Abstract
We report on the applied external magnetic field, B, dependence of a magnetic domain structure and magnetization switching in MnAs nanodisks on AlGaAs nanopillar buffers selectively grown on Si (111) substrates partially covered with dielectric SiO2 thin film mask patterns by selective-area metal–organic vapor phase epitaxy. The results on the B dependence of magnetic domain structures observed by magnetic force microscopy show that the ratio, or percentage, of a single magnetic domain is minimized at B = −1.5 kG in the nanodisks with an area of 4 × 104 nm2 or smaller, although the decrease to the minimum of the ratio is markedly small in the case of the nanodisks with an area of 4 × 104 nm2 or larger at B = −0.5 kG. The angle distribution of magnetization directions shows that the magnetization directions markedly tend to be parallel to the ridge directions of the hexagonal nanodisks, i.e., distribute in steps of ∼60° corresponding to the magnetic easy axes of the hexagonal NiAs-type crystal structure. The results suggest that the magnetic domains and coercive force can be tuned by controlling the MnAs nanodisk size.
Highlights
Device performance has been improved by the miniaturization of electronic devices in conventional Si complementary metal-oxide semiconductor (CMOS)-based integrated circuits
From the results reported in Ref. 15, single magnetic domain structures were mainly observed in the NDs with an area of 4× 104 nm2 or smaller, and multiple magnetic domain structures were predominant in the NDs with an area of 6 × 104 nm2 or larger
The magnetic domain structure in such a relatively large ND under as-grown condition could be unstable. (For example, for the NDs with an area between 4 × 104 and 5 × 104 nm2, the ratio of a single magnetic domain was estimated to be ∼44% under as-grown condition in Ref. 15.) Several reports insist that the increase in the sample length caused by a magnetostriction effect is observed in the MnAs and MnAsSb alloy systems27–30 and that the amount of a magnetostriction effect depends on the relationship between the crystal and magnetization orientations in MnAs and La0.8Sr0.2CoO3 alloys
Summary
Device performance has been improved by the miniaturization of electronic devices in conventional Si complementary metal-oxide semiconductor (CMOS)-based integrated circuits. A huge magnetoresistance up to 100 000% has been demonstrated in the MTJs with the granular GaAs:MnAs hybrid nanomaterial system consisting of ferromagnetic MnAs nanoclusters embedded in semiconducting GaAs layers.5 Such a MTJ structure has been mainly fabricated by conventional top–down-type microfabrication technologies. In the fabrication of such devices in the nanometer scale, these conventional approaches may possibly result in deterioration in device performance owing to process-induced damages and a relatively poor size-uniformity. To elude such possible problems, we have developed a bottom–up-type fabrication method, which is based on selectivearea metal–organic vapor phase epitaxy (SA-MOVPE), of ferromagnetic MnAs nanostructures on semiconducting GaAs (111)B and Si (111) substrates.. We believe that the results obtained in the current work lead to the control in the magnetic domain structures and a magnetization direction by tuning the ND size on Si substrates
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