exchange bias has been investigated for more than half a century and several insightful reviews, published around the year 2000, have already summarized many key experimental and theoretical aspects related to this phenomenon. Since then, due to developments in thin-film fabrication and sophisticated characterization methods, exchange bias continues to show substantial advances; in particular, recent studies on epitaxial systems, which is the focus of this review, allow many long-standing mysteries of exchange bias to be unambiguously resolved. The advantage of epitaxial samples lies in the well-defined interface structures, larger coherence lengths, and competing magnetic anisotropies, which are often negligible in polycrystalline samples. Beginning with a discussion of the microscopic spin properties at the ferromagnetic/antiferromagnetic interface, we correlate the details of spin lattices with phenomenological anisotropies, and finally connect the two by introducing realistic measurement approaches and models.We conclude by providing a brief perspective on the future of exchange bias and related studies in the context of the rapidly evolving interest in antiferromagnetic spintronics.

Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons

“…Experimental feasibility. -The fabrication of proposed bilayers with uncompensated and low disorder interfaces, albeit challenging, is within the reach of contemporary state-of-the-art techniques [23,36]. The choice of materials is likely to be dictated by the growth, rather than theoretical, considerations.…”

Subterahertz spin pumping from an insulating antiferromagnet

“…These qualities have pushed antiferromagnets into the limelight as suitable candidates for faster, compact, and more efficient materials for spintronic applications [3]. Antiferromagnets have been considered suitable only for theoretical considerations as put forth by Louis Néel in this Nobel lecture from 1970 [5], until the early 1990s when exchange bias found its place in large scale industrial application in recording heads of memory devices (hard disks, Figure (1.1)) [6][7][8]. Indeed, antiferromagnets have been used commercially to provide exchange bias to pin down the magnetization of reference ferromagnetic layer in spin valves.…”

Maximizing Exchange Bias in Co/CoO Core/Shell Nanoparticles by Lattice Matching between the Shell and the Embedding Matrix

“…Exchange bias refers to a set of different phenomena (e.g., loop shifts in the field axis, HE, coercivity enhancement or loop asymmetries, among others) which arise when two materials with significantly different magnetic anisotropy, typically a ferromagnet (FM) and an antiferromagnet (AFM), are exchanged coupled at their mutual interface. [1][2][3][4][5] Although most devices exploiting exchange bias effects rely on thin films, [6][7][8] new applications based on nanoparticles, such as coercivity enhancement for permanent magnets 9,10 , microwave absorbers 11 or novel spintronic devices, 12,13 are continuously emerging. Driven by the existing and prospective applications, there is currently a trend to try to enhance the different exchange bias-related effects.…”