73 research outputs found
Exchange integrals and magnetization distribution in BaCu2X2O7 (X=Ge,Si)
Estimating the intrachain and interchain exchange constants in BaCu2X2O7
(X=Ge,Si) by means of density-functional calculations within the local
spin-density approximation (LSDA) we find the Ge compound to be a more ideal
realization of a one-dimensional spin chain with Dzyaloshinskii-Moriya
interaction than its Si counterpart. Both compounds have a comparable magnitude
of interchain couplings in the range of 5-10 K, but the nearest neighbor
intrachain exchange of the Ge compound is nearly twice as large as for the Si
one. Using the LSDA+U method we predict the detailed magnetization density
distribution and especially remarkable magnetic moments at the oxygen sites
Temperature- and Size-dependence of Line shape of ESR spectra of XXZ antiferromagnetic chain
The ESR (Electron Spin Resonance) spectrum of the XXZ spin chain with finite
length shows a double-peak structure at high temperatures around the EPR
(Electron Paramagnetic Resonance) resonance frequency. This fact has been
pointed out by direct numerical methods (S. El Shawish, O. Cepas and S.
Miyashita; H. Ikeuchi, H. De Raedt, S. Bertaina and S. Miyashita). On the other
hand, at low temperatures the spectrum has a single peak with a finite shift
from the frequency of EPR as predicted by the analysis of field theoretical
works (M. Oshikawa and I. Affleck). We study how the spectrum changes with the
temperature, and also we study the size-dependence of the line shape including
the even-odd effect. In order to understand those dependences, we introduce a
decomposition of the spectrum into contributions from transitions specified by
magnetization, and we characterize the structure of the spectrum by individual
contributions. Applying the moment method introduced by M. Brockman et al., to
each component, we analyze the size-dependence of the structure of the
spectrum, which supports the numerical observation that separation of the
double-peak structure vanishes inversely with the size.Comment: 11 pages, 10 figure
Spin-Orbit Qubits of Rare-Earth-Metal Ions in Axially Symmetric Crystal Fields
Contrary to the well known spin qubits, rare-earth qubits are characterized
by a strong influence of crystal field due to large spin-orbit coupling. At low
temperature and in the presence of resonance microwaves, it is the magnetic
moment of the crystal-field ground-state which nutates (for several s) and
the Rabi frequency is anisotropic. Here, we present a study of the
variations of with the magnitude and direction of the
static magnetic field for the odd Er isotope in a single
crystal CaWO:Er. The hyperfine interactions split the
curve into eight different curves which are fitted
numerically and described analytically. These "spin-orbit qubits" should allow
detailed studies of decoherence mechanisms which become relevant at high
temperature and open new ways for qubit addressing using properly oriented
magnetic fields
Rabi oscillations of solitons in spin-chains: a new route to quantum computation and communication
We provide the first evidence for coherence and Rabi oscillations of
spin-solitons pinned by the local breaking of translational symmetry in
isotropic Heisenberg chains (simple antiferromagnetic-N\'{e}el or
spin-Peierls).We show that these correlated spin systems made of hundreds of
coupled spin bear an overall spin S=1/2 and can be manipulated as a single
spin. This is clearly contrary to all known spin-qubits which are paramagnetic
centres, highly diluted to prevent decoherence. These results offer an
alternative approach for spin-qubits paving the way for the implementation of a
new type of quantum computer
Measuring Motional Dynamics of (CH) NH in the Perovskite-Like Metal--Organic Framework [(CH) NH][Zn(HCOO)]: The Value of Low-Frequency Electron Paramagnetic Resonance
Dimethylammonium zinc formate (DMAZnF) is the precursor for a large family of
multiferroics, materials which display co-existing magnetic and dielectric
ordering. However, the mechanism underlying these orderings remains unclear.
While it is generally believed that the dielectric transition is related to the
freezing of the order-disorder dynamics of the dimethylammonium (DMA+) cation,
no quantitative data on this motion are available. We surmise that this is due
to the fact that the timescale of this cationic motion is on the borderline of
the timescales of experimental techniques used in earlier reports. Using
multifrequency EPR, we find that the timescale of this motion is ~ 5 x 10 -9 s.
Thus, S-band (4 GHz) EPR spectroscopy is presented as the technique of choice
for studying these motional dynamics. This work highlights the value of the
lower-frequency end of EPR spectroscopy. The data are interpreted using DFT
calculations and provide direct evidence for the motional freezing model of the
ferroelectric transition in these metal-organic frameworks with the ABX3
perovskite-like architecture
Electron spin resonance in the =1/2 quasi-one-dimensional antiferromagnet with Dzyaloshinskii-Moriya interaction BaCuGeO
We have investigated the electron spin resonance (ESR) on single crystals of BaCuGeO at temperatures between 300 and 2 K and in a large frequency band, 9.6 -134 GHz, in order to test the predictions of a recent theory, proposed by Oshikawa and Affleck (OA), which describes the ESR in a =1/2 Heisenberg chain with the Dzyaloshinskii-Moriya interaction. We find, in particular, that the ESR linewidth, , displays a rich temperature behavior. As the temperature decreases from 170 K to 50 K, shows a rapid and linear decrease, . At low temperatures, below 50 K, acquires a strong dependence on the magnetic field orientation and for it shows a behavior which is due to an induced staggered field , according to OA's prediction
Quantum Coherence of Strongly Correlated Defects in Spin Chains
AbstractMost of qubit systems known to date are isolated paramagnetic centres in magnetically diluted samples since their dilution allows to considerably weaken the dipole-dipole inter-qubit interaction and thus to prevent the decoherence. Here we suggest an alternative approach for spin qubits which are built on spin S = 1/2 defects in magnetically concentrated strongly correlated systems - spin chains. The corresponding qubits are made of spin solitons resulting from local breaking of transitional symmetry associated with point-defects. We provide the first evidence for coherence and Rabi oscillations of spin solitons in isotropic Heisenberg chains, simple antiferromagnetic-Ńeel or spin-Peierls, proving that they can be manipulated as single spin S = 1/2. The entanglement of these many-body soliton states over macroscopic distances along chains gives rise to networks of coupled qubits which could easily be decoupled at will in extensions of this work
Ferromagnetic resonance and magnetic damping in C-doped Mn5Ge3
International audience2 X-band ferromagnetic resonance (FMR) was used to investigate static and dynamic magnetic properties of Mn5Ge3 and Carbon-doped Mn5Ge3 (C0.1 and C0.2) thin films grown on Ge(111). The temperature dependence of magnetic anisotropy shows an increased perpendicular magneto-crystalline contribution at low temperature with an in-plane easy axis due to the large shape contribution. We find that our samples show as small as 40Oe FMR linewidth (corresponding Gilbert damping α=0.005), for the out-of-plane direction, certifying of their very good structural quality. The perpendicular linewidth shows a minimum around 200K for all samples, which seems not correlated to the C-doping. The magnetic relaxation parameters have been determined and indicate as main extrinsic contribution the two-magnon scattering. A transition from six-fold to twofold plus fourth-fold in-plane anisotropy is observed in the FMR linewidth of Mn5Ge3C0.2 around 200K
Very low-temperature epitaxial growth of Mn5Ge3 and Mn5Ge3C0.2 films on Ge(111) using molecular beam epitaxy
International audienceC-doped Mn5Ge3 compound is ferromagnetic at temperature up to 430 K. Hence it is a potential spin injector into group-IV semiconductors. Segregation and diffusion of Mn at the Mn5Ge3 /Ge interface could severely hinder the efficiency of the spin injection. To avoid these two phenomena we investigate the growth of Mn5Ge3 and C-doped Mn5Ge3 films on Ge(111) substrates by molecular beam epitaxy at room-temperature. The reactive deposition epitaxy method is used to deposit these films. Reflection high energy electron diffraction, X-ray diffraction analysis, transmission electron microscopy and atomic force microscopy indicate that the crystalline quality is very high. Magnetic characterizations by superconducting quantum interference device and ferromagnetic resonance reinforce the structural analysis results on the thin films quality
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