The process of magnetization reversal in ferromagnetic Ga(1-x)Mn(x)As epilayers has been systematically investigated using the planar Hall effect (PHE). Interestingly, we have observed a pronounced asymmetry in the PHE hysteresis when the range of the field scan is restricted to fields below the final magnetization transition. The observed behavior indicates that (a) multidomain structures are formed as M undergoes a reorientation, (b) the domain landscape formed in this way remains stable even after the magnetic field is switched off, and (c) the reorientation of magnetization directions corresponding to the transition points in PHE takes place separately within each domain.
We have investigated the magnetization reorientation process of GaMnAs ferromagnetic films by changing external field direction in planar Hall effect (PHE) measurement. While the angular dependences of PHE data taken with clockwise and counterclockwise under strong magnetic field (i.e., above 400Oe) are completely overlapped without hysteresis, they are significantly different under small magnetic field (i.e., below 50Oe) by exhibiting nonabrupt hysteresis. We have analyzed such angular dependence of PHE using the magnetic free energy based on Stoner-Wohlfarth model. The behavior observed under the high field was well understood in terms of coherent rotation of magnetization in the form of single domain. However, the nonabrupt hysteric behavior observed with low field cannot be explained by a single domain picture and requires involvement of multidomain structures.
Magneto-photoluminescence (PL) is used to study carrier transfer between self-assembled quantum dots (QDs) fabricated in the form of two adjacent QD layers separated by a thin barrier, one layer consisting of CdSe QDs and one of CdMnSe QDs in a ZnSe matrix. CdMnSe is a diluted magnetic semiconductor (DMS). In contrast to typical behavior of many low-dimensional DMS systems in which the application of a magnetic field B dramatically increases the PL intensity, in double-layer structures described above we observed a striking decrease of the PL intensity as a function of B. This effect indicates carrier tunneling from the CdSe to the CdMnSe dots as the ground state in the latter is lowered via the large Zeeman shift of the CdMnSe band edges.
The distribution of magnetic domain pinning fields was determined in ferromagnetic GaMnAs films using the angular dependence of the planar Hall effect. A major difference is found between the pinning field distribution in as-grown and in annealed films: the former showing a strikingly narrower distribution than the latter. This effect, which we ascribe to differences in the degree of uniformity of magnetic anisotropy, provides a better understanding of magnetic domain landscape in GaMnAs, a subject of current intense interest.
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