5,874 research outputs found
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
Determination of the zero-field magnetic structure of the helimagnet MnSi at low temperature
Below a temperature of approximately 29 K the manganese magnetic moments of
the cubic binary compound MnSi order to a long-range incommensurate helical
magnetic structure. Here, we quantitatively analyze a high-statistic zero-field
muon spin rotation spectrum recorded in the magnetically ordered phase of MnSi
by exploiting the result of representation theory as applied to the
determination of magnetic structures. Instead of a gradual rotation of the
magnetic moments when moving along a axis, we find that the angle of
rotation between the moments of certain subsequent planes is essentially
quenched. It is the magnetization of pairs of planes which rotates when moving
along a axis, thus preserving the overall helical structure.Comment: 10 pages, 4 figure
Magnetic order, spin waves and fluctuations in the triangular antiferromagnet La2Ca2MnO7
We report magnetic susceptibility, specific heat and muon spin relaxation
(muSR) experiments on the triangular antiferromagnet La2Ca2MnO7 which develops
a genuine two-dimensional, three-sublattice \sqrt{3} \times \sqrt{3} magnetic
order below T_N = 2.8 K. From the susceptibility and specific heat data an
estimate of the exchange interaction is derived. A value for the spin-wave gap
is obtained from the latter data. The analysis of a previously reported
inelastic neutron scattering study yields values for the exchange and spin-wave
gap compatible with the results obtained from macroscopic measurements. An
appreciable entropy is still missing at 10 K that may be ascribed to intense
short-range correlations. The critical paramagnetic fluctuations extend far
above T_N, and can be partly understood in terms of two-dimensional spin-wave
excitations. While no spontaneous muSR field is observed below T_N, persistent
spin dynamics is found. Short-range correlations are detected in this
temperature range. Their relation to a possible molecular spin substructure and
the observed exotic spin fluctuations is discussed.Comment: 9 pages, 6 figure
Understanding the SR spectra of MnSi without magnetic polarons
Transverse-field muon-spin rotation (SR) experiments were performed on a
single crystal sample of the non-centrosymmetric system MnSi. The observed
angular dependence of the muon precession frequencies matches perfectly the one
of the Mn-dipolar fields acting on the muons stopping at a 4a position of the
crystallographic structure. The data provide a precise determination of the
magnetic dipolar tensor. In addition, we have calculated the shape of the field
distribution expected below the magnetic transition temperature at the 4a
muon-site when no external magnetic field is applied. We show that this field
distribution is consistent with the one reported by zero-field SR studies.
Finally, we present ab initio calculations based on the density-functional
theory which confirm the position of the muon stopping site inferred from
transverse-field SR. In view of the presented evidence we conclude that
the SR response of MnSi can be perfectly and fully understood without
invoking a hypothetical magnetic polaron state.Comment: 10 pages, 12 figure
High pressure magnetic state of MnP probed by means of muon-spin rotation
We report a detailed SR study of the pressure evolution of the magnetic
order in the manganese based pnictide MnP, which has been recently found to
undergo a superconducting transition under pressure once the magnetic ground
state is suppressed. Using the muon as a volume sensitive local magnetic probe,
we identify a ferromagnetic state as well as two incommensurate helical states
(with propagation vectors aligned along the crystallographic and
directions, respectively) which transform into each other through first
order phase transitions as a function of pressure and temperature. Our data
appear to support that the magnetic state from which superconductivity develops
at higher pressures is an incommensurate helical phase.Comment: 11 pages, 9 figure
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Magnetic quantum critical point and superconductivity in UPt3 doped with Pd
Transverse-field muon spin relaxation measurements have been carried out on
the heavy-fermion superconductor UPt3 doped with small amounts of Pd. We find
that the critical Pd concentration for the emergence of the large-moment
antiferromagnetic phase is ~0.6 at.%Pd. At the same Pd content,
superconductivity is completely suppressed. The existence of a magnetic quantum
critical point in the phase diagram, which coincides with the critical point
for superconductivity, provides evidence for ferromagnetic spin-fluctuation
mediated odd-parity superconductivity, which competes with antiferromagnetic
order.Comment: 4 pages (includes 3 figures); postscript fil
Muon localization site in U(Pt,Pd)3
The angular and temperature (10-250 K) variation of the Knight shift of
single-crystalline U(Pt0.95Pd0.05)3 has been measured in transverse field
(B=0.6 T) mSR experiments. By analysing the temperature variation of the Knight
shift with a modified Curie-Weiss expression the muon localization site in this
hexagonal material is determined at (0,0,0).Comment: 12 pages (including 4 figures); postscript file; Proc. 8th Int. Conf.
on Muon Spin Rotation, Relaxation and Resonance (Aug.30-Sept.3, Les
Diablerets); 2nd version with minor correction
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