37 research outputs found
S-mixing and quantum tunneling of the magnetization in molecular nanomagnets
The role of -mixing in the quantum tunneling of the magnetization in
nanomagnets has been investigated. We show that the effect on the tunneling
frequency is huge and that the discrepancy (more than 3 orders of magnitude in
the tunneling frequency) between spectroscopic and relaxation measurements in
Fe can be resolved if -mixing is taken into account.Comment: REVTEX, 10 pages, 3 jpg figures, to appear in PR
NMR as a probe of the relaxation of the magnetization in magnetic molecules
We investigate the time autocorrelation of the molecular magnetization
for three classes of magnetic molecules (antiferromagnetic rings, grids and
nanomagnets), in contact with the phonon heat bath. For all three classes, we
find that the exponential decay of the fluctuations of , associated with
the irreversible exchange of energy with the heat bath, is characterized by a
single characteristic time for not too high temperature and
field . This is reflected in a nearly single-lorentzian shape of the
spectral density of the fluctuations. We show that such fluctuations are
effectively probed by NMR, and that our theory explains the recent
phenomenological observation by Baek et al. (PRB70, 134434) that the
Larmor-frequency dependence of data in a large number of AFM rings fits
to a single-lorentzian form.Comment: Published as Phys. Rev. Letters 94, 077203 (2005) in slightly reduced
for
Spin dynamics of heterometallic Cr7M wheels (M = Mn, Zn, Ni) probed by inelastic neutron scattering
Inelastic neutron scattering has been applied to the study of the spin
dynamics of Cr-based antiferromagnetic octanuclear rings where a finite total
spin of the ground state is obtained by substituting one Cr(III) ion (s = 3/2)
with Zn (s = 0), Mn (s = 5/2) or Ni (s = 1) di-cations. Energy and intensity
measurements for several intra-multiplet and inter-multiplet magnetic
excitations allow us to determine the spin wavefunctions of the investigated
clusters. Effects due to the mixing of different spin multiplets have been
considered. Such effects proved to be important to correctly reproduce the
energy and intensity of magnetic excitations in the neutron spectra. On the
contrary to what is observed for the parent homonuclear Cr8 ring, the symmetry
of the first excited spin states is such that anticrossing conditions with the
ground state can be realized in the presence of an external magnetic field.
Heterometallic Cr7M wheels are therefore good candidates for macroscopic
observations of quantum effects.Comment: 9 pages, 11 figures, submitted to Phys. Rev. B, corrected typos and
added references, one sentence change
Bistability, multistability and nonreciprocal light propagation in Thue-Morse multilayered structures
The nonlinear properties of quasiperiodic photonic crystals based on the
Thue-Morse sequence are investigated. The intrinsic spatial asymmetry of these
one-dimensional structures for odd generation numbers results in bistability
thresholds which are sensitive to the propagation direction. Along with
resonances of perfect transmission, this feature allows to achieve strongly
non-reciprocal propagation and to create an all-optical diode. The salient
qualitative features of such optical diode action is readily explained through
a simple coupled resonator model. The efficiency of a passive scheme, which
does not necessitate of an additional short pump signal, is compared to an
active scheme, where such a signal is required.Comment: 18 pages, 8 figure