Observation of magnetic domain structure in a ferromagnetic semiconductor (Ga, Mn)As with a scanning Hall probe microscope

T. Shono, T. Hasegawa, T. Fukumura, F. Matsukura, H. Ohno
2000 Applied Physics Letters  
We have performed low-temperature scanning Hall probe microscopy on a ferromagnetic semiconductor ͑Ga 0.957 Mn 0.043 ͒As. The observed magnetic domain structure is a stripe-shaped pattern as has been observed in conventional nonsemiconductor ferromagnetic materials, and the measured magnetic field from the sample surface was small, reflecting the weak magnetization of ͑Ga, Mn͒As. The domain width increased and the measured magnetic field decreased with raising temperature, which are consistent
more » ... ich are consistent with calculated results, in which the exchange interaction between Mn spins deduced from the Curie temperature is assumed. Success in growth of ferromagnetic III-V-based diluted magnetic semiconductors has opened up the possibility of semiconducting devices which combine the functionality of semiconductors with that of ferromagnetic materials. 1-4 In magnetic materials, both the size and the shape of the magnetic domains are among the most fundamental quantities, because they reflect the magnitude and anisotropy of the microscopic exchange interaction. In addition, the domain structure is associated with the carrier conduction and the possible minimum size of magnetic bits in magnetic recording media, which are of technological importance for both electronic and magnetic devices. However, there have been no experiments in order to observe the magnetic domain structures of III-V ferromagnetic semiconductors. Recently, several scanning probe microscopic techniques for studying local magnetic properties, which detect the magnetic field from the sample surface, have been developed, such as the magnetic-force microscope, 5 the scanning superconducting quantum interference device microscope, 6 and the scanning Hall probe microscope ͑SHPM͒. 7 The SHPM has advantages of less magnetic invasiveness for the specimen and a wider operating temperature range, the latter being suitable for studying the temperature variation of the domain structure. Here, we report SHPM measurements of the magnetic domain structure in a ferromagnetic semiconductor ͑Ga, Mn͒As film. The results clearly showed stripe-shaped domains with their widths depending on temperature below the Curie temperature T C . The domain width and the magnitude of the magnetic field from the domain structures are discussed on the basis of a classical magnetic domain model in which magnetostatic energy and domain-wall energy are taken into account. A 0.2-m-thick ͑Ga 0.957 Mn 0.043 ͒As film was grown epitaxially on a semi-insulating GaAs͑001͒ substrate at 250°C by the use of the molecular-beam epitaxy technique. The perpendicular magnetization at zero field was realized by the introduction of tensile strain into the ͑Ga, Mn͒As layer using 1-m-thick ͑In 0.16 Ga 0.84 ͒As buffer layer. 8,9 T C is 80 K determined from a magnetization measurement. A homemade SHPM was utilized for the variable temperature measurements. 10 The Hall probe with the junction of 1 m ϫ1 m was scanned hϳ0.5 m above the sample surface in order to detect the local magnetic field perpendicular to the sample surface. Figure 1 shows the observed magnetic images of the ͑Ga, Mn͒As film at 9-77 K. The horizontal axes of the images are along ͗100͘. The color denotes the magnetic field perpendicular to the sample surface B Z . Note that each figure of Fig. 1 has a different scale of B Z , and that the scanning area for the upper and lower panels are 4.75ϫ4.75 and 7.3ϫ7.3 m 2 , respectively. The red and blue areas correspond to positive and negative B Z , respectively, hence, white boundaries with B Z ϳ0 correspond to the magnetic domain walls. The stripe direction is nearly parallel to the ͗110͘, reflecting the magnetocrystalline anisotropy, which is consistent with the theoretical prediction by the use of k• p perturbation method. 11 The stripe-shaped domain is preserved in a wide temperature range up to T C , as can be seen from Fig. 1 . The width of the domain d becomes wider, and B Z decreases with raising temperature. Figure 2 ͑square sym-bols͒ shows the temperature dependence of d. At 9 K, d is 1.5 m, then gradually increases with raising temperature for TϽ60 K, and steeply increases for TϾ60 K up to ϳ6 m around T C . a͒ Electronic
doi:10.1063/1.1290273 fatcat:te3c6iouc5hwnkwzwsfpaaoqfy