10 research outputs found
Ga substitution as an effective variation of Mn-Tb coupling in multiferroic TbMnO3
Ga for Mn substitution in multiferroic TbMnO has been performed in
order to study the influence of Mn-magnetic ordering on the Tb-magnetic
sublattice. Complete characterization of TbMnGaO ( = 0,
0.04, 0.1) samples, including magnetization, impedance spectroscopy, and x-ray
resonant scattering and neutron diffraction on powder and single crystals has
been carried out. We found that keeping the same crystal structure for all
compositions, Ga for Mn substitution leads to the linear decrease of and , reflecting the reduction of the exchange
interactions strength and the change of the Mn-O-Mn bond
angles. At the same time, a strong suppression of both the induced and the
separate Tb-magnetic ordering has been observed. This behavior unambiguously
prove that the exchange fields have a strong influence on the
Tb-magnetic ordering in the full temperature range below
and actually stabilize the Tb-magnetic ground state.Comment: 9 pages, 8 figure
Field-induced bound-state condensation and spin-nematic phase in SrCu(BO) revealed by neutron scattering up to 25.9 T
Bose-Einstein condensation (BEC) underpins exotic forms of order ranging from
superconductivity to superfluid 4 He. In quantum magnetic materials, ordered
phases induced by an applied magnetic field can be described as the BEC of
magnon excitations. With sufficiently strong magnetic frustration, exemplified
by the system SrCu(BO) , no clear magnon BEC is observed and the
complex spectrum of multi-magnon bound states may allow a different type of
condensation, but the high fields required to probe this physics have remained
a barrier to detailed investigation. Here we exploit the first purpose-built
high-field neutron scattering facility to measure the spin excitations of
SrCu(BO) up to 25.9 T and use cylinder matrix-product-states (MPS)
calculations to reproduce the experimental spectra with high accuracy. Multiple
unconventional features point to a condensation of bound states into a
spin-nematic phase, including the gradients of the one-magnon branches, the
presence of many novel composite two- and three-triplon excitations and the
persistence of a one-magnon spin gap. This gap reflects a direct analogy with
superconductivity, suggesting that the spin-nematic phase in
SrCu(BO) is best understood as a condensate of bosonic Cooper
pairs. Our results underline the wealth of unconventional states yet to be
found in frustrated quantum magnetic materials under extreme conditions
Magnetic structures and magnetovolume anomalies in R2Fe17 intermetallic compounds.
Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi
Analysis of time-of-flight small-angle neutron scattering data on mesoscopic crystals such as magnetic vortex lattices
Bragg diffracted intensities and q values for crystalline structures with long repeat distances may be obtained by small-angle neutron scattering (SANS) investigations. An account is given of the methods, advantages and disadvantages of obtaining such data by the multichromatic time-of-flight method, compared with the more traditional quasi-monochromatic SANS method. This is illustrated with data obtained from high-magnetic-field measurements on magnetic vortex line lattices in superconductors on the former HFM/EXED instrument at Helmholtz-Zentrum Berlin. The methods have application to other mesoscopic crystalline structures investigated by SANS instruments at pulsed sources
Magnetic order, hysteresis, and phase coexistence in magnetoelectric LiCoPO4
The magnetic phase diagram of magnetoelectric LiCoPO is established using
neutron diffraction and magnetometry in fields up to 25.9T applied along the
crystallographic -axis. For fields greater than 11.9T the magnetic unit cell
triples in size with propagation vector Q = (0, 1/3, 0). A magnetized elliptic
cycloid is formed with spins in the -plane and the major axis oriented
along . Such a structure allows for the magnetoelectric effect with an
electric polarization along induced by magnetic fields applied along .
Intriguingly, additional ordering vectors Q (0, 1/4, 0) and Q
(0, 1/2, 0) appear for increasing fields in the hysteresis region
below the transition field. Traces of this behavior are also observed in the
magnetization. A simple model based on a mean-field approach is proposed to
explain these additional ordering vectors. In the field interval 20.5-21.0T,
the propagation vector Q = (0, 1/3, 0) remains but the spins orient differently
compared to the cycloid phase. Above 21.0T and up until saturation a
commensurate magnetic structure exists with a ferromagnetic component along
and an antiferromagnetic component along
Dispersions of many-body Bethe strings
Complex bound states of magnetic excitations, known as Bethe strings, were predicted almost a century ago to exist in one-dimensional quantum magnets(1). The dispersions of the string states have so far remained the subject of intense theoretical studies(2-7). Here, by performing neutron scattering experiments on the one-dimensional Heisenberg-Ising antiferromagnet SrCo2V2O8 in high longitudinal magnetic fields, we reveal in detail the dispersion relations of the string states over the full Brillouin zone, as well as their magnetic field dependencies. Furthermore, the characteristic energy, the scattering intensity and linewidth of the observed string states exhibit excellent agreement with our precise Bethe-ansatz calculations. Our results establish the important role of string states in the quantum spin dynamics of one-dimensional systems, and will invoke studies of their dynamical properties in more general many-body systems. In one-dimensional quantum magnets, complex bound states of magnetic excitations known as Bethe strings have long been predicted. Now, a detailed neutron scattering study of SrCo2V2O8 reveals their magnetic-field-dependent dispersion relation