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Double exchange in a magnetically frustrated system
- Source :
- Journal of Physics: Condensed Matter. 16:5483-5501
- Publication Year :
- 2004
- Publisher :
- IOP Publishing, 2004.
-
Abstract
- This work examines the magnetic order and spin dynamics of a double-exchange model with competing ferromagnetic and antiferromagnetic Heisenberg interactions between the local moments. The Heisenberg interactions are periodically arranged in a Villain configuration in two dimensions with nearest-neighbor, ferromagnetic coupling $J$ and antiferromagnetic coupling $-\eta J$. This model is solved at zero temperature by performing a $1/\sqrt{S}$ expansion in the rotated reference frame of each local moment. When $\eta $ exceeds a critical value, the ground state is a magnetically frustrated, canted antiferromagnet. With increasing hopping energy $t$ or magnetic field $B$, the local moments become aligned and the ferromagnetic phase is stabilized above critical values of $t$ or $B$. In the canted phase, a charge-density wave forms because the electrons prefer to sit on lines of sites that are coupled ferromagnetically. Due to a change in the topology of the Fermi surface from closed to open, phase separation occurs in a narrow range of parameters in the canted phase. In zero field, the long-wavelength spin waves are isotropic in the region of phase separation. Whereas the average spin-wave stiffness in the canted phase increases with $t$ or $\eta $, it exhibits a more complicated dependence on field. This work strongly suggests that the jump in the spin-wave stiffness observed in Pr$_{1-x}$Ca$_x$MnO$_3$ with $0.3 \le x \le 0.4$ at a field of 3 T is caused by the delocalization of the electrons rather than by the alignment of the antiferromagnetic regions.<br />Comment: 28 pages, 12 figures
- Subjects :
- Physics
Condensed Matter - Materials Science
Strongly Correlated Electrons (cond-mat.str-el)
Field (physics)
Condensed matter physics
Materials Science (cond-mat.mtrl-sci)
FOS: Physical sciences
Fermi surface
Condensed Matter Physics
Coupling (probability)
Magnetic field
Condensed Matter - Strongly Correlated Electrons
Ferromagnetism
Spin wave
Antiferromagnetism
Condensed Matter::Strongly Correlated Electrons
General Materials Science
Ground state
Subjects
Details
- ISSN :
- 1361648X and 09538984
- Volume :
- 16
- Database :
- OpenAIRE
- Journal :
- Journal of Physics: Condensed Matter
- Accession number :
- edsair.doi.dedup.....2da29eb962ed5eee1593d3f013dd01cd