Interlayer segregation of nonmagnetic metal spacers and its influence on exchange coupling in magnetic multilayers

Abstract

Two sets of NiFe∕FeMn films with Ta and Ta∕Cu buffer layers were prepared by magnetron sputtering to study the influence of different buffers on the exchange coupling process. The results show that the exchange bias field (Hex) of NiFe∕FeMn films with a Ta∕Cu buffer is lower than that of films with a Ta buffer. There is no apparent difference in the texture and roughness of films both with Ta and Ta∕Cu buffers. However, the segregation of Cu atoms on the surface of NiFe in the trilayer of Ta∕Cu∕NiFe was found by using angle-resolved x-ray photoelectron spectroscopy (XPS). A decrease of Hex for NiFe∕FeMn films with a Ta∕Cu buffer layer is primarily caused by the segregation of Cu atoms to the interface of the NiFe and FeMn layers. In order to suppress the Cu segregation, we deposited Bi insetting layers at the interface of Cu and NiFe in Ta∕Cu∕NiFe∕FeMn∕Ta films and found that Hex of NiFe∕FeMn can be doubled when the proper quantity of Bi is deposited. XPS analysis shows that Bi insetting layers deposited at the interface of Cu and NiFe effectively suppress the Cu segregation on the NiFe layer. As a result, Hex is increased. However, if the insetting Bi is deposited excessively, it will partially migrate to the FeMn layer, damaging the antiferromagnetic property of the FeMn layer, thereby resulting in decreased Hex. When Ag and Pb were deposited at the interface of Cu and NiFe in Ta∕Cu∕NiFe∕FeMn∕Ta films, similar experimental results were obtained.