Thickness dependence of exchange bias and structure in MnPt and MnNi spin valves

Abstract

We describe x-ray diffraction and magnetic measurements of annealed MnPt and NiMn spin valves as a function of MnPt (NiMn) film thickness. Thin films (≲5–10 nm) are not chemically ordered and hence not antiferromagnetic, which explains the lack of exchange coupling in these films. With increasing thickness, the L10 chemical order develops (through coexistence between fcc and L10 phases) and there is a strong correlation between chemical order and exchange coupling. The lack of chemical order in the thin films is likely due to a lack of nucleation sites for the L10 phase.

Enhancement of exchange bias in thin PtMn antiferromagnets by Ru and Cr nano-lamination

“…The possible reasons are as follows: first, the FCT phase transformation of PtMn is incomplete. Toney et al [7] have investigated AF phase transformation for PtMn and NiMn spin valve by XRD. They showed the coexistence of FCC and FCT phases in PtMn from 5 to 25 nm.…”

“…This insertion layer breaks the AF film growth at an early stage. With such a thin AF (X3), which is much less than the critical thickness [1,2,7], the AF film is dominated by the chemically disordered FCC phase. It contributes to the FCT phase growth when the AF thickness increases.…”

Structural characterization of MnNi and MnPt antiferromagnetic materials for spintronic applications

“…These materials currently include MnPt [6][7][8][9] and MnNi [10][11][12]. The existence of the AFM phase in both these materials is known to be linked to the corresponding microstructure.…”

Epitaxial PtMn∕NiFe exchange-biased bilayers containing directly deposited ordered PtMn

“…Despite the high stability of the magnetic properties, it is still necessary to discuss the inferior exchange biasing as compared to the polycrystalline postgrowth-annealed exchange-biased systems with ͑111͒ texture. 11,12 The magnetic moments of the Mn atoms are antiferromagnetically aligned along the c axis, which means that for our samples the magnetic moments in the PtMn layer are aligned perpendicular to the interface, with a compensated spin configuration. Although there may be an induced in-plane magnetization component in the PtMn layers in the vicinity of interface because of spin canting 13 or defects such as interfacial roughness 14 or grain boundaries, it is insufficient for exchange coupling with the NiFe magnetization across the interface, which can explain the low exchange-bias field.…”