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search.filters.applied.f.access: openAccess × End date: 2019 × Start date: 2016 × End date: 2009 × Start date: 2000 × Has files: Yes × Type: article × Subject: Antiferromagnetic materials ×

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Now showing 1 - 3 of 3
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    High-field ESR studies of the quantum spin magnet CaCu2O 3
    (Milton Park : Taylor & Francis, 2006) Goiran, M.; Costes, M.; Broto, J.M.; Chou, F.C.; Klingeler, R.; Arushanov, E.; Drechsler, S.-L.; Büchner, B.; Kataev, V.
    We report an electron spin resonance (ESR) study of the s = 1/2 Heisenberg pseudo-ladder magnet CaCu2O3 in pulsed magnetic fields up to 40 T. At sub-terahertz frequencies we observe an ESR signal originating from a small amount of uncompensated spins residing presumably at the imperfections of the strongly antiferromagnetically correlated host spin lattice. The data give evidence that these few per cent of 'extra' spin states are coupled strongly to the bulk spins and are involved in the antiferromagnetic (AF) ordering at TN = 25 K. By mapping the frequency/resonance field diagram we have determined a small gap for magnetic excitations below TN of the order of ~0.3–0.8 meV. Such a small value of the gap explains the occurrence of the spin-flop transition in CaCu2O3 at weak magnetic fields μ0Hsf ~ 3 T. Qualitative changes of the ESR response with the increasing field strength give indications that strong magnetic fields reduce the AF correlations and may even suppress the long-range magnetic order in CaCu2O3. ESR data support scenarios with a significant role of the 'extra' spin states for the properties of low-dimensional quantum magnets.
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    Pressure-driven magnetic moment collapse in the ground state of MnO
    (Milton Park : Taylor & Francis, 2007) Kasinathan, Deepa; Koepernik, K.; Pickett, W.E.
    The zero temperature Mott transition region in antiferromagnetic, spin S = 5/2 MnO is probed using the correlated band theory LSDA + U method. The first transition encountered is an insulator-insulator volume collapse within the rocksalt structure that is characterized by an unexpected Hund's rule violating 'spin-flip' moment collapse. This spin-flip to S = 1/2 takes fullest advantage of the anisotropy of the Coulomb repulsion, allowing gain in the kinetic energy (which increases with decreasing volume) while retaining a sizable amount of the magnetic exchange energy. While transition pressures vary with the interaction strength, the spin-flip state is robust over a range of interaction strengths and for both B1 and B8 structures.
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    Magnetic-field- and temperature-dependent fermi surface of CeBiPt
    (Milton Park : Taylor & Francis, 2006) Wosnitza, J.; Goll, G.; Bianchi, A.D.; Bergk, B.; Kozlova, N.; Opahle, I.; Elgazzar, S.; Richter, Manuel; Stockert, O.; Löhneysen, H.V.; Yoshino, T.; Takabatake, T.
    The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikov–de Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15 K. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B>25 T), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification.