169 research outputs found
Relaxation in the 3D ordered CoTAC spin chain by quantum nucleation of 0D domain walls
We have shown that resonant quantum tunnelling of the magnetisation (QTM),
until now observed only in 0D cluster systems (SMMs), occurs in the molecular
Ising spin chain, CoTAC ([(CH_3)_3NH]CoCl_3 - 2H_2O) which orders as a canted
3D-antiferromagnet at T_C=4.15 K. This effect was observed around a resonant
like field value of 1025 Oe. We present here measurements of the relaxation of
the magnetisation as a function of time, from the zero field cooled (ZFC)
antiferromagnet state and from the saturated ferromagnet state. We show that,
at the resonant field, the relaxation from the saturated state occurs in a
complicated process, whereas, surprisingly, in the case of the ZFC state, the
relaxation is exponential.Comment: 4 pages, 5 figures, LT25 proceeding
Updating the phase diagram of the archetypal frustrated magnet Gd3Ga5O12
The applied magnetic field and temperature phase diagram of the archetypal
frustrated magnet, Gd3Ga5O12, has been reinvestigated using single crystal
magnetometry and polarised neutron diffraction. The updated phase diagram is
substantially more complicated than previously reported and can be understood
in terms of competing interactions with loops of spins, trimers and decagons,
in addition to competition and interplay between antiferromagnetic,
incommensurate and ferromagnetic order. Several additional distinct phase
boundaries are presented. The phase diagram centers around a multiphase
convergence to a single point at 0.9 T and ~ 0.35 K, below which, in
temperature, a very narrow magnetically disordered region exists. These data
illustrate the richness and diversity that arises from frustrated exchange on
the 3 dimensional hyperkagome lattice
Candidate Quantum Spin Liquid in the Ce\textsuperscript{3+} Pyrochlore Stannate CeSnO
We report the low temperature magnetic properties of CeSnO, a
rare-earth pyrochlore. Our susceptibility and magnetization measurements show
that due to the thermal isolation of a Kramers doublet ground state,
CeSnO has Ising-like magnetic moments of
. The magnetic moments are confined to the local trigonal axes,
as in a spin ice, but the exchange interactions are antiferromagnetic. Below 1
K the system enters a regime with antiferromagnetic correlations. In contrast
to predictions for classical -Ising spins on the
pyrochlore lattice, there is no sign of long-range ordering down to 0.02 K. Our
results suggest that CeSnO features an antiferromagnetic liquid
ground state with strong quantum fluctuations.Comment: 6 pages, 4 figure
Palmer-Chalker correlations in the XY pyrochlore antiferromagnet Er2Sn2O7
\ersn\, is considered, together with \erti, as a realization of the XY
antiferromagnet on the pyrochlore lattice. We present magnetization
measurements confirming that \ersn\, does not order down to 100 mK but exhibits
a freezing below 200 mK. Our neutron scattering experiments evidence the strong
XY character of the \er moment and point out the existence of short range
correlations in which the magnetic moments are in peculiar configurations, the
Palmer-Chalker states, predicted theoretically for an XY pyrochlore
antiferromagnet with dipolar interactions. Our estimation of the \ersn\,
parameters confirm the role of the latter interactions on top of relatively
weak and isotropic exchange couplings
Intrinsic avalanches and collective phenomena in a Mn(II)-free radical ferrimagnetic chain
Magnetic hysteresis loops below 300 mK on single crystals of the Mn(II) -
nitronyl nitroxide free radical chain (Mn(hfac)_2({\it R})-3MLNN) present
abrupt reversals of the magnetization, or avalanches. We show that, below 200
mK, the avalanches occur at a constant field, independent of the sample and so
propose that this avalanche field is an intrinsic property. We compare this
field to the energy barrier existing in the sample and conclude that the
avalanches are provoked by multiple nucleation of domain-walls along the
chains. The different avalanche field observed in the zero field cooled
magnetization curves suggests that the avalanche mechanisms are related to the
competition between ferromagnetic and antiferromagnetic order in this compound.Comment: 9 pages, 7 fig, to be published in Phys. Rev.
Magnetic structure and dynamics of a strongly one-dimensional cobalt metal-organic framework
We investigate the magnetism of the
Co(OH)(CHO) metal-organic framework which
displays complex inorganic chains separated from each other by distances of 1
to 2 nm, and which orders at ~5.4 K. The zero-field magnetic structure is
determined using neutron powder diffraction: it is mainly antiferromagnetic but
posseses a ferromagnetic component along the -axis. This magnetic
structure persists in presence of a magnetic field. Ac susceptibility
measurements confirm the existence of a single thermally activated regime over
7 decades in frequency () whereas time-dependent relaxation
of the magnetization after saturation in an external field leads to a two times
smaller energy barrier. These experiments probe the slow dynamics of domain
walls within the chains: we propose that the ac measurements are sensitive to
the motion of existing domain walls within the chains, while the magnetization
measurements are governed by the creation of domain walls.Comment: 12 pages, 14 figure
Low-temperature magnetization in geometrically frustrated Tb2Ti2O7
The nature of the low temperature ground state of the pyrochlore compound
Tb2Ti2O7 remains a puzzling issue. Dynamic fluctuations and short-range
correlations persist down to 50 mK, as evidenced by microscopic probes. In
parallel, magnetization measurements show irreversibilities and glassy behavior
below 200 mK. We have performed magnetization and AC susceptibility
measurements on four single crystals down to 57 mK. We did not observe a clear
plateau in the magnetization as a function of field along the [111] direction,
as suggested by the quantum spin ice model. In addition to a freezing around
200 mK, slow dynamics are observed in the AC susceptibility up to 4 K. The
overall frequency dependence cannot be described by a canonical spin-glass
behavior.Comment: 5 pages, 4 figures + Supp. Mat (3 pages, 5 figures
Evidence for unidimensional low-energy excitations as the origin of persistent spin dynamics in geometrically frustrated magnets
We report specific heat, magnetic, and muon spin relaxation measurements
performed on a polycrystalline sample of the normal spinel CdHo2S4. The
rare-earth ions sit on a lattice of corner-sharing regular tetrahedra as in
pyrochlore compounds. Magnetic ordering is detected at Tc ~ 0.87 K. From
spin-lattice relaxation rate measurements on both sides of Tc we uncover
similar magnetic excitation modes driving the so-called persistent spin
dynamics at T < Tc. Unidimensional excitations are argued to be at its origin.
Often observed spin loop structures are suggested to support these excitations.
The possibility of a generic mechanism for their existence is discussed.Comment: 7 pages, 8 figure
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