Parametric pumping and kinetics of magnons in dipolar ferromagnets
- Institut fuer Theoretische Physik, Universitaet Frankfurt, Max-von-Laue Strasse 1, 60438 Frankfurt (Germany)
The time evolution of magnons subject to a time-dependent microwave field is usually described within the so-called 'S-theory', where kinetic equations for the distribution function are obtained within the time-dependent Hartree-Fock approximation. To explain the recent observation of 'Bose-Einstein condensation of magnons' in an external microwave field [Demokritov et al., Nature (London) 443, 430 (2006)], we extend the S-theory to include the Gross-Pitaevskii equation for the time-dependent expectation values of the magnon creation and annihilation operators. We explicitly solve the resulting coupled equations within a simple approximation where only a single condensed mode is retained. We also re-examine the usual derivation of an effective boson model from a realistic spin model for yttrium-iron garnet films and argue that in the parallel pumping geometry (where both the static and the time-dependent magnetic field are parallel to the macroscopic magnetization) the time-dependent Zeemann energy cannot give rise to magnon condensation.
- OSTI ID:
- 21366699
- Journal Information:
- Physical Review. B, Condensed Matter and Materials Physics, Vol. 81, Issue 10; Other Information: DOI: 10.1103/PhysRevB.81.104308; (c) 2010 The American Physical Society; ISSN 1098-0121
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANNIHILATION OPERATORS
BOSE-EINSTEIN CONDENSATION
BOSONS
DISTRIBUTION FUNCTIONS
EVOLUTION
FERRITE GARNETS
FILMS
HARTREE-FOCK METHOD
KINETIC EQUATIONS
KINETICS
MAGNETIC FIELDS
MAGNETIZATION
MAGNONS
MICROWAVE RADIATION
SPIN
TIME DEPENDENCE
YTTRIUM COMPOUNDS
ANGULAR MOMENTUM
APPROXIMATIONS
CALCULATION METHODS
ELECTROMAGNETIC RADIATION
EQUATIONS
FUNCTIONS
MATHEMATICAL OPERATORS
MINERALS
OXIDE MINERALS
PARTICLE PROPERTIES
QUANTUM OPERATORS
QUASI PARTICLES
RADIATIONS
TRANSITION ELEMENT COMPOUNDS