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Quantum Spin Fluctuations and magnons in antiferromagnetically coupled bilayers with tuneable intra-bilayer exchange - the case of Cr$_2$W(Te)O$_6$ | | Kingshuk Majumdar
; S. D. Mahanti
; | | Date: |
1 Sep 2015 | | Abstract: | Recent neutron diffraction studies have shown that in Cr$_2$(W,Te)O$_6$
systems, which consist of bilayers with strong antiferromagnetic inter-bilayer
coupling between Cr moments, the intra-bilayer coupling between the Cr moments
can be tuned from ferro (for W) to antiferro (for Te). {it Ab initio} density
functional calculations provide a microscopic understanding of the magnetic
structure but cannot explain the magnitude of the ordered Cr$^{3+}$ moments. In
order to understand the reduction of the ordered moment caused by quantum spin
fluctuations (QSF) we have studied the magnon dispersion and the sublattice
magnetization using a two parameter quantum Heisenberg spin Hamiltonian with
tunable intra-($j$) and antiferromagnetic inter- ($J$) bilayer couplings. In
the $j=0$ limit the system reduces to decoupled quantum dimers. The magnon
dispersion and normalized sublattice magnetization (NSM) have been calculated
using non-linear spin wave theory up to second-order corrections ($1/S^2$) in
spin $S$. The effect of $J$ is quite dramatic when $j$ is ferromagnetic, a
large peak in magnon dispersion appears at the corner of the Brillouin zone for
large $J$ (realistic case) in addition to changing the quadratic dispersion to
linear. Inelastic neutron scattering experiments can confirm this theoretical
prediction. The effect of $J$ on NSM is simple when $j$ is ferromagnetic, NSM
decreases monotonically with $J$. In contrast when $j$ is antiferromagnetic the
effect of $J$ is to suppress QSF effect until $Jsim j$ but further increase in
$J$ gives rise to increasing QSF reduction of the NSM. These theoretical
results are qualitatively consistent with experiment. | | Source: | arXiv, 1509.0101 | | Services: | Forum | Review | PDF | Favorites | |
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