Magnetic susceptibility and heat capacity measurements are used to infer information about the short-range magnetic order above the Néel temperature T N and the antiferromagnetically ordered states below T N of quasione-dimensional (quasi-1D) CuSb 2 O 6 , NiTa 2 O 6 , and CoSb 2 O 6 . It is shown that two antiferromagnetic sublattices, oriented at 90 • to one another, are likely present in NiTa 2 O 6 and CoSb 2 O 6 . Application of magnet field parallel to the quasi-1D chains of one sublattice is perpendicular to the chains of the other sublattice. This results in two antiferromagnetic transitions when the magnetic field H 2 T (∼0.2 meV). The anisotropic influence of magnetic field on the antiferromagnetic state leads to a magnetocaloric effect that is fully investigated in this work. The effect is associated with competition among Néel, dimer, and spin-liquid states that are all present at T N .
The magnetic, thermal, and optical properties of single-crystalline CoTaO and FeTaO are reported. Optical dichroism was observed in CoTaO. Magnetic susceptibility χ(T) measurements reveal long-range antiferromagnetic order with Néel temperatures [Formula: see text] K and 8.11(5) K, respectively, and anisotropy in χ. The thermal expansion coefficients exhibit significant anisotropy and the influence of the magnetic ions and long-range order. A structural phase transition to orthorhombic occurs below T for FeTaO. Magnetic field H lowers T with its affect largest when H is directed along either [1 1 0] or [1 [Formula: see text] 0], and smallest when directed along [0 0 1]. This leads to an anisotropic magnetocaloric effect that is investigated through measurements of the specific heat and magnetization in applied magnetic field.
Sleep Slow Oscillations (SSOs), paradigmatic EEG markers of cortical bistability (alternation between cellular downstates and upstates), and sleep spindles, paradigmatic EEG markers of thalamic rhythm, are two hallmarks of sleeping brain. Selective thalamic lesions are reportedly associated to reductions of spindle activity and its spectrum~14 Hz (sigma), and to alterations of SSO features. This apparent, parallel behavior suggests that thalamo-cortical entrainment favors cortical bistability. Here we investigate temporally-causal associations between thalamic sigma activity and shape, topology, and dynamics of SSOs. We recorded sleep EEG and studied whether spatio-temporal variability of SSO amplitude, negative slope (synchronization in downstate falling) and detection rate are driven by cortical-sigma-activity expression (12-18 Hz), in 3 consecutive 1 s-EEG-epochs preceding each SSO event (Baselines). We analyzed: (i) spatial variability, comparing maps of baseline sigma power and of SSO features, averaged over the first sleep cycle; (ii) event-by-event shape variability, computing for each electrode correlations between baseline sigma power and amplitude/slope of related SSOs; (iii) eventby-event spreading variability, comparing baseline sigma power in electrodes showing an SSO event with the homologous ones, spared by the event. The scalp distribution of baseline sigma power mirrored those of SSO amplitude and slope; event-by-event variability in baseline sigma power was associated with that in SSO amplitude in fronto-central areas; within each SSO event, electrodes involved in cortical bistability presented higher baseline sigma activity than those free of SSO. In conclusion, spatio-temporal variability of thalamocortical entrainment, measured by background sigma activity, is a reliable estimate of the cortical proneness to bistability.
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