205 research outputs found
Berezinskii-Kosterlitz-Thouless Type Scenario in Molecular Spin Liquid CrO
The spin relaxation in chromium spinel oxides CrO ( Mg,
Zn, Cd) is investigated in the paramagnetic regime by electron spin resonance
(ESR). The temperature dependence of the ESR linewidth indicates an
unconventional spin-relaxation behavior, similar to spin-spin relaxation in the
two-dimensional (2D) chromium-oxide triangular lattice antiferromagnets. The
data can be described in terms of a generalized Berezinskii-Kosterlitz-Thouless
(BKT) type scenario for 2D systems with additional internal symmetries. Based
on the characteristic exponents obtained from the evaluation of the ESR
linewidth, short-range order with a hidden internal symmetry is suggested.Comment: 7 pages, 4 figure
On the complexity of spinels: magnetic, electronic, and polar ground states
This review summarizes more than 100 years of research on spinel compounds,
mainly focusing on the progress in understanding their magnetic, electronic,
and polar properties during the last two decades. Many spinel compounds are
magnetic insulators or semiconductors; however, a number of spinel-type metals
exists including superconductors and some rare examples of d-derived
heavy-fermion compounds. In the early days, they gained importance as
ferrimagnetic or even ferromagnetic insulators with relatively high saturation
magnetization and high ordering temperatures, with magnetite being the first
magnetic mineral known to mankind. However, spinels played an outstanding role
in the development of concepts of magnetism, in testing and verifying the
fundamentals of magnetic exchange, in understanding orbital-ordering and
charge-ordering phenomena. In addition, the A- site as well as the B-site
cations in the spinel structure form lattices prone to strong frustration
effects resulting in exotic ground-state properties. In case the A-site cation
is Jahn-Teller active, additional entanglements of spin and orbital degrees of
freedom appear, which can give rise to a spin-orbital liquid or an orbital
glass state. The B-site cations form a pyrochlore lattice, one of the strongest
contenders of frustration in three dimensions. In addition, in spinels with
both cation lattices carrying magnetic moments, competing magnetic exchange
interactions become important, yielding ground states like the time-honoured
triangular Yafet-Kittel structure. Finally, yet importantly, there exists a
long-standing dispute about the possibility of a polar ground state in spinels,
despite their reported overall cubic symmetry. Indeed, over the years number of
multiferroic spinels were identified.Comment: 118 pages, 60 figure
Spin dynamics of the ordered phase of the frustrated antiferromagnet ZnCr2O4: a magnetic resonance study
We present an elaborate electron-spin resonance study of the low-energy dynamics and magnetization in the ordered phase of the frustrated spinel ZnCr2O4. We observe several resonance modes corresponding to different structural domains and found that the number of domains can be easily reduced by field-cooling the sample through the transition point. To describe the observed antiferromagnetic resonance spectra it is necessary to take into account an orthorhombic lattice distortion in addition to the earlier reported tetragonal distortion which both appear at the antiferromagnetic phase transition
Orbital Freezing in FeCr2S4 Studied by Dielectric Spectroscopy
Broadband dielectric spectroscopy has been performed on single-crystalline
FeCr2S4 revealing a transition into a low-temperature orbital glass phase and
on polycrystalline FeCr2S4 where long-range orbital order is established via a
cooperative Jahn-Teller transition. The freezing of the orbital moments is
revealed by a clear relaxational behavior of the dielectric permittivity, which
allows a unique characterization of the orbital glass transition. The orbital
relaxation dynamics continuously slows down over six decades in time, before at
the lowest temperatures the glass transition becomes suppressed by quantum
tunneling.Comment: 4 pages, 4 figure
Magnetic Excitations in the Multiferroic N\'eel-type Skyrmion Host GaVS
Broadband microwave spectroscopy has been performed on single-crystalline
GaVS, which exhibits a complex magnetic phase diagram including
cycloidal, N\'eel-type skyrmion lattice, as well as field-polarized
ferromagnetic phases below 13 K. At zero and small magnetic fields two
collective modes are found at 5 and 15 GHz, which are characteristic of the
cycloidal state in this easy-axis magnet. In finite fields, entering the
skyrmion lattice phase, the spectrum transforms into a multi-mode pattern with
absorption peaks near 4, 8, and 15 GHz. The spin excitation spectra in
GaVS and their field dependencies are found to be in close relation to
those observed in materials with Bloch-type skyrmions. Distinct differences
arise from the strong uniaxial magnetic anisotropy of GaV4S8 not present in
so-far known skyrmion hosts
Anisotropic Exchange in
We investigate the magnetic properties of the multiferroic quantum-spin
system LiCuO by electron spin resonance (ESR) measurements at - and
-band frequencies in a wide temperature range \,K). The observed anisotropies of the tensor and the ESR linewidth in
untwinned single crystals result from the crystal-electric field and from local
exchange geometries acting on the magnetic Cu ions in the zigzag-ladder
like structure of LiCuO. Supported by a microscopic analysis of the
exchange paths involved, we show that both the symmetric anisotropic exchange
interaction and the antisymmetric Dzyaloshinskii-Moriya interaction provide the
dominant spin-spin relaxation channels in this material.Comment: 10 pages, 10 Figure
Role of alkaline metal in the rare-earth triangular antiferromagnet KYbO
We report crystal structure and magnetic behavior of the triangular
antiferromagnet KYbO, the A-site substituted version of the quantum spin
liquid candidate NaYbO. The replacement of Na by K introduces an
anisotropic tensile strain with 1.6% in-plane and 12.1% out-of-plane lattice
expansion. Compared to NaYbO, both Curie-Weiss temperature and saturation
field are reduced by about 20% as the result of the increased Yb--O--Yb angles,
whereas the -tensor of Yb becomes isotropic with .
Field-dependent magnetization shows the plateau at 1/2 of the saturated value
and suggests the formation of the up-up-up-down field-induced order in the
triangular AYbO oxides (A = alkali metal), in contrast to the isostructural
selenides that exhibit the 1/3 plateau and the up-up-down field-induced order
Evidence for a Ru Kondo Lattice in LaCuRuO
Rare -electron derived heavy-fermion properties of the solid-solution
series LaCuRuTiO were studied for by
resistivity, susceptibility, specific-heat measurements, and magnetic-resonance
techniques. The pure ruthenate () is a heavy-fermion metal characterized
by a resistivity proportional to at low temperatures . The coherent
Kondo lattice formed by the localized Ru 4 electrons is screened by the
conduction electrons leading to strongly enhanced effective electron masses. By
increasing titanium substitution the Kondo lattice becomes diluted resulting in
single-ion Kondo properties like in the paradigm -based heavy-fermion
compound CeLaCuSi [M. Ocko {\em et al.}, Phys. Rev. B
\textbf{64}, 195106 (2001)]. In LaCuRuTiO the
heavy-fermion behavior finally breaks down on crossing the metal-to-insulator
transition close to .Comment: 9 pages, 8 figure
Magnetic and vibrational properties of the covalent chain antiferromagnet RbFeS2
Ternary rubidium-iron sulfide, RbFeS2, belongs to a family of quasi-one-dimensional compounds with the general chemical composition AFeCh2 (where A – K, Rb, Cs, Tl; Ch – S, Se). Understanding the magnetic properties of these compounds is a challenge. The controversy concerning the spin-state of the iron ion needs to be resolved to build the proper model of magnetism. Single crystals of RbFeS2 were grown and characterized by powder x-ray diffraction. QD MPMS-5 SQUID magnetometry was used to measure the magnetic susceptibility, and specific heat was measured utilizing QD PPMS-9 setup. Above the transition to three-dimensional antiferromagnetic order at the Néel temperature of TN = 188 K, the susceptibility exhibits unusual quasi-linear increase up to the highest measured temperature of 500 K. The specific heat was measured in the temperature range 1.8 – 300 K. Ab initio phonon dispersion and density-of-states calculations were performed by means of density functional theory (DFT), and the calculated lattice specific heat was subtracted from the measured one giving the magnetic contribution to the specific heat. Our results suggest that the features of the magnetic specific heat are general for the whole family of the covalent chain ternary iron chalcogenides of the AFeCh2 structure and indicate an intermediate S = 3/2 spin state of the iron ion
Synthesis, thermal stability and magnetic properties of an interpenetrated Mn(II) triazolate coordination framework
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