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Exchange coupling at ferromagnet/semiconductor interface

Authors Zhang, Tao
Issue Date 2011
Summary Due to its decisive role played in spin injection and detection, interface property of a ferromagnetic metal and a semiconductor is of fundamental importance for spintronics. In this thesis, five kinds of Fe-semiconductor (111) bilayer systems, namely, Fe/GaAs(111)A&B, Fe/ZnSe(111)B, Fe/GaP(111)B, Fe/ZnS(111)B and Fe/Si(111), with various Fe growth temperature and thickness are fabricated using molecular beam epitaxy. Superconducting quantum interference device magnetometer is adapted to measure the magnetization hysteresis loop of these bilayers from 1.8 K to 350 K. After in plane field cooling procedure from 200 K to 1.8 K, a unidirectional exchange anisotropy, i.e. exchange bias (EB) are observed in all above mentioned samples at low temperature, indicating there are new magnetic phases in these Fe-semiconductor (111) bilayer samples. It is proposed that atomic interdiffusion occurred at these interfaces results in these new magnetic phases, which are Fe-As, Fe-Se, Fe-P, Fe-S and Fe-Si complex formed at the interface. The interface energy is found ranging from 0.041 to 0.131 erg/cm2. As temperature increases, the EB effect disappears at the so-called blocking temperature (TB). For all the samples studied, TB varies from 20 to 52 K. Other EB related effects, which have been observed in other typical antiferromagnet (AFM)/ ferromagnet (FM) bilayer systems, are also observed as detailed below. In both Fe/GaAs(111)A and Fe/GaAs(111)B bilayer samples, unidirectional coercivity enhancement (UCE), training effect and training related asymmetry of magnetization are observed. It is also found that magnetic field sweep at 350 K can induce further iron atoms diffuse into GaAs in Fe/GaAs(111)A sample, which effectively increase the thickness of AFM interdiffusion layer while decrease the thickness of FM iron layer. Three Fe/ZnSe(111)B bilayer samples with varying growth temperature and/or thickness of Fe films are investigated. Besides the changing of TB among three samples, a paramagnetic phase Fe is indentified in a low temperature (130 oC) grown thin iron film sample (2.5 nm). For Fe/GaP(111)B, Fe/ZnS(111)B and Fe/Si(111) bilayers, EB effect with different TB are observed. Like its chalcogenide counterpart with same growth parameters, Fe/ZnS(111)B bilayer also demonstrates a paramagnetic phase iron.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2011
Language English
Format Thesis
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