| 1. |
-
- 2019
-
Tidskriftsartikel (refereegranskat)
|
|
| 2. |
- Gao, S., et al.
(författare)
-
Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2 O4
- 2018
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 97:13
-
Tidskriftsartikel (refereegranskat)abstract
- In spinels ACr2O4(A=Mg, Zn), realization of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition at TN=12.5 K. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberg et al. [Pow. Diff. 17, 230 (2002)PODIE20885-715610.1154/1.1479738], while other features depend on sample or cooling protocol. A complex, partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectors k1=(12120),k2=(1012) appear. The ordered moment reaches 1.94(3) μB/Cr3+ for k1 and 2.08(3) μB/Cr3+ for k2, if equal amount of the k1 and k2 phases is assumed. The magnetic arrangements have the dominant components along the [110] and [1-10] diagonals and a smaller c component. We use inelastic neutron scattering to investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. The distinctive fingerprint of clusterlike excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.
|
|
| 3. |
- Kalvius, G. M., et al.
(författare)
-
Magnetism of Pd1-xNix alloys near the critical concentration for ferromagnetism
- 2014
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:6, s. 064418-
-
Tidskriftsartikel (refereegranskat)abstract
- We report results of a muon spin rotation and relaxation (mu SR) study of dilute Pd1-xNix alloys, with emphasis on Ni concentrations x = 0.0243 and 0.025. These are close to the critical value x(cr) for the onset of ferromagnetic long-range order (LRO), which is a candidate for a quantum critical point. Additional control data were taken for pure nonmagnetic Pd, and for an alloy where ferromagnetism is well established (x = 0.05). The 2.43 and 2.5 at.% Ni alloys exhibit similar mu SR properties. Both samples are fully magnetic, with average zero-temperature muon local fields < B-loc(T = 0)> = 2.0 and 3.8 mT and Curie temperatures T-C = 1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively. The temperature dependence of < B-loc > suggests ordering of Ni spin clusters rather than isolated spins. Just above T-C, the temperature where LRO vanishes, a two-phase region is found with coexisting separate volume fractions of quasistatic short-range order (SRO) and paramagnetism. The SRO fraction decreases to zero with increasing temperature a few kelvin above T-C. This mixture of SRO and paramagnetism is consistent with the notion of an inhomogeneous alloy with Ni clustering. The measured values of T-C extrapolate to x(cr) = 0.0236 +/- 0.0027. The dynamic muon spin relaxation in the vicinity of T-C differs for the two samples: a relaxation-rate maximum at T-C is observed for x = 0.0243, reminiscent of critical slowing down, whereas for x = 0.025 no dynamic relaxation is observed within the mu SR time window. The data suggest a mean-field-like transition in this alloy.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Eremina, R. M., et al.
(författare)
-
Magnetization and specific heat of the dimer system CuTe(2)O(5)
- 2011
-
Ingår i: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 84:3, s. 391-395
-
Tidskriftsartikel (refereegranskat)abstract
- We report on magnetization and specific heat measurements on single-crystalline CuTe(2)O(5). The experimental data are directly compared to theoretical results for two different spin structures, namely an alternating spin-chain and a two-dimensional (2D) coupled dimer model, obtained by Das et al. [Phys. Rev. B 77, 224437 (2008)]. While the analysis of the specific heat does not allow to distinguish between the two models, the magnetization data is in good agreement with the 2D coupled dimer model.
|
|
| 7. |
- Kalvius, G. M., et al.
(författare)
-
Spin-Lattice Instability in the Chromium Sulfur Spinel Fe0.5Cu0.5Cr2S4
- 2008
-
Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 20:25, s. 252204-
-
Tidskriftsartikel (refereegranskat)abstract
- Zero field mu SR spectroscopy was applied to a polycrystalline sample of the ferrimagnetic sulfur spinel Fe0.5Cu0.5Cr2S4 between 5 and 315 K. The temperature dependence of the interstitial magnetic field B-mu as well as the transverse and longitudinal relaxation rates were deduced. At around 100 K, the temperature dependence of the interstitial field exhibits a strong deviation from the expected Brillouin-like behavior together with a maximum of the transverse relaxation rate. These features are characteristic for a spin reorientation transition. This instability of the ferrimagnetic spin-lattice has not been reported previously. Fe-57 Mossbauer data from the same sample show no irregularity in the temperature dependence of the Fe hyperfine field which could indicate that the spin reorientation involves primarily the Cr sublattice. Above and below the spin reorientation regime, disorder in the spin-lattice is sizable, but not excessive. At low temperatures, the spins are essentially static, spin dynamics sets in above the reorientation range. The mu SR data are also complemented by new susceptibility and magnetization data taken on similar material.
|
|
| 8. |
- Sherman, A, et al.
(författare)
-
Dielectric properties of C-70-solvate crystals grown from a benzene solution
- 1998
-
Ingår i: JOURNAL OF PHYSICAL CHEMISTRY B. - : AMER CHEMICAL SOC. ; 102:39
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- C-70 crystals with size up to 3 x 3 x 0.2 mm were grown from benzene solution. The real and imaginary parts of the complex conductivity of this crystals were studied in the frequency range 20 Hz-1 MHz and the temperature range from 10 K to the room temper
|
|
| 9. |
|
|
| 10. |
|
|
