Magnetism in MnxGe1-x Semiconductors Mediated by Impurity Band Carriers
- ORNL
- Vanderbilt University
We present a comprehensive study of ferromagnetism and magnetotransport in Mn-doped germanium, grown with molecular-beam epitaxy. Ferromagnetism in Mn{sub x}Ge{sub 1-x} (0 < x < 0.09) is characterized by two different ordering temperatures T{sub c} and T*{sub c} with T{sub c}-T*{sub c}. The onset of global ferromagnetic order at T{sub c} coincides with the percolation threshold for (activated) charge transport. Magnetism between T{sub c} and T*{sub c} originates from 'clustered dopants' associated with inhomogeneities. The ferromagnetic ordering temperature within the clusters is of order T*{sub c} while the coupling between the clusters is mediated by thermally activated carriers moving in an impurity band. The magnetoresistance exhibits nonmonotonic temperature and magnetic field dependence; both negative and positive magnetoresistance contributions are observed. The anomalous Hall effect between T{sub c} and T*{sub c} appears to be influenced heavily by the large magnetoresistance. The normal and anomalous Hall coefficients both diverge at low temperature. All these observations indicate that Mn{sub x}Ge{sub 1-x} is most adequately described within an impurity band model where the ratio J/t of the Mn hole exchange J and hole hopping t is large.
- Research Organization:
- Oak Ridge National Laboratory (ORNL)
- Sponsoring Organization:
- ORNL LDRD Seed-Money
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 976000
- Journal Information:
- Physical Review B, Journal Name: Physical Review B Journal Issue: 19 Vol. 72; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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