Electric-Field Control of Magnetism in Complex Oxide Thin Films

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where α is the magnetoelectric tensor (in Gaussian units). On a microscopic level, the details of the mechanism leading to a linear magnetoelectric response remain to be clarified and are likely highly material-dependent. Broadly, an electric field both shifts the positions of the magnetic cations relative to the anions and modifies the electronic wave functions; both effects result in a change in the magnetic interactions, mediated primarily by the spin–orbit coupling. Three important restrictions on α are relevant in the design of new magnetoelectric materials or systems: (1) specific symmetry requirements must be met for α to be nonzero; (2) in cases where α is symmetry-allowed, there are well-defined bounds on the magnitude of its components; and (3) the material must, of course, be electrically insulating so that it is able to sustain an electric polarization. In terms of symmetry requirements, the elements of α can be nonzero only in materials that are neither time-reversalsymmetric (i.e., they are not symmetric with respect to reversal of the directions of the magnetic moments) nor spaceinversion-symmetric (i.e., they are not centrosymmetric). The linear magnetoelectric effect is described by a term in the thermodynamic potential that is linear in both the magnetic and electric fields:

of Magnetism in Complex Oxide Thin Films

Nicola A. Spaldin and R. Ramesh Abstract In this article, we review current research efforts to control the magnetic behavior of complex oxide thin films using electric fields. After providing fundamental definitions of magnetoelectric response, we survey materials, architectures, and mechanisms that exhibit promise for such electric-field control of magnetism. Finally, we mention ideas for future research and discuss prospects for the field.

Introduction The search for a general means to control the coupling between electricity and magnetism has intrigued scientists since Ørsted’s discovery of electromagnetism in the early 19th century. Traditionally, however, the study of magnetoelectric materials has been confined to academic interest, likely because of fundamental limitations on the magnitude of the magnetoelectric response. The past few years, however, have seen a tremendous revival of activity in the field of magnetoelectrics,1 motivated in large part by the entirely new device paradigms that would be enabled by electric-field control of magnetism.2,3 First, the replacement of magnetic fields— which are generated by comparatively hot, heavy, and bulky electric currents— by electric fields in existing magnetic device applications would reduce power consumption and allow for enhanced miniaturization. In addition, entirely new device paradigms could be envisaged, such as magnetoelectric storage elements, electrically tunable filter devices, and electric field manipulation of spintronics. In this article, we review recent research on the magnetoelectric effect as it pertains to oxide electronics: the electric-field control of magnetism in complex oxide thin films and heterostructur

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