In (Ga,Mn)As, the manganese atoms provide a magnetic moment, and each also acts as an acceptor, making it a p-type material.
In (Ga,Mn)As the manganese substitute into gallium sites in the GaAs crystal and provide a magnetic moment.
Because manganese has a low solubility in GaAs, incorporating a sufficiently high concentration for ferromagnetism to be achieved proves challenging.
At lower temperatures, around 250 °C, there is insufficient thermal energy for surface segregation to occur but still sufficient for a good quality single crystal alloy to form.
[20][21][22][23][24] In addition to this, as molecular beam epitaxy techniques and equipment are refined and improved it is hoped that greater control over growth conditions will allow further incremental advances in the Curie temperature of (Ga,Mn)As.
Regardless of the fact that room-temperature ferromagnetism has not yet been achieved, magnetic semiconductors materials such as (Ga,Mn)As, have shown considerable success.
Using the gate action to either deplete or accumulate holes in the channel it was possible to change the characteristic of the Hall response to be either that of a paramagnet or of a ferromagnet.
The combining of magnetic and electronic functionality demonstrated by this experiment is one of the goals of spintronics and may be expected to have a great technological impact.
This is again of potential technological interest as it shows the possibility that the spin states in non-magnetic semiconductors can be manipulated without the application of a magnetic field.
Both positive[32] and negative[33] values of domain wall resistance have been reported, leaving this an open area for future research.
While the device operated in a diffusive regime the constrictions would pin domain walls, resulting in a giant magnetoresistance signal.
[35] It was demonstrated in reference[36] using a lateral (Ga,Mn)As device containing three regions which had been patterned to have different coercive fields, allowing the easy formation of a domain wall.
This experiment showed that the current required to achieve this reversal in (Ga,Mn)Aswas two orders of magnitude lower than that of metal systems.
This effect arises from the intricate dependence of the tunnelling density of states on the magnetization, and can result in magnetoresistance of several orders of magnitude.