Antiferromagnetic layer thickness dependence of the magnetization reversal in the epitaxial MnPd/Fe exchange bias system

Abstract

We report an investigation on the antiferromagnetic layer thickness dependence of magnetization reversal in c-axis oriented MnPd/Fe epitaxial exchange biased bilayers. Several kinds of multi-step loops were observed for different samples measured at various field orientation. The evolution of the angular dependent magnetic behavior evolving from a representative Fe film to the exchange biased bilayers was revealed. With increase of the thickness of the antiferromagnetic layers, asymmetrically shaped loops and biased two-step loops are induced by exchange bias. Including the unidirectional anisotropy, a model based on the domain nucleation and propagation was developed, which can nicely describe the evolution of the magnetic behaviors for MnPd/Fe bilayers and correctly predicts the critical angles separating the occurrence of different magnetic switching processes. For fields applied along the bias direction, the 180 o magnetic reversal changes from two successive 90 o domain wall nucleations to a single 180 o domain wall nucleation at a critical thickness of the MnPd layer.

Magnetization reversal in epitaxial exchange-biased IrMn/FeGa bilayers with anisotropy geometries controlled by oblique deposition

“…The previously studied epitaxial systems usually possess comparable K eb and K u . Changing the EB will lead to a corresponding variation of K u [15,21]. In an experiment, a large ratio of K u /K eb can be well defined by obliquely depositing a FM layer to achieve a large K u while reducing the AFM thickness to obtain a small K eb , which could significantly change the magnetic switching.…”

“…In contrast, the 180°m agnetic switching processes in both the square and three-step loops could be well described by a model of two successive 90°DW nucleations, but not the 180°DW nucleation [23,24]. In a subsequent paper on epitaxial MnPd/Fe EB bilayers with a rather strong K eb and K u [15], the 180°magnetic switching behavior in the square loop changed to the 180°DW nucleation. In the present IrMn/FeGa EB heterostructures, the angular dependence of 90°magnetic switching fields can be easily explained by the corresponding theoretical equations based on the 90°DW nucleation [ Figs.…”

“…where ε 180 • is the 180°DW nucleation energy. The detailed derivation for these equations can be seen elsewhere [15].…”

“…Depending on the strengths and the relative orientations, the different configurations of magnetic anisotropies would give rise to complicated magnetic switching processes. For example, square, asymmetrically shaped, biased two-step, and unbiased two-step loops have been observed in c axis oriented epitaxial MnPd/Fe EB bilayers when measuring at different field orientations [15]. Conventionally, the EB-induced uniaxial anisotropy is aligned along the unidirectional anisotropy.…”

Probing magnetoelastic effects of ultrathin antiferromagnets via magnetic domain imaging in ferromagnetic-antiferromagnetic bilayers

“…film [9,[41][42][43]. Moreover, the coercivity of the FM film could be significantly enhanced because of increase of domain-wall activated processes caused by the pinning effects from the AFM layer [1,5].…”