Co layer thickness dependence of exchange biasing for IrMn/Co and FeMn/Co

Abstract

We present a high resolution study of the ferromagnetic layer thickness dependence of exchange bias field (H EB) and coercivity (H C) in IrMn/Co and FeMn/Co bilayers using the magneto-optical Kerr effect. Samples are sputtered wedges on silicon with Co thicknesses ranging from 1 to 17 nm. The IrMn/Co ͑with exchange bias interface energy of ϳ0.14 erg/cm 2 ͒ shows square loops, a smooth increase in H EB with inverse thickness, and a complicated behavior for coercivity, perhaps due to competition with thickness dependent coercive mechanisms. The FeMn/Co ͑with exchange bias interface energy of ϳ0.059 erg/cm 2 ͒ shows more rounded loops, a plateau of H EB with decreasing thickness, and a smooth increase in coercivity with inverse thickness.

A new paradigm for exchange bias in polycrystalline thin films

“…14. Due to the F layer thickness dependence of exchange bias, such a system gives rise to two hysteresis loops shifted by differing amounts [58]. The initial hysteresis loop for the system is shown in Fig.…”

Scaling behavior of the exchange-bias training effect

“…Deposition takes place under ultrahigh vacuum ͑UHV͒ condition at a base pressure of 5.0ϫ 10 −11 mbar and a substrate temperature of 573 K. An average thickness gradient of 3 to 28 nm over 1 cm lateral distance was achieved by partially opening the shutter of the effusion cell and projecting the truncated beam profile onto the substrate. Unlike other step wedges where sample growth was controlled by using shutter motion attached to the substrate, 32,33,41 we exploit shutter control of the Co effusion cell allowing for the growth of a continuous Co wedge. Figure 1 shows the local Co thickness probed along the direction of the thickness gradient at individual positions x of the wedge.…”

“…27,28,[32][33][34] The inverse FM thickness dependence reveals the interface nature of the EB effect and reflects the origin of EB as a competition between the Zeeman energy of the FM layer and AF/FM interface coupling energy. It is the detailed microscopic understanding of the latter which is still under debate.…”

Giant parallel and perpendicular exchange biases in MnPd/Co bilayers

“…These J K are several orders of magnitude larger than those observed on most of the metallic exchanged bias thin films [2]. For example, in MnPd/Fe bilayers, the J K value is only 0.032 erg/cm 2 [13] and 0.017 erg/cm 2 [14], in MnIr/Co bilayers, the J K value is 0.14 erg/cm 2 [15] and MnFe/Co bilayers, the J K value is 0.059 erg/cm 2 [15]. In the literature, there are few systems, which exhibit such large unidirectional anisotropy constant.…”