Magnetic domain characterizations of anisotropic-shaped MnAs nanoclusters position-controlled by selective-area metal-organic vapor phase epitaxy

Abstract

The authors report the buildup fabrication and magnetic domain characterizations of anisotropic-shaped MnAs nanoclusters position-controlled on partially SiO 2 -masked GaAs ͑111͒B substrates by selective-area metal-organic vapor phase epitaxy. Magnetic force microscopy reveals that both the symmetric-and anisotropic-shaped nanoclusters show spontaneous magnetization at room temperature. Some of the nanoclusters show a single magnetic domain, in which magnetized directions are along one of the a-axes of NiAs-type MnAs, after the external magnetic fields up to 3500 Gauss are applied in-plane. The magnetic domains are well controlled by introducing both magnetocrystalline and shape magnetic anisotropies in the anisotropic-shaped nanoclusters. © 2009 American Institute of Physics. ͓DOI: 10.1063/1.3157275͔ Recent research activities for heteroepitaxial nanostructures of ferromagnet and III-V compound semiconductor ͑FM III-V hybrids͒ have gained much attention in the future nanospintronic device applications.1 It was reported that large tunneling magnetoresistance effect was shown in the MnAs/AlAs/MnAs heterostructures 2 and the GaAs:MnAs granular layers 3,4 above room temperature ͑RT͒, and that ferromagnetic NiAs-type MnAs layers served as an electrical spin injection source for semiconductors. 5 In recent theoretical calculations, in addition, it has been predicted that the electronic band-structure of hypothetical zinc-blende ͑ZB͒-type MnAs layers is half-metallic, which is promising nature for device applications.6-8 Thus far, conventional approaches to realizing nanospintronic devices using FM III-V hybrids have been mostly "top-down" fabrication techniques after the epitaxy because it has been necessary to grow the epitaxial ferromagnetic and semiconducting layers by molecular beam epitaxy at an extremely low growth temperature. [2][3][4][5]9

Comparison of the magnetic properties of GaInAs/MnAs and GaAs/MnAs hybrids with random and ordered arrangements of MnAs nanoclusters

“…The MnAs nanoclusters were then grown for 10 min at 825°C. 8 As for the samples with the randomly arranged nanoclusters the growth of the MnAs clusters leads to a p-doping of the insulating ͑111͒GaAs-substrate with Mn, also leading to paramagnetic behavior.…”

“…It can be seen that the nanoclusters assemble in the openings with a well defined orientation reflected by the formation of the crystal facets, i.e., crystal axes of the clusters and of the substrate are always oriented according to a fixed crystallographic relationship. 8 In particular, it can be seen that the clusters with the axis of elongation along ͗211͘ cannot reproduce the shape defined by the mask openings due to the faster growth rates on a-plane facets. Thus, it turns out that to obtain high-quality clusters with a large aspectratio defined by the mask openings in the SiO 2 , the mask openings must be orientated parallel to the ͗110͘ crystal direction of the substrate or equivalent directions arising from it by rotation by Ϯ120°about the ͗111͘ direction.…”

Magnetic Sensor Devices Based on Ordered Planar Arrangements of MnAs Nanocluster

“…For this purpose, we sandwich a small hexagon-shaped cluster between two elongated MnAs clusters. The reason for this geometry is that due to shape anisotropy the orientation in the elongated clusters is fixed whereas for the small cluster the orientation of the magnetization can be changed easily [6]. An important question is whether the transport across the two interfaces is coherent or incoherent.…”

“…The recently introduced selective-area metal-organic vapor-phase epitaxy (SAMOVPE) process offers novel ways of controlling size, shape, and position of MnAs clusters on the submicron scale [6], [7] and thus also to tune the magnetic properties of individual MnAs clusters. In particular, the clusters are grown with the c axis perpendicular to the substrate.…”

Selective-area growth and magnetic characterization of MnAs/AlGaAs nanoclusters on insulating Al2O3 layers crystallized on Si(111) substrates

“…SA-MOVPE is based on the bottom-up formation of single-crystalline ferromagnetic MnAs NCs on defined sites of semiconducting substrates. The SA-MOVPE is promising as it enables us to accurately adjust the size, shape, number, position, and spatial arrangement of the MnAs NCs [16][17][18][19] within the hybrids to tune its magnetic and magnetotransport properties. 3,[20][21][22] Ordered planar arrangements of coupled NCs show large MR effects 23 and MR ratios of 300% are predicted by theory.…”