Bulk and interfacial effects in exchange bias systems

Abstract

In this work we report on an extensive and detailed study of exchange bias systems consisting of two ferromagnetic layers deposited with an antiferromagnetic layer of IrMn between them. Systems with two different ferromagnetic layers have been studied in which sample 1 had CoFe layers of different thicknesses and sample 2 had not only ferromagnetic layers of different thicknesses but also the composition of the upper ferromagnetic layers was changed from CoFe to NiFe. In both the samples the antiferromagnetic layer thickness was maintained constant at 5 nm, NiCr seed and capping layers (5 nm) were used on all samples. Such a system is of considerable interest as the properties of each ferromagnetic layer are affected by the same antiferromagnet. However differences in behaviour will occur due to the nature of the interfaces between the different layers as well as other parameters such as the ferromagnetic layer thickness. We have conducted a study of thermal activation effects in these systems where both or a single ferromagnetic layer can be reversed whilst the system is heated. We find that we can differentiate between bulk and interface effects indicating that the role of spin disorder at the interface is crucial in determining the final value of the exchange bias.

Hysteresis Properties of Magnetic/Non-Magnetic (M/NM) Multilayers: Monte Carlo Investigation

“…Figure 5 shows that the remanent magnetization (M r ) decreases in the case of isolated clusters at the interface but the coercive field increases with interface configuration variation. A similar behavior is found experimentally and by using Monte Carlo simulations [16,17]. In fact, the magnetic moments at the core of magnetic layers turn on a uniform mode; those at the clusters of the interface turn independently, suggesting that the magnetization reversal proceeds through the mechanism of domain nucleation.…”

A new paradigm for exchange bias in polycrystalline thin films

“…We have reported on studies of trilayer systems where a single AF layer is coupled above and below to F layers of different thickness [57]. A schematic of the system studied is shown in Fig.…”

Exchange bias of patterned systems: Model and numerical simulation

“…Morales et al [8] focused on the three dimensional AF bulk structure, Dutson et al [9] and Vallejo-Outon et al [10] emphasized the importance of interface effects and AF bulk dynamics, while Roy et al [11] investigated in detail the depth profile of uncompensated spins in the AF. In a recent contribution Vallejo-Outon et al [12] presented a numerical simulation of patterned exchange bias systems consisting in an array of squares containing metallic polycrystalline AF layers.…”

“…The physical idea for the FM pinning of a fraction of the spins rests on the work by Gaunt [15], which in the EB context was already explored by O'Grady et al [9,10,16]. Gaunt's basic idea is that the ferromagnetic magnetization M(t) varies in time as…”