Recent acheivement on diluted magnetic semiconductor and new perspective of magnetoresistive sensor

Antisymmetric magneto-resistance anomalies generated by a reversal of the magnetization are studied in a number of GaMnAs/InGaAs layers with out-of-plane (easy axis) magnetization. The anomalies occur independent of the magnetic field orientation. This shows, that once a magnetic domain with reversed magnetization is nucleated, simply the presence of the domain wall between the longitudinal contacts is sufficient to give rise to the anomaly. Very different shapes for magneto-resistance anomaly can be observed experimentally depending upon the sample. They reflect the various magnetic domain structures present inside the layers during the magnetization reversal process.

GaAs:Mn nanowires were obtained on GaAs(001) and GaAs(111)B substrates by molecular beam epitaxial growth of (Ga,Mn)As at conditions leading to MnAs phase separation. Their density is proportional to the density of catalyzing MnAs nanoislands, which can be controlled by the Mn flux and/or the substrate temperature. After deposition corresponding to a 200 nm thick (Ga,Mn)As layer the nanowires are around 700 nm long. Their shapes are tapered, with typical diameters around 30 nm at the base and 7 nm at the tip. The wires grow along the 111) direction, i.e., along the surface normal on GaAs(111)B and inclined on GaAs(001). In the latter case they tend to form branches. Being rooted in the ferromagnetic semiconductor (Ga,Mn)As, the nanowires combine one-dimensional properties with the magnetic properties of (Ga,Mn)As and provide natural, self-assembled structures for nanospintronics.

The planar Hall effect was used for investigation of magnetic anisotropy in short period (Ca,Mn)As/CaAs superlattices epitaxially grown on (001) oriented GaAs substrate. The results confirmed the existence of low-temperature magneto crystalline anisotropy in the superlattices with the easy magnetic axes directed along the two in-plane (100) directions. Attention is paid to the two-state behaviour of the planar Hall resistance at zero magnetic field that provides its usefulness for applications in non-volatile memory devices.

We analyse the role of structural defects in GaMnAs and demonstrate how their density can be drastically reduced by in situ post-growth annealing under As capping. Modifications of the magnetic, transport, and structural properties of annealed GaMnAs layers are presented. The main result is that Curie temperatures are strongly increased relative to those of as-grown layers, typically from 70-80 K to 150-160 K. The annealed layers exhibit well-ordered smooth surfaces, suitable for further epitaxial overgrowth.

We have performed a systematic investigation of the so-called planar Hall effect and the magnetization in thin layer of ferromagnetic Ga0.94Mn0.06As semiconductor, which has been subjected to post-growth annealing. The annealing process was performed under As capping in order to achieve high hole concentration exceeding 10(21) cm(-1) and high Curie temperature of 125 K. At liquid helium temperature the planar Hall effect in the layer exhibits a giant magnitude, several orders of magnitude greater than analogous effect found in metallic ferromagnets. When sweeping the magnetic field the planar Hall resistance varies non-monotonously alternating its sign and displaying the appearance of single or double hysteresis loops, depending on the magnetic field orientation and the sweeping range of the magnetic field. It is demonstrated, by comparing with the magnetization data, that the planar Hall effect reproduces the complex behaviour of the magnetic anisotropy of the layer grown under biaxial compressive strain, which additionally displays uniaxial in-plane magnetization anisotropy. (c) 2006 Elsevier B.V. All rights reserved.

Transport and magnetic properties of CezLa1-zFe4Sb12 have been investigated in the whole range of substitution 0