An adaptive algorithm for n-body field expansions
Weinberg, Martin D.
1998-05-28
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The dynamics of the iron spins in YBa2(Cu(1-x)Fe(x))3O7 alloys (0 = to or less than 0.12) was studied by the means of inelastic neutron scattering. Measurements were performed using the time of flight technique with an excellent resolution of 50 micro eV, in a temperature range of 1.8 to 300 K. The doped samples show an elastic and a quasielastic intensity strongly varying with temperature. A spin glass like freezing is revealed at low temperature by a sudden decrease of the quasielastic intensity, an increase of the elastic or resolution limited intensity and a minimum in the quasielastic width. The freezing temperature corresponds to the one already determinated by a magnetic splitting in Mossbauer experiments. Above freezing, the occurrence of superconductivity slightly modifies the characteristics of the spin relaxation in the para...
Comment: 4 pages, 5 figures
Comment: 4 pages, 5 figures
Original paper from Mirebeau et al. PRL 83, 628, 1999 Comment from W. Bao et
al (cond-mat/0008042, 2 Aug 2000 submitted to PRL, updated on 1 sep 2000
Comment: 9 pages, 11 figures, submitted to Phys. Rev. B Subject: Strongly
Correlated Electrons Resubmission after referee's comments. Few typos also
involving an
We describe the evolution of the static and dynamic spin correlations of
La$_{1-x}$Ca$_x$MnO$_3$, for x=0.1, 0.125 and 0.2, where the system evolves
from the canted magnetic state towards the insulating ferromagnetic state,
approaching the metallic transition (x=0.22).
In the x=0.1 sample, the observation of two spin wave branches typical of two
distinct types of magnetic coupling, and of a modulation in the elastic diffuse
scattering characteristic of ferromagnetic inhomogeneities, confirms the static
and dynamic inhomogeneous features previously observed at x$<$0.1. The
anisotropic q-dependence of the intensity of the low-energy spin wave suggests
a bidimensionnal character for the static inhomogeneities. At x=0.125, which
corresponds to the occurence of a ferromagnetic and insulating state, the two
spin wave branches reduce to a ...
The ferromagnetic and insulating state observed in La$_{1-x}$Ca$_{x}$MnO$_3$,
0.125$<$x$<$0.2, is characterized by structural and magnetic anomalies below
T$_C$, similar to those observed in the x$_{Sr}$$\approx$1/8. A neutron
scattering study of the superlattice {\bf Q$_0$}= (0,0,1+/4)$_{cub}$ peak, and
of the magnetic excitations are reported in the x$_{Ca}$=0.2 sample. The
occurrence of this superstructure is associated with the observation of a gap
in the spin dynamics, at a {\bf q$_0$} wave-vector ({\bf q$_0$}={\bf
Q$_0$}-$\tau$) with the same modulus $|${\bf q$_0$}$|$ in all directions, which
divides the dispersion into two regimes. For $|${\bf q}$|$$<$$|${\bf q$_0$}$|$
the dispersion is splitted into two or three curves. For $|${\bf
q}$|$$>$$|${\bf q$_0$}$|$, magnetic excitations lock on acoustic and optic
phonon energies, rev...
