Effect of the nonmagnetic layer in a Co/Cu/CoO trilayer structure on the exchange coupling in it
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Effect of the Nonmagnetic Layer in a Co/Cu/CoO Trilayer Structure on the Exchange Coupling in It P. D. Kima,*, S. C. Yub, G. S. Patrina,c, Yu. Y. Songb, I. A. Turpanova, D. L. Khalyapina,c, and D. A. Marushchenkoa,c,** a
Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia *email: [email protected] b BK21 Physics Program and Department of Physics, Chungbuk National University 361763, Cheongju, South Korea c Siberian Federal University, Krasnoyarsk, 660041 Russia **email: [email protected] Received March 11, 2010
Abstract—The dependence of the exchange bias of epitaxial singlecrystal Co/Cu/CoO trilayer films on the copper layer thickness and temperature is studied. The exchange bias of the hysteresis loops of the ferromag netic cobalt layer as a function of the copper layer thickness is found to have a wellpronounced oscillating character. The oscillations manifest themselves over the entire temperature range in which an exchange bias takes place (77–220 K). The complex variation of the oscillation amplitude with the nonmagnetic layer thick ness can be explained by the superposition of two interlayer exchange coupling oscillation periods (λ1 ≈ 10– 11 Å, λ2 ≈ 20 Å) having different amplitudes and temperature dependences. DOI: 10.1134/S1063776111030058
INTRODUCTION The phenomenon of the unidirectional anisotropy induced by the exchange coupling at the interface between two materials with different types of magnetic ordering, namely, ferromagnetic (F) and antiferro magnetic (AF) materials, has attracted the attention of researchers from a standpoint of both the fundamental problems of coupling in heterogeneous systems and possible practical applications. Although this phe nomenon has long been studied [1], there is no gener ally accepted concept of the nature of this phenome non. For example, there is no agreement among researchers regarding the type of this coupling, i.e., shortrange [2] or longrange [3] coupling. The assumptions that a unidirectional anisotropy results from the exchange coupling between the neighboring spins of F and AF materials at the interface point to the possibility of such coupling in the case of F and AF materials separated by a conducting layer of a non magnetic (NM) material, as in the case of F/NM/F structures. Indeed, the longrange exchange coupling through the conduction electrons of a nonmagnetic layer between F layers in magnetic multilayer struc tures (F/NM)n and related structures has been much
studied [4–6]. This coupling has an oscillating charac ter as a function of the NM layer thickness and is well explained by the theories based on an indirect exchange (RKKY coupling) model [7, 8]. On the other hand, the coupling between F and AF layers is much more complex: the exchange bias field was found to strongly depend on a spin structure at the interface. The interface roughness, the presence of domain walls, and the relative orientation of the spins of F and AF l
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