Training-Induced Positive Exchange Bias inNiFe/IrMnBilayers

Abstract

Positive exchange bias has been observed in the Ni81Fe19/Ir20Mn80 bilayer system via soft-x-ray resonant magnetic scattering. After field cooling of the system through the blocking temperature of the antiferromagnet, an initial conventional negative exchange bias is removed after training, i.e., successive magnetization reversals, resulting in a positive exchange bias for a temperature range down to 30 K below the blocking temperature (450 K). This new manifestation of magnetic training is discussed in terms of metastable magnetic disorder at the magnetically frustrated interface during magnetization reversal.

Antiparallel interface coupling evidenced by negative rotatable anisotropy in IrMn/NiFe bilayers

“…It has also been claimed that at IrMn/CoFeB interfaces uncompensated Mn spins can couple antiferromagnetically to the FM spins resulting in PEB. 7,42 Our data are consistent with a scenario where parallel and antiparallel couplings between the FM and UCSs coexist 6 due to, e.g., the multiple chemical elements present in this region. Two possible interface bonding types are Fe-Mn and Ni-Mn.…”

“…It is worth noting that a model which takes into account such field-induced spin-flip transitions of the interfacial spins 16 has been able to reproduce the PEB induced by athermal training 6 as well as the recovery of training after application of strong magnetic fields. 44 …”

“…The conjecture of antiparallel coupling at the IrMn/NiFe interface agrees with works on the same system. 6,39 Experiments 40 and calculations 41 have established the antiparallel Fe-Mn configuration for small surface coverage of Mn atoms. It has also been claimed that at IrMn/CoFeB interfaces uncompensated Mn spins can couple antiferromagnetically to the FM spins resulting in PEB.…”

Exchange bias effect in alloys and compounds

“…As seen in figure 2 and right inset of figure 3, the values (filled symbols) as obtained from the fit using equation (2) can satisfactorily match with all the experimental data. Recently, the exponential dependence of training effect with λ has been demonstrated in a NiFe/IrMn bilayer [122] and Pt/Co/Pt/IrMn multilayers films [123]. This training effect was interpreted in terms of metastable magnetic disorder at the magnetically frustrated interface during magnetization reversal process.…”

Determination of the Fe magnetic anisotropies and the CoO frozen spins in epitaxial CoO/Fe/Ag(001)

“…These models were soon replaced by more sophisticate models which are believed to better represent realistic experimental systems [8,9,10]. In experiment, most of the early measurements are on the FM layer hysteresis loops to study the pinning effect [11,12,13], training effect [14,15,16], and the finite size effect [17,18], etc. One important issue in these studies is on how the AFM/FM interfacial coupling determines the FM layer exchange bias and the magnetic anisotropies.…”