Magnetoresistance in ferromagnetic metal/ferromagnetic semiconductor micro-structures

We use SQUID magnetometry and circular contacts to study the magnetoresistance in GaMnAs/Py bilayer structures. Our magnetization hysteresis loops show that there is no measurable coupling between the two ferromagnetic layers, even though they are not separated by any nano-magnetic spacer layers. Furthermore, the field-dependent magnetization shows a rich behavior that depends on the width of the GaMnAs in the circular structures. Samples with the narrowest gaps show a magnetoresistance effect that seems to be due to the tunneling magnetoresistance at the interface between py and GaMnAs.