Exchange bias in epitaxial Fe/Ir_0.2Mn_0.8bilayers grown on MgO (0 0 1)

Abstract

Exchange bias has been studied in epitaxial Fe/Ir0.2Mn0.8 (IrMn) bilayers grown by molecular beam epitaxy on MgO (0 0 1) substrates. The IrMn layer has a chemically disordered fcc structure with an epitaxial relationship of MgO(0 0 1)[1 1 0]//Fe(0 0 1)[1 0 0]//IrMn(0 0 1) [1 1 0]. In this system, exchange bias is induced during growth at room temperature without post-annealing, by applying a small magnetic field, HA, along the bcc Fe [1 0 0] easy axis. The temperature dependence of the exchange bias field and the coercivity along the Fe [1 0 0] easy axis, measured up to approximately half the Néel temperature, shows an exponential decay of these parameters with increasing temperature. The magnetization measured as a function of applied field along the Fe [1 0 0] easy axis results in a negatively shifted hysteresis loop, typical for exchange bias, while when the magnetic field is applied along the Fe [0 1 0] easy axis (perpendicular to HA), a symmetric double-shifted loop is observed. In both cases, the magnetization reversal occurs through two successive events involving nucleation and propagation of domains in which the magnetic moments are perpendicular to each other. We demonstrate that due to the epitaxial growth of the IrMn layer, the unidirectional anisotropy induced by exchange bias is aligned with one of the Fe easy axis directions and, in effect, is added to the four-fold cubic anisotropy of the Fe layer.

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

“…Theoretically, both the coherent rotation and the DW nucleation can result in irreversible Barkhausen jumps, the two reversal mechanisms as well as the asymmetrical one have been observed in various EB systems 17,18,26,27 . We have tried to use the coherent rotation to explain the hysteresis loops for a-axis oriented MnPd/Fe EB bilayers, but the prediction for the coercivity is obviously too large 28 .…”

“…We have tried to use the coherent rotation to explain the hysteresis loops for a-axis oriented MnPd/Fe EB bilayers, but the prediction for the coercivity is obviously too large 28 . On the other hand, by using Lorentz transmission electron microscopy, Wang et al directly observed that the magnetization reversal in epitaxial IrMn/Fe bilayers occurs through DW nucleation and propagation 26 . Inspired by these works, we tentatively extend the DW nucleation model developed for Fe/MgO(001) films to account for the magnetization reversal in epitaxial MnPd/Fe EB bilayers.…”

Structural characterization of interfaces in epitaxial Fe/MgO/Fe magnetic tunnel junctions by transmission electron microscopy

“…12,22,23 Various in situ techniques including surface x-ray diffraction 24 and x-ray magnetic circular dichroism 25,26 have been used to characterize the Fe/MgO interface structure, arriving at conflicting conclusions. Serin et al 18 measured an asymmetry in the roughness of the two interfaces, using STEM to collect electron energy-loss spectroscopy ͑EELS͒ data.…”

Spin-dependent tunneling spectroscopy for interface characterization of epitaxial Fe/MgO/Fe magnetic tunnel junctions

“…Detailed descriptions of the growth process, the structural characterization, and junction fabrication can be found elsewhere. [22][23][24] The magnetotransport properties were measured in a physical properties measurement system using a standard fourprobe technique. Dynamic conductance ͑dI / dV − V͒ and IET spectrum ͑d 2 I / dV 2 − V͒ were measured at 30.79 Hz with an ac modulation voltage of 4 mV using a standard lock-in method.…”