Oscillatory Exchange Coupling and Giant Positive Magnetoresistance inTiN/Fe3O4Superlattices

Abstract

Oscillatory exchange coupling is observed in TiN͞Fe 3 O 4 superlattices over length scales comparable to metallic superlattices. However, the strength of the coupling is almost an order of magnitude stronger than that commonly observed in metallic superlattices. In addition, a unique positive magnetoresistance effect is also seen. These observations are discussed in terms of the carrier confinement effects caused by the half metallicity of the magnetic layers. PACS numbers: 75.70.Cn, 75.30.Et The exchange coupling between two magnetic layers separated by a thin nonmagnetic layer is seen to oscillate as a function of the thickness of nonmagnetic layer and the oscillation amplitude is seen to damp with increasing thickness [1]. Initial attempts to explain this phenomenon using free electron RKKY-type models predicted periods of oscillation ഠp͞k F , much shorter than the commonly observed periods (ഠ10 Å) [2]. Subsequent work brought out the fact that the discrete nature of the variable spacer thickness leads to long periods due to aliasing. It is now accepted that the oscillation periods are determined by the extremal Fermi surface spanning vectors (connecting critical points on the spacer layer Fermi surface), while the properties of magnetic layers mainly influence the amplitudes and phases of the oscillations [3]. Recently, Bruno [4] and Stiles [5] have shown that the coupling can be described in terms of the quantum interference due to spin dependent reflections of Bloch waves at the interfaces. The interest in this subject continues to grow as evidenced by several recent papers [6-13], which cover interesting issues such as the effect of cap layer, ordering in alloy layers, quantum oscillations of spin density, etc.Interestingly, the entire research on oscillatory coupling is thus far concentrated only upon pure metals or metal alloys. As is well known, oxides display a very broad range of electrical properties from insulating to superconducting. The magnetic phenomena in oxides also have several facets, with the underlying mechanisms covering direct exchange, superexchange, and double exchange. There is also a wide variety of half metallic oxides such as the manganites, magnetites, molybdates, rhenites, etc., where 100% spin polarization is seen at Fermi level. In spite of such richness of available property space, it is surprising that hardly any studies have yet been reported on oscillatory exchange coupling in heterostructures based on oxides or other compounds. One possible cause for this may be the difficulties encountered in realizing perfect interfaces of defect-free ultrathin films of dissimilar systems of oxides or other compounds. Indeed, all previous attempts at observing oscillatory coupling in compounds have failed [14,15]. In this work, we demonstrate for the first time that oscillatory exchange coupling effects can be realized in magnetic oxide based heterostructures, provided superlattices (SL) with high quality interfaces can be grown. We also observe an entirely unique giant positive magne...

Interfacial strain measurements ofSrRuO3∕SrMnO3magnetic multilayers

“…Magnetic multilayer structures based on transition metals 1,2 and their compounds [1][2][3][4][5][6][7][8][9][10][11][12][13][14] have high potential for technological applications as their transport and magnetic properties can be controlled with the non-magnetic spacer layer thickness. However, to use these materials for applications, it is necessary to understand and control precisely the physical properties that depend on various parameters such as the layer materials, their thicknesses and the interfaces between them.…”

Effect of electric/magnetic field on pinned/biased moments at the interfaces of magnetic superlattices

“…The magnetic structure based on 3d -transition metal compounds exhibit overdamped oscillatory exchange coupling [1,2,3], unidirectional magnetic anisotropy such as horizontal/vertical magnetic hysteresis loop shifts [4,5,6,7] and enhanced coercivity [8,9]. In antiferromagnetic(AFM)/ferromagnetic(FM) heterostructures the coercivity and unidirectional anisotropy are enhanced, in contrast to corresponding free magnetic multilayers.…”

Superconducting and normal-state interlayer exchange coupling inLa0.67Sr0.33MnO3−YSenapati1, Budhani2 2005Phys. Rev. B360350View full textAdd to dashboardCite

“…The oscillatory nature of exchange coupling between two ferromagnetic (FM) layers separated by a metallic but non-magnetic (NM) spacer as a function of the spacer thickness d n is now well established in a variety of systems 1,2,3,4,5,6,7 . It is generally agreed that the coupling is driven by the Rudderman-Kittel-Kasuya-Yoshida (RKKY)-type exchange through the conduction electrons of the spacer 1 .…”