3,603 research outputs found
First-order transition in the itinerant ferromagnet CoSSe
Undoped CoS is an isotropic itinerant ferromagnet with a continuous or
nearly continuous phase transition at K. In the doped
CoSSe system, the Curie temperature is lowered to K, and the transition becomes clearly first order in nature. In particular
we find a discontinuous evolution of the spin dynamics as well as strong time
relaxation in the ferromagnetic Bragg intensity and small angle neutron
scattering in vicinity of the ferromagnetic transition. In the ordered state
the long-wavelength spin excitations were found to be conventional
ferromagnetic spin-waves with negligible spin-wave gap ( meV),
indicating that this system is also an excellent isotropic (soft) ferromagnet.
In a wide temperature range up to , the spin-wave stiffness
follows the prediction of the two-magnon interaction theory, , with meV-\AA. The stiffness,
however, does not collapse as from below. Instead a
quasielastic central peak abruptly develops in the excitation spectrum, quite
similar to results found in the colossal magnetoresistance oxides such as
(La-Ca)MnO.Comment: 8pages, 8figure
Spin-Coupled Local Distortions in Multiferroic Hexagonal HoMnO3
Local structural measurements have been performed on hexagonal HoMnO3 in
order to ascertain the specific changes in bond distances which accompany
magnetic ordering transitions. The transition from paramagnetic to the
antiferromagetic (noncollinear) phase near ~70 K is dominated by changes in the
a-b plane Mn-Mn bond distances. The spin rotation transition near ~40 K
involves both Mn-Mn and nearest neighbor Ho-Mn interactions while the low
temperature transition below 10 K involves all interactions, Mn-Mn, Ho-Mn
(nearest and next nearest) and Ho-Ho correlations. These changes in bond
distances reveal strong spin-lattice coupling. The similarity in magnitude of
the change in J(Mn-Mn) and J(Ho-Mn) enhances the system frustration. The
structural changes are interpreted in terms of a model of competing spin order
and local structural distortions. Density functional calculations are used to
estimate the energies associated with ionic displacements. The calculations
also reveal asymmetric polarization of the charge density of Ho, O3 and O4
sites along the z-axis in the ferroelectric phase. This polarization
facilitates coupling between Ho atoms on neighboring planes normal to the
z-axis.Comment: 8 figure
Spin-lattice order in frustrated ZnCr2O4
Using synchrotron X-rays and neutron diffraction we disentangle spin-lattice
order in highly frustrated ZnCrO where magnetic chromium ions occupy
the vertices of regular tetrahedra. Upon cooling below 12.5 K the quandary of
anti-aligning spins surrounding the triangular faces of tetrahedra is resolved
by establishing weak interactions on each triangle through an intricate lattice
distortion. The resulting spin order is however, not simply a N\'{e}el state on
strong bonds. A complex co-planar spin structure indicates that antisymmetric
and/or further neighbor exchange interactions also play a role as ZnCrO
resolves conflicting magnetic interactions
Spin freezing and dynamics in Ca_{3}Co_{2-x}Mn_{x}O_{6} (x ~ 0.95) investigated with implanted muons: disorder in the anisotropic next-nearest neighbor Ising model
We present a muon-spin relaxation investigation of the Ising chain magnet
Ca_{3}Co_{2-x}Mn_{x}O_{6} (x~0.95). We find dynamic spin fluctuations
persisting down to the lowest measured temperature of 1.6 K. The previously
observed transition at around T ~18 K is interpreted as a subtle change in
dynamics for a minority of the spins coupling to the muon that we interpret as
spins locking into clusters. The dynamics of this fraction of spins freeze
below a temperature T_{SF}~8 K, while a majority of spins continue to
fluctuate. An explanation of the low temperature behavior is suggested in terms
of the predictions of the anisotropic next-nearest-neighbor Ising model.Comment: 4 pages, 2 figure
Evidences of a consolute critical point in the Phase Separation regime of La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single crystals
We report on DC and pulsed electric field sensitivity of the resistance of
mixed valent Mn oxide based La(5/8-y)Pr(y)Ca(3/8)MnO(3) (y = 0.4) single
crystals as a function of temperature. The low temperature regime of the
resistivity is highly current and voltage dependent. An irreversible transition
from high (HR) to a low resistivity (LR) is obtained upon the increase of the
electric field up to a temperature dependent critical value (V_c). The
current-voltage characteristics in the LR regime as well as the lack of a
variation in the magnetization response when V_c is reached indicate the
formation of a non-single connected filamentary conducting path. The
temperature dependence of V_c indicates the existence of a consolute point
where the conducting and insulating phases produce a critical behavior as a
consequence of their separation.Comment: 5 pages, 6 figures, corresponding author: C. Acha ([email protected]
A Comparison of the High-Frequency Magnetic Fluctuations in Insulating and Superconducting La2-xSrxCuO4
Inelastic neutron scattering performed at a spallation source is used to make
absolute measurements of the dynamic susceptibility of insulating La2CuO4 and
superconducting La2-xSrxCuO4 over the energy range 15<EN<350 meV. The effect of
Sr doping on the magnetic excitations is to cause a large broadening in
wavevector and a substantial change in the spectrum of the local spin
fluctuations. Comparison of the two compositions reveals a new energy scale of
22 meV in La1.86Sr0.14CuO4.Comment: RevTex, 7 Pages, 4 postscript figure
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