5,813 research outputs found
Magnetoelectric properties of 500 nm Cr2O3 films
The linear magnetoelectric effect was measured in 500 nm Cr2O3 films grown by
rf sputtering on Al2O3 substrates between top and bottom thin film Pt
electrodes. Magnetoelectric susceptibility was measured directly by applying an
AC electric field and measuring the induced AC magnetic moment using
superconducting quantum interference device magnetometry. A linear dependence
of the induced AC magnetic moment on the AC electric field amplitude was found.
The temperature dependence of the magnetoelectric susceptibility agreed
qualitatively and quantitatively with prior measurements of bulk single
crystals, but the characteristic temperatures of the film were lower than those
of single crystals. It was also possible to reverse the sign of the
magnetoelectric susceptibility by reversing the sign of the magnetic field
applied during cooling through the N\'eel temperature. A competition between
total magnetoelectric and Zeeman energies is proposed to explain the difference
between film and bulk Cr2O3 regarding the cooling field dependence of the
magnetoelectric effect.Comment: accepted at Physical Review
Ac conductivity and dielectric properties of CuFe1−xCrxO2 : Mg delafossite
The electrical and dielectric properties of CuFe(1−x)Cr(x)O(2) (0 ≤ x ≤ 1) powders, doped with 3% of Mg and prepared by solid-state reaction, were studied by broadband dielectric spectroscopy in the temperature range from −100 to 150 °C. The frequency-dependent electrical and dielectric data have been discussed in the framework of a power law conductivity and complex impedance and dielectric modulus. At room temperature, the ac conductivity behaviour is characteristic of the charge transport in CuFe1−xCrxO2 powders. The substitution of Fe3+ by Cr3+ results in an increase in dc conductivity and a decrease in the Cu+–Cu+ distance. Dc conductivity, characteristic onset frequency and Havriliak–Negami characteristics relaxation times are thermally activated above −40 °C for x = 0.835. The associated activation energies obtained from dc and ac conductivity and from impedance and modulus losses are similar and show that CuFe1−xCrxO2 delafossite powders satisfy the BNN relation. Dc and ac conductivities have the same transport mechanism, namely thermally activated nearest neighbour hopping and tunnelling hopping above and below −40 °C, respectively
Renormalization group approach to vibrational energy transfer in protein
Renormalization group method is applied to the study of vibrational energy
transfer in protein molecule. An effective Lagrangian and associated equations
of motion to describe the resonant energy transfer are analyzed in terms of the
first-order perturbative renormalization group theory that has been developed
as a unified tool for global asymptotic analysis. After the elimination of
singular terms associated with the Fermi resonance, amplitude equations to
describe the slow dynamics of vibrational energy transfer are derived, which
recover the result obtained by a technique developed in nonlinear optics [S.J.
Lade, Y.S. Kivshar, Phys. Lett. A 372 (2008) 1077].Comment: 11 page
Spin dyanamics of traianglular lattice antiferromagnet CuFeO2: Crossover from spin-liquid to paramagnetic phase
RF amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance
The radio-frequency (RF) voltage amplification property of a tunnel
magnetoresistance device driven by an RF external-magnetic-field-induced
ferromagnetic resonance was studied. The proposed device consists of a magnetic
tunnel junction (MTJ) and an electrically isolated coplanar waveguide. The
input RF voltage applied to the waveguide can excite the resonant dynamics in
the free layer magnetization, leading to the generation of an output RF voltage
under a DC bias current. The dependences of the RF voltage gain on the static
external magnetic field strength and angle were systematically investigated.
The design principles for the enhancement of the gain factor are also
discussed.Comment: 12 pages, 3 figure
Two dimensionality in quasi one-dimensional cobalt oxides
By means of muon spin rotation and relaxation (SR) techniques, we have
investigated the magnetism of quasi one-dimensional (1D) cobalt oxides
CoO (=Ca, Sr and Ba, =1, 2, 3, 5 and
), in which the 1D CoO chain is surrounded by six equally spaced
chains forming a triangular lattice in the -plane, using polycrystalline
samples, from room temperature down to 1.8 K. For the compounds with =1 - 5,
transverse field SR experiments showed the existence of a magnetic
transition below 100 K. The onset temperature of the transition () was found to decrease with ; from 100 K for =1 to 60 K for
=5. A damped muon spin oscillation was observed only in the sample with
=1 (CaCoO), whereas only a fast relaxation obtained even at 1.8
K in the other three samples. In combination with the results of susceptibility
measurements, this indicates that a two-dimensional short-range
antiferromagnetic (AF) order appears below for all
compounds with =1 - 5; but quasi-static long-range AF order formed only in
CaCoO, below 25 K. For BaCoO (=), as decreased
from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF
transition occurred at 15 K.Comment: 12 pages, 14 figures, and 2 table
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