91 research outputs found
Dzyaloshinskii-Moriya interaction and spin re-orientation transition in the frustrated kagome lattice antiferromagnet
Magnetization, specific heat, and neutron scattering measurements were
performed to study a magnetic transition in jarosite, a spin-5/2 kagome lattice
antiferromagnet. When a magnetic field is applied perpendicular to the kagome
plane, magnetizations in the ordered state show a sudden increase at a critical
field H_c, indicative of the transition from antiferromagnetic to ferromagnetic
states. This sudden increase arises as the spins on alternate kagome planes
rotate 180 degrees to ferromagnetically align the canted moments along the
field direction. The canted moment on a single kagome plane is a result of the
Dzyaloshinskii-Moriya interaction. For H < H_c, the weak ferromagnetic
interlayer coupling forces the spins to align in such an arrangement that the
canted components on any two adjacent layers are equal and opposite, yielding a
zero net magnetic moment. For H > H_c, the Zeeman energy overcomes the
interlayer coupling causing the spins on the alternate layers to rotate,
aligning the canted moments along the field direction. Neutron scattering
measurements provide the first direct evidence of this 180-degree spin rotation
at the transition.Comment: 13 pages, 15 figure
Spin Dynamics of the Spin-1/2 Kagome Lattice Antiferromagnet ZnCu_3(OH)_6Cl_2
We have performed thermodynamic and neutron scattering measurements on the
S=1/2 kagome lattice antiferromagnet Zn Cu_3 (OH)_6 Cl_2. The susceptibility
indicates a Curie-Weiss temperature of ~ -300 K; however, no magnetic order is
observed down to 50 mK. Inelastic neutron scattering reveals a spectrum of low
energy spin excitations with no observable gap down to 0.1 meV. The specific
heat at low-T follows a power law with exponent less than or equal to 1. These
results suggest that an unusual spin-liquid state with essentially gapless
excitations is realized in this kagome lattice system.Comment: 4 pages, 3 figures; v2: Updates to authors list and references; v3:
Updated version; v4: Published versio
Magnetic excitations in a new anisotropic Kagom\'{e} antiferromagnet
The Nd-langasite compound contains planes of magnetic Nd3+ ions on a lattice
topologically equivalent to a kagom\'{e} net. The magnetic susceptibility does
not reveal any signature of long-range ordering down to 2 K but rather a
correlated paramagnetism with significant antiferromagnetic interactions
between the Nd and a single-ion anisotropy due to crystal field effect.
Inelastic neutron scattering on Nd-langasite powder and single-crystal allowed
to probe its very peculiar low temperature dynamical magnetic correlations.
They present unusual dispersive features and are broadly localized in
wave-vector Q revealing a structure factor associated to characteristics short
range-correlations between the magnetic atoms. From comparison with theoretical
calculations, these results are interpreted as a possible experimental
observation of a spin liquid state in an anisotropic kagom\'{e}
antiferromagnet.Comment: to appear in Physica
Spin chirality on a two-dimensional frustrated lattice
The collective behavior of interacting magnetic moments can be strongly
influenced by the topology of the underlying lattice. In geometrically
frustrated spin systems, interesting chiral correlations may develop that are
related to the spin arrangement on triangular plaquettes. We report a study of
the spin chirality on a two-dimensional geometrically frustrated lattice. Our
new chemical synthesis methods allow us to produce large single crystal samples
of KFe3(OH)6(SO4)2, an ideal Kagome lattice antiferromagnet. Combined
thermodynamic and neutron scattering measurements reveal that the phase
transition to the ordered ground-state is unusual. At low temperatures,
application of a magnetic field induces a transition between states with
different non-trivial spin-textures.Comment: 7 pages, 4 figure
Toward Perfection: Kapellasite, Cu3Zn(OH)6Cl2, a New Model S = 1/2 Kagome Antiferromagnet
The search for the resonating valence bond (RVB) state continues to underpin
many areas of condensed matter research. The RVB is made from the dimerisation
of spins on different sites into fluctuating singlets, and was proposed by
Anderson to be the reference state from which the transition to BCS
superconductivity occurs. Little is known about the state experimentally, due
to the scarcity of model materials. Theoretical work has put forward the S =
1/2 kagome antiferromagnet (KAFM) as a good candidate for the realization of
the RVB state. In this paper we introduce a new model system, the S = 1/2 KAFM
Kapellasite, Cu3Zn(OH)6Cl2. We show that its crystal structure is a good
approximation to a 2-dimensional kagome antiferromagnet and that susceptibility
data indicate a collapse of the magnetic moment below T = 25 K that is
compatible with the spins condensing into the non-magnetic RVB state.Comment: Communication, 3 pages, 3 figure
Slow Relaxation of Spin Structure in Exotic Ferromagnetic Phase of Ising-like Heisenberg Kagome Antiferromagnets
In the corner-sharing lattice, magnetic frustration causes macroscopic
degeneracy in the ground state, which prevents systems from ordering. However,
if the ensemble of the degenerate configuration has some global structure, the
system can have a symmetry breaking phenomenon and thus posses a finite
temperature phase transition. As a typical example of such cases, the magnetic
phase transition of the Ising-like Heisenberg antiferromagnetic model on the
kagome lattice has been studied. There, a phase transition of the
two-dimensional ferromagnetic Ising universality class occurs accompanying with
the uniform spontaneous magnetization. Because of the macroscopic degeneracy in
the ordered phase, the system is found to show an entropy-driven ordering
process, which is quantitatively characterized by the number of ``weathervane
loop''. We investigate this novel type of slow relaxation in regularly
frustrated system.Comment: 4 pages, 6 figure
Recommended from our members
Co3(SO4)3(OH)2[enH2]: a newS= 3/2 Kagome-type layered sulfate with a unique connectivity
The Kagome lattice, comprising a two-dimensional array of corner-sharing equilateral triangles, is central to the exploration of magnetic frustration. In such a lattice, antiferromagnetic coupling between ions in triangular plaquettes prevents all of the exchange interactions being simultaneously satisfied and a variety of novel magnetic ground states may result at low temperature. Experimental realization of a Kagome lattice remains difficult. The jarosite family of materials of nominal composition AM3(SO4)2(OH)6 (A = monovalent cation; M= Fe3+, Cr3+), offers perhaps one of the most promising manifestations of the phenomenon of magnetic frustration in two dimensions. The magnetic properties of jarosites are however extremely sensitive to the degree of coverage of magnetic sites. Consequently, there is considerable interest in the use of soft chemical techniques for the design and synthesis of novel materials in which to explore the effects of spin, degree of site coverage and connectivity on magnetic frustration
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
Biological Sex, Sex-Role Identity, and the Spectrum of Computing Orientations: A Re-Appraisal at the End of the 90s
Internet: a negatividade do discurso da mÃdia versus a positividade da experiência pessoal. À qual dar crédito?
- …