1,316 research outputs found
Simple theory for spin-lattice relaxation in metallic rare earth ferromagnets
The spin-lattice relaxation time is a key quantity both for the
dynamical response of ferromagnets excited by laser pulses and as the speed
limit of magneto-optical recording. Extending the theory for the electron
paramagnetic resonance of magnetic impurities to spin-lattice relaxation in
ferromagnetic rare earths we calculate for Gd and find a value of
48 ps in very good agreement with time-resolved spin-polarized photoemission
experiments. We argue that the time scale for in metals is
essentially given by the spin-orbit induced magnetocrystalline anisotropy
energy.Comment: 18 pages revtex, 5 uuencoded figure
ESR and spin-lattice relaxation of Nd3+ in a metallic host: LaRh2
We report the first ESR observation of Nd3+ in a metal: cubic LaRh2. The resonance arises from a Γ6 ground state and exhibits hyperfine splitting at low temperature, allowing for positive identification. Above about 12 K, the ESR linewidth increases exponentially with temperature. We attribute this increase to the resonance phonon relaxation process involving the first excited state at 125±10 K
Magnetocaloric Study of Spin Relaxation in `Frozen' Dipolar Spin Ice Dy2Ti2O7
The magnetocaloric effect of polycrystalline samples of pure and Y-doped
dipolar spin ice Dy2Ti2O7 was investigated at temperatures from nominally 0.3 K
to 6 K and in magnetic fields of up to 2 T. As well as being of intrinsic
interest, it is proposed that the magnetocaloric effect may be used as an
appropriate tool for the qualitative study of slow relaxation processes in the
spin ice regime. In the high temperature regime the temperature change on
adiabatic demagnetization was found to be consistent with previously published
entropy versus temperature curves. At low temperatures (T < 0.4 K) cooling by
adiabatic demagnetization was followed by an irreversible rise in temperature
that persisted after the removal of the applied field. The relaxation time
derived from this temperature rise was found to increase rapidly down to 0.3 K.
The data near to 0.3 K indicated a transition into a metastable state with much
slower relaxation, supporting recent neutron scattering results. In addition,
magnetic dilution of 50 % concentration was found to significantly prolong the
dynamical response in the milikelvin temperature range, in contrast with
results reported for higher temperatures at which the spin correlations are
suppressed. These observations are discussed in terms of defects and loop
correlations in the spin ice state.Comment: 9 figures, submitted to Phys. Rev.
Full Aging in Spin Glasses
The discovery of memory effects in the magnetization decays of spin glasses
in 1983 began a large effort to determine the exact nature of the decay. While
qualitative arguments have suggested that the decay functions should scale as
, the only time scale in the system, this type of scaling has not yet
been observed. In this letter we report strong evidence for the scaling of the
TRM magnetization decays as a function of . By varying the rate and the
profile that the sample is cooled through its transition temperature to the
measuring temperature, we find that the cooling plays a major role in
determining scaling. As the effective cooling time decreases, scaling improves and for we find almost perfect
scaling. We also find that subtraction of a stationary term
from the magnetization decay has a small effect on the scaling but changes the
form of the magnetization decay and improves overlap between curves produced
with different .Comment: 4 pages, 3 figure
Magnons and factons in diluted antiferromagnets (invited)
Version of RecordPublishe
Anharmonic Decay of Vibrational States in Amorphous Silicon
Anharmonic decay rates are calculated for a realistic atomic model of
amorphous silicon. The results show that the vibrational states decay on
picosecond timescales and follow the two-mode density of states, similar to
crystalline silicon, but somewhat faster. Surprisingly little change occurs for
localized states. These results disagree with a recent experiment.Comment: 10 pages, 4 Postscript figure
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