Magnetic domain structure and magnetization reversal in (311)B Ga0.91Mn0.09As films

Abstract

We have used scanning Hall probe microscopy to image domain structures and magnetization reversal in optimally annealed Ga0.91Mn0.09As films grown on (311)B GaAs substrates. Unmagnetized films exhibit a disordered mazelike domain structure consistent with a composite state of regions with magnetization along [0,1,0] and [0,0,1] out-of-plane easy axes. The characteristic stripe width of ∼3μm exhibits almost no temperature dependence in the range of 5–90K, consistent with recent theoretical predictions, while the peak domain fields drop almost linearly with increasing temperature. With an applied field perpendicular to the zero-field-cooled film magnetization proceeds by the motion of rather ordered stripe-shaped domains which form preferentially along one of the [0,1,0]∕[0,0,1] easy axes. Surprisingly, stripelike domains are not clearly observed during reversal from the magnetized state, which appears to involve the propagation of magnetic “bubbles.” Weak image contrast in the magnetized state points to the existence of residual magnetic disorder in the films on an ∼2–3μm length scale. Abrupt breaks within single images indicate the occurrence of large Barkhausen events when domain walls suddenly jump over ∼1μm distances. This implies the existence of strong pinning sites on this length scale and this, as well as the residual magnetic disorder, may be related to microscopic Mn-rich regions formed during sample growth.

Scanning Hall probe microscopy of a diluted magnetic semiconductor

“…We believe that the features seen in these images are due to clusters of MnAs ͑pure Mn is antiferromagnetic͒. Similar defects have been observed by Pross et al 31,32 Bulk MnAs has a T C of 318 K, so it should be measurable in the SQUID magnetometer, yet Fig. 6͑b͒ indicates that the MnAs clusters make a negligible contribution to the bulk magnetic moment above ϳ95 K. This illustrates the point that SHPM can detect traces of magnetic inhomogeneities that are difficult to detect with a bulk measurement.…”

Magnetic anisotropy of epitaxial (Ga,Mn)As on(113)AGaAs

“…Until now, magnetic anisotropy in such films was probed at low temperatures by magnetoresistance, [19][20][21][22] scanning Hall probe microscopy, 23 and ferromagnetic resonance measurements. 21,24,25 Experimental techniques employed here include superconducting quantum interference device ͑SQUID͒ magnetometry, ferromagnetic resonance ͑FMR͒, and polar magnetooptical Kerr effect.…”

Quantitative modeling of the annealing-induced changes of the magnetotransport in Ga1−xMnxAs alloys

“…The ferromagnetic domain size is reported to be in the micrometer range, depending on the annealing conditions between 2 and 100 m. [45][46][47] Regions which exhibit ferromagnetism above T C are also reported. The microscopic origin of these ferromagnetic islands is still not fully understood.…”