104 research outputs found
Spin–glass magnetism in RFeTi2O7 (R=Lu and Tb) compounds
20th International Conference on Magnetism.The compounds RFeTi2O7 (R=Lu and Tb) crystallize at room temperature in centrosymmetric orthorhombic space group Pcnb. There are five non-equivalent positions of the iron ions: the two positions, Fe’ and Fe”, in the octahedron consisting of the Fe’ tetrahedron and Fe” five-vertex polyhedron and the three positions, Fe1, Fe2 and Fe3 in the mixed Fe-Ti octahedra [1]. The populations of the mixed Fe-Ti sites are different. The crystal structure features lead to atomic disorder in the distribution of the magnetic ions in this compound. From low temperature heat capacity, magnetization and frequency dependent ac susceptibility we conclude that both compounds undergo a spin glass transition at TSG=4.5 and 6 K for R =Lu and Tb, respectively. Since Lu is not magnetic, in RFeTi2O7 the spin glass behavior is caused by the disordered distribution of the magnetic Fe3+ ions in the different crystallographic positions. The substitution of the magnetic and highly anisotropic Tb ion instead of Lu increases TSG because of the additional Tb-Fe exchange interaction, while the critical exponent of the frequency dependence on temperature hardly varies. The spin glass behavior in these crystalline compounds is caused by the presence of competitive interactions that lead to frustration.The financial support of the Spanish MINECO MAT2011-23791, MAT2014-53921-R and Aragonese DGA-IMANA E34 projects is acknowledged.Peer Reviewe
Spin dynamics in copper metaborate studied by muon spin relaxation
Copper metaborate CuBO was studied by muon spin relaxation
measurements in order to clarify its static and dynamic magnetic properties.
The time spectra of muon spin depolarization suggest that the local fields at
the muon site contain both static and fluctuating components in all ordered
phases down to 0.3 K. In the weak ferromagnetic phase (20 K~~9.3 K), the
static component is dominant. On the other hand, upon cooling the fluctuating
component becomes dominant in the incommensurate helix phase (9.3K > T > 1.4K).
The dynamical fluctuations of the local fields persist down to 0.3K, where a
new incommensurate phase (T < 1.4K) is expected to appear. This result suggests
that spins fluctuate even at T \to 0. We propose two possible origins of the
remnant dynamical spin fluctuations: frustration of the exchange interactions
and the dynamic behavior of the soliton lattice
Conductivity, weak ferromagnetism and charge instability in single crystal
The temperature dependence of resistivity, magnetization and electron-spin
resonance of the single crystal were measured in temperature
range of . Magnetization hysteresis in applied magnetic field
up to 0.7 T at , irreversible temperature behavior of
magnetization and resistivity were found . The obtained data were explained in
terms of degenerate tight binding model using random phase approximation. The
contribution of holes in and bands of manganese ions to the
conductivity, optical absorbtion spectra and charge instability in were studied. Charge susceptibility maxima resulted from the competition of
the on-site Coulomb interaction between the holes in different orbitals and
small hybridization of sub-bands were calculated at .Comment: 6 pages, 12 figure
A single chain analysis of doped quasi one dimensional spin 1 compounds: paramagnetic versus spin 1/2 doping
We present a numerical study of single chain models of doped spin 1
compounds. We use low energy effective one-dimensional models for both the
cases of paramagnetic and spin-1/2 doping. In the case of paramagnetic doping,
the effective model is equivalent to the bond disordered spin-1/2 chain model
recently analyzed by means of real space renormalization group by Hyman and
Yang. By means of exact diagonalizations in the XX limit, we confirm the
stability of the Haldane phase for weak disorder. Above a critical amount of
disorder, the effective model flows to the so called random singlet fixed
point. In the case of spin-1/2 doping, we argue that the Haldane phase should
be destabilized even for weak disorder. This picture is not in contradiction
with existing experimental data. We also discuss the possible occurrence of
(unobserved) antiferromagnetically ordered phases.Comment: 13 pages, 7 included figure
Spin-Glass State in
Magnetic susceptibility, magnetization, specific heat and positive muon spin
relaxation (\musr) measurements have been used to characterize the magnetic
ground-state of the spinel compound . We observe a spin-glass
transition of the S=1/2 spins below characterized
by a cusp in the susceptibility curve which suppressed when a magnetic field is
applied. We show that the magnetization of depends on the
magnetic histo Well below , the muon signal resembles the dynamical
Kubo-Toyabe expression reflecting that the spin freezing process in results Gaussian distribution of the magnetic moments. By means of
Monte-Carlo simulati we obtain the relevant exchange integrals between the spins in this compound.Comment: 6 pages, 16 figure
Magnetic Excitations in quasi two-dimensional Spin-Peierls Systems
A study is presented of a two-dimensional frustrated and dimerized quantum
spin-system which models the effect of inter-chain coupling in a spin-Peierls
compound. Employing a bond-boson method to account for quantum disorder in the
ground state the elementary excitations are evaluated in terms of gapful
triplet modes. Results for the ground state energy and the spin gap are
discussed. The triplet dispersion is found to be in excellent agreement with
inelastic neutron scattering data in the dimerized phase of the spin-Peierls
compound CuGeO_3. Moreover, consistent with these neutron scattering
experiments, the low-temperature dynamic structure factor exhibits a
high-energy continuum split off from the elementary triplet mode.Comment: 8 pages, Revtex, 8 eps-figure
Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets
A phenomenological theory of magnetic states in noncentrosymmetric tetragonal
antiferromagnets is developed, which has to include homogeneous and
inhomogeneous terms (Lifshitz-invariants) derived from Dzyaloshinskii-Moriya
couplings. Magnetic properties of this class of antiferromagnets with low
crystal symmetry are discussed in relation to its first known members, the
recently detected compounds Ba2CuGe2O7 and K2V3O8. Crystallographic symmetry
and magnetic ordering in these systems allow the simultaneous occurrence of
chiral inhomogeneous magnetic structures and weak ferromagnetism. New types of
incommensurate magnetic structures are possible, namely, chiral helices with
rotation of staggered magnetization and oscillations of the total
magnetization. Field-induced reorientation transitions into modulated states
have been studied and corresponding phase diagrams are constructed. Structures
of magnetic defects (domain-walls and vortices) are discussed. In particular,
vortices, i.e. localized non-singular line defects, are stabilized by the
inhomogeneous Dzyaloshinskii-Moriya interactions in uniaxial noncentrosymmetric
antiferromagnets.Comment: 18 pages RevTeX4, 13 figure
Spin-Glass State in
Magnetic susceptibility, magnetization, specific heat and positive muon spin
relaxation (\musr) measurements have been used to characterize the magnetic
ground-state of the spinel compound . We observe a spin-glass
transition of the S=1/2 spins below characterized
by a cusp in the susceptibility curve which suppressed when a magnetic field is
applied. We show that the magnetization of depends on the
magnetic histo Well below , the muon signal resembles the dynamical
Kubo-Toyabe expression reflecting that the spin freezing process in results Gaussian distribution of the magnetic moments. By means of
Monte-Carlo simulati we obtain the relevant exchange integrals between the spins in this compound.Comment: 6 pages, 16 figure
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