Exchange bias and asymmetric magnetization reversal in ultrathin Fe films grown on GaAs (001) substrates

Abstract

Magnetization measurements on a series of Fe films grown by molecular beam epitaxy on GaAs (001) substrates and capped with a thin Au layer reveal interesting exchange bias (EB) properties at low temperatures. The observed exchange bias decreases rapidly with increasing temperature, and completely disappears above 30 K. While the Fe samples were not grown with an intentionally deposited antiferromagnetic (AFM) layer, X-ray reflectometry, X-ray absorption near-edge spectroscopy carried out near the L-edge of Fe, and comparison with similar Fe/GaAs samples capped with Al, which do not show exchange bias, suggest that the exchange bias in the GaAs/Fe/Au multilayers is caused by an AFM Fe oxide at the Fe/Au interface formed by penetration of oxygen through the Au capping layer. The observed exchange bias is accompanied by a strikingly asymmetric magnetization reversal of the Fe films occurring when the magnetic field is applied at angles away from the easy axis of the film. The observed asymmetry can be interpreted in terms of a competition between cubic, uniaxial, and unidirectional magnetic anisotropy characteristic of the exchange-biased Fe film.

Interfacial exchange coupling in Fe/(Ga,Mn)As bilayers

“…Figure 3(a) shows normalized Fe L 2,3 XAS (I + + I − )/2 spectra recorded at 4 K for Fe(4 nm)/Ga,Mn)As(100 nm), where I + and I − indicate intensities of two counter-rotating circular polarizations of the x-ray beam. In TEY and FY modes, XAS measurements show a clear splitting in the Fe L 3 absorption peak, which is a direct signature for the formation of an Fe oxide at the Au/Fe interface, as was reported earlier [16], a result that is also directly relevant to our interpretation of the exchange bias observed at low temperatures, seen in Fig. 1.…”

“…As was shown in Ref. [16], in zero-field-cooled uniaxially anisotropic thin Fe layers exchange bias can pin two independent FM domain populations characterized by opposite exchange bias fields, as shown in Fig. 6 of Ref.…”

“…6 of Ref. [16]. Thus, in the presence of a large number of domains, one expects broad symmetric hysteresis loops resulting from the superposition of contributions from the two domain populations.…”

“…We attribute the observed exchange bias to an antiferromagnetic Fe oxide at the Fe/Au interface formed by penetration of oxygen through the Au capping layer. Evidence for the formation of Fe oxide and its effects has already been extensively discussed elsewhere [16]. The presence of the exchange bias, and the enhancement of coercive field in the Fe film associated with this effect, shed additional light on the magnetic coupling between the Fe and the (Ga,Mn)As layers, discussed below.…”

Nonresonant and Resonant Spin Rectification in the Exchange Biased NiFe/MnIr Bilayer

“…As such, it should be insightful to study the magnetization rotation in exchange biased systems via SRE since their magnetization reversal occurs in only one field direction at a non‐zero field (e.g., opposite to exchange bias field) with a large coercivity so that these magnetization reversal effects can be more easily observed without the need to switch the field polarity. In addition, magnetization reversal in exchange biased systems have been shown to be quite complicated, therefore the possible detection and characterization of magnetization rotation in such systems via spin‐sensitive SRE should be of interest.…”