Antiferromagnetic ordering in superconducting YBa2Cu3O6.5

Commensurate antiferromagnetic ordering has been observed in the superconducting high- Tc cuprate YBa2Cu3O6.5 ( Tc = 55 K) by polarized and unpolarized elastic neutron scattering. The magnetic peak intensity exhibits a marked enhancement at Tc. Zero-field muon-spin-resonance experiments demonstrate that the staggered magnetization is not truly static but fluctuates on a nanosecond time scale. These results point towards an unusual spin density wave state coexisting with superconductivity.     

Antiferromagnetic ordering and metamagnetism in PrCuSi

A variety of physical properties measured on the hexagonal rare-earth intermetallic compound PrCuSi are presented. We provide compelling evidence for antiferromagnetic ordering at T_N = 5.1 K in this compound, in contrast to the former claim of ferromagnetic ordering at 14 K. The antiferromagnetic order is, however, found to be unstable in applied magnetic fields, becoming ferromagnetic beyond a metamagnetic transition at a field of 0.7 T at 2 K. It is argued that the magnetism in PrCuSi has the ingredients of a tricritical phase transition at the intersection of paramagnetism, ferromagnetism, and antiferromagnetism.     

Antiferromagnetic ordering in the ytterbium aluminum perovskite YbAlO3

The antiferromagnetic ordering in YbAlO₃ at low temperatures has been studied. Susceptibility measurements are in agreement with certain features of a quasi one-dimensional Ising system. Neutron diffraction below 0.8 K suggests a structure of the type A_xG_y. The spontaneous magnetic moment at 100 mK compares well with the value from the ground state doublet and is in disagreement with Mössbauer results.     

Antiferromagnetic ordering in REM cobaltite GdCoO<Subscript>3</Subscript>

Temperature and magnetic-field dependences of the static magnetization of polycrystalline cobaltite GdCoO₃ have been measured. The magnetic properties of the GdCoO₃ sample have been studied in the paramagnetic and antiferromagnetic states. The magnetic phase diagram has been constructed. The exchange field between the Gd-Gd sublattices and the anisotropy field have been estimated.     

Antiferromagnetic ordering in terbium dihydride. Low temperature heat capacity studies

The specific heat of terbium dihydride, TbH_2.01, was measured in the temperature range from 4–200 K. An extremely sharp λ-type specific heat anomaly due to an antiferromagnetic transition has been found at T_N = 16.06 ± 0.01 K.     

Antiferromagnetic Resonance in LaMnO3

The external magnetic field and temperature dependencies of the magnetic structure and antiferromagnetic resonance frequencies in LaMnO₃ are studied. A recently developed model which includes orbitally dependent superexchange and single-ion anisotropy interactions is used. The temperature dependence is described in the mean-field approximation in good agreement with experiments. H–T phase diagrams in the main field directions (a, b, c) are drawn. The problem of the origin of weak noncollinearity of Mn³⁺ spins is solved in our work. Also an optimal method for obtaining an expression of the magnetic free energy is represented. Authors' address: Alexey A. Mozhegorov, Physics Department, Urals State University, Lenin ulitsa 51, Yekaterinburg 620083, Russian Federation     

Antiferromagnetic ordering in magnetic ionic liquid Emim[FeCl4]

The magnetic ionic liquids (MILs) are considered to open up a wide range of applications because of their magnetic and electrochromic switching. Until recently almost all magnetic ionic liquids containing tetrachloroferrate ion FeCl₄⁻ evidenced a paramagnetic temperature dependence of the magnetic susceptibility, with only small deviations from the Curie law at low temperatures. However, 1-ethyl-3-methylimidazolium tetrachloroferrate, Emim[FeCl₄], clearly exhibits a long-range antiferromagnetic ordering below the Neel temperature T_N≈3.8 K. In addition, the shape of the magnetic ordering depends on the cooling speed, indicating that the magnetic coupling could be modified.     

Antiferromagnetic stripe ordering at the tetragonal-orthorhombic transition in LnOFeAs probed by X-ray absorption spectroscopy

Measurements of the Fe K-edge X-ray absorption near edge (XANES) spectra of LnOFeAs high T_c superconductors exhibit small but measurable changes across the tetragonal to orthorhombic phase structural phase transition. Calculations, based on the local structure centered at the Fe site obtained by crystallographic investigations, reproduce the observed changes in the spectra under the change of the crystal structure, indicating variations in the Fe local unoccupied electronic states. Calculated Fe density of states including stripe spin ordering in the orthorhombic phase show significant modifications with respect to Fe 3d density of states in the tetragonal phase or the density of states in the orthorhombic phase calculated ignoring spin ordering. This implies that the striped spin ordering in the orthorhombic phase is necessary to describe its electronic properties not only in the ground state but also for excited states above the Fermi energy.     

Orbital ordering in CuGeO3

The combined effect of the ligand crystal field and the exchange interaction on the Cu²⁺ cation in CuGeO₃ is examined. It is shown that, if the magnitude of the exchange interaction exceeds the splitting of the energy levels of the and d _xy orbitals, then an alternate filling of the d orbitals along a chain (orbital ordering) is possible. This effect creates an antiferromagnetic interaction between Cu²⁺ pairs in 90° exchange and a doubling of the lattice period. A Jahn-Teller pseudoeffect causes singletization of the ground state of the antiferromagnetic chain of Cu²⁺ spins. Fiz. Tverd. Tela (St. Petersburg) 40, 1686–1692 (September 1998)     

The Orientation of the Antiferromagnetic Order in FePS3

Hyperfine Interactions - Mössbauer spectroscopy was performed on FePS3. Magnetic moments of a single crystal were found to be parallel to the z-axis at temperatures below 96 K. The internal...     

Antiferromagnetic spin dynamics in exchanged-coupled Fe/GdFeO3 heterostructure

We investigate the ultrafast spin dynamics of an antiferromagnet in a ferromagnet/antiferromagnet heterostructure Fe/GdFeO₃ via an all-optical method. After laser irradiation, the terahertz spin precession is hard to be excited in a bare GdFeO₃ without spin reorientation phase but efficiently in Fe/GdFeO₃. Both quasi-ferromagnetic and impurity modes, as well as a phonon mode, are observed. We attribute it to the optical modification of interfacial exchange coupling between Fe and GdFeO₃. Moreover, the excitation efficiency of dynamics can be modified significantly via the pump laser influence. Our results elucidate that the interfacial exchange coupling is a feasible stimulation to efficiently excite terahertz spin dynamics in antiferromagnets. It will expand the exploration of terahertz spin dynamics for antiferromagnet-based opto-spintronic devices.     

Antiferromagnetic fluctuations in water-intercalated YBa2Cu3O6.8

Raman scattering by phononic and electronic excitations, as well as the magnetic susceptibility of water-intercalated YBa₂Cu₃O_6.8, has been studied. Direct evidence of the incorporation of OH^?-groups into the structure of the crystal has been obtained. The observed changes in the phonon spectrum and the appearance of the spectrum of antiferromagnetic fluctuations with an increased exchange coupling constant imply the localization of carriers and suppression of superconductivity. Change in the resonance behavior of the two-magnon scattering of light indicates the transformation of the electronic structure in crystallites absorbing water.     

Antiferromagnetic order and 4f-instability of CePb3

We have measured the static magnetic susceptibility of CePb₃ and LaPb₃ between 0.5 and 1,000 K and 1.5 and 900 K, respectively and the specific heat of CePb₃ between 1.5 and 40 K. The data show clearly an antiferromagnetic phase transition at 1.25 K. The order occurs in a doublet 4f groundstate whose entropy is removed only partially by long range order. There are strong indications for quadrupole-quadrupole interactions enhancing the ordering energy over that from spin spin interactions alone. The CEF splittings seem to depend on temperature. The 4f-instability in CePb₃ is quite weak.