3,359 research outputs found
Ferromagnetic insulating phase in Pr{1-x}Ca{x}MnO3
A ferromagnetic insulating (FM-I) state in Pr0.75Ca0.25MnO3 has been studied
by neutron scattering experiment and theoretical calculation. The insulating
behavior is robust against an external magnetic field, and is ascribed to
neither the phase separation between a ferromagnetic metallic (FM-M) phase and
a non-ferromagnetic insulating one, nor the charge ordering. We found that the
Jahn-Teller type lattice distortion is much weaker than PrMnO3 and the magnetic
interaction is almost isotropic. These features resembles the ferromagnetic
metallic state of manganites, but the spin exchange interaction J is much
reduced compared to the FM-M state. The theoretical calculation based on the
staggered type orbital order well reproduces several features of the spin and
orbital state in the FM-I phase.Comment: REVTeX4, 10 pages, 9 figure
Spin Dynamics of Double-Exchange Manganites with Magnetic Frustration
This work examines the effects of magnetic frustration due to competing
ferromagnetic and antiferromagnetic Heisenberg interactions on the spin
dynamics of the double-exchange model. When the local moments are non-colinear,
a charge-density wave forms because the electrons prefer to sit on lines of
sites that are coupled ferromagnetically. With increasing hopping energy, the
local spins become aligned and the average spin-wave stiffness increases. Phase
separation is found only within a narrow range of hopping energies. Results of
this work are applied to the field-induced jump in the spin-wave stiffness
observed in the manganite PrCaMnO with .Comment: 10 pages, 3 figure
Anomalous ferromagnetic spin fluctuations in an antiferromagnetic insulator Pr_{1-x}Ca_{x}MnO_{3}
The high temperature paramagnetic state in an antiferromagnetic (AFM)
insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin
fluctuations with an anomalously small energy scale. The FM fluctuations show a
precipitous decrease of the intensity at the charge ordering temperature
T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature
T_{N}. These results demonstrate the importance of the spin ordering for the
complete switching of the FM fluctuation in doped manganites.Comment: REVTeX, 5 pages, 4 figures, submitted to Phys. Rev.
Spin Dynamics of a Canted Antiferromagnet in a Magnetic Field
The spin dynamics of a canted antiferromagnet with a quadratic spin-wave
dispersion near \vq =0 is shown to possess a unique signature. When the
anisotropy gap is negligible, the spin-wave stiffness \dsw (\vq, B) =
(\omega_{\vq}-B)/q^2 depends on whether the limit of zero field or zero
wavevector is taken first. Consequently, \dsw is a strong function of
magnetic field at a fixed wavevector. Even in the presence of a sizeable
anisotropy gap, the field dependence of both \dsw and the gap energy
distinguishes a canted antiferromagnet from a phase-separated mixture
containing both ferromagnetic and antiferromagnetic regions.Comment: 10 pages, 3 figure
Time Dependent Effects and Transport Evidence for Phase Separation in La_{0.5}Ca_{0.5}MnO_{3}
The ground state of La_{1-x}Ca_{x}MnO_{3} changes from a ferromagnetic
metallic to an antiferromagnetic charge-ordered state as a function of Ca
concentration at x ~ 0.50. We present evidence from transport measurements on a
sample with x = 0.50 that the two phases can coexist, in agreement with other
observations of phase separation in these materials. We also observe that, by
applying and then removing a magnetic field to the mainly charge-ordered state
at some temperatures, we can "magnetically anneal" the charge order, resulting
in a higher zero-field resistivity. We also observe logarithmic time dependence
in both resistivity and magnetization after a field sweep at low temperatures.Comment: 9 pages, LATEX, 3 postscript figure
Commensurate-Incommensurate transition in the melting process of the orbital ordering in Pr0.5Ca0.5MnO3: neutron diffraction study
The melting process of the orbital order in
Pr0.5Ca0.5MnO3 single crystal has been studied in detail as a function of
temperature by neutron diffraction. It is demonstrated that a
commensurate-incommensurate (C-IC) transition of the orbital ordering takes
place in a bulk sample, being consistent with the electron diffraction studies.
The lattice structure and the transport properties go through drastic changes
in the IC orbital ordering phase below the charge/orbital ordering temperature
Tco/oo, indicating that the anomalies are intimately related to the partial
disordering of the orbital order, unlike the consensus that it is related to
the charge disordering process. For the same T range, partial disorder of the
orbital ordering turns on the ferromagnetic spin fluctuations which were
observed in a previous neutron scattering study.Comment: 5 pages, 2 figures, REVTeX, to be published in Phys. Rev.
- …