, Korea University
[Host: Seung-Hun Lee]
The spintronics technology requires materials that allow simultaneous control of the charge and the spin degrees of freedom. Recent efforts dedicated in search of such materials have led us to the successful fabrication of artificial ferromagnetic semiconductor GaMnAs, where doping of magnetic Mn2+ ions into insulating GaAs results in robust ferromagnetism and semiconducting property at the same time. In order to realize useful devices from magnetic semiconductors, however, it is important to be able to control not only the magnetic properties of individual layers but also interactions between them. Previously the interactions between ferromagnetic GaMnAs layers across nonmagnetic GaAs spacers have been observed to be ferromagnetic only. Since the RKKY interaction in metallic magnetic multilayers is known to produce exchange oscillations between ferromagnetic and antiferromagnetic (AFM) as a function of layer thickness, AFM interlayer exchange coupling has been expected to be attainable also in semiconductor-based multilayers by enhancing carrier concentrations in the spacers.
To test this idea, we have fabricated GaMnAs-based multilayers with different carrier concentrations and thicknesses in the spacers. Molecular beam epitaxy was used to deposit 10 periods of Ga0.97Mn0.03As/GaAs on GaAs (001) substrates. In order to increase the carrier concentration of selected samples, Be doping at the concentration of 1.2 x 1020 cm-3 was introduced in the nonmagnetic spacer. Using polarized neutron reflectivity, we indeed observed and confirmed the occurrence of antiferromagnetic interlayer coupling in some of the samples with Be-doped spacers. Their field cycling behavior clearly indicated that the observed antiferromagnetic coupling is spontaneous and robust. All of these samples showed GMR-like transitions in magnetotransport measurements. In contrast, none of the samples without Be-doped spacers showed such behavior. These results indicate that the interlayer exchange couplings in GaMnAs-based ferromagnetic multilayers can be controlled via engineering of the spacer properties.
Condensed Matter Seminar
Thursday, November 11, 2010
Physics Building, Room 204
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