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Griffiths phase in diluted magnetic semiconductors.
V M Galitski1, A Kaminski, S Das Sarma
1Condensed Matter Theory Center, Department of Physics, University of Maryland, College Park, MD 20742-4111, USA.
Physical Review Letters
|June 1, 2004
Summary
Disorder near ferromagnetic transitions in diluted magnetic semiconductors creates a Griffiths phase. This phase affects dynamic susceptibility, with critical exponents linked to percolation indices.
Area of Science:
- Condensed matter physics
- Magnetism and magnetic materials
- Disordered systems
Background:
- Diluted magnetic semiconductors exhibit complex magnetic behaviors.
- Understanding ferromagnetic transitions in disordered systems is crucial.
- The strongly localized regime presents unique theoretical challenges.
Purpose of the Study:
- To investigate the impact of disorder on ferromagnetic transitions.
- To explore the emergence of the Griffiths phase.
- To analyze the nonperturbative effects on dynamic susceptibility.
Main Methods:
- Derivation of an effective polaron Hamiltonian.
- Analysis of Griffiths-McCoy effects.
- Explicit derivation of long-time susceptibility.
Main Results:
- An effective polaron Hamiltonian was derived.
- The Griffiths phase was identified above the ferromagnetic transition point.
- Nonperturbative contributions to dynamic susceptibility were found.
Conclusions:
- The Griffiths-McCoy effects significantly influence dynamic susceptibility.
- The long-time susceptibility exhibits a pseudoscaling form.
- The dynamic critical exponent is determined by percolation indices.