Thermodynamics of continuous media with electromagnetic fields

The thermodynamics of an electrically charged, multicomponent continuous medium with electromagnetic fields is analysed in the non-relativistic limit. Applying locally the first and second law of thermodynamics and Maxwell's equations for a linear theory of electromagnetism, three equations characterising the continuous medium are derived: a thermostatic equilibrium equation, a reversible and an irreversible thermodynamic evolution equation. For a local thermodynamic equilibrium, explicit expressions for the temperature and the chemical potentials in terms of the electromagnetic fields are obtained. The linear phenomenological relations describe novel effects of non-uniform electromagnetic fields on the transport equations and account also for magnetoresistance and optical tweezer

The phase transition in the localized ferromagnet EuO probed by muSR

We report results of muon spin rotation measurements performed on the ferromagnetic semiconductor EuO, which is one of the best approximations to a localized ferromagnet. We argue that implanted muons are sensitive to the internal field primarily through a combination of hyperfine and Lorentz fields. The temperature dependences of the internal field and the relaxation rate have been measured and are compared with previous theoretical predictions.Comment: 4 pages, 4 figure

Ferrimagnetism of the magnetoelectric compound Cu2_2OSeO3_3 probed by 77^{77}Se NMR

We present a thorough $^{77}$Se NMR study of a single crystal of the magnetoelectric compound Cu$_2$OSeO$_3$. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phase transition from the high-T paramagnetic phase to a low-T ferrimagnetic state with 3/4 of the Cu$^{2+}$ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T. The transition to this 3up-1down magnetic state is not accompanied by any splitting of the NMR lines or any abrupt modification in their broadening, hence there is no observable reduction of the crystalline symmetry from its high-T cubic \textit{P}2$_1$3 space group. These results are in agreement with high resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos {\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic ($J_\text{afm}\simeq 68$ K) and one ferromagnetic ($J_\text{fm}\simeq -50$ K) nearest-neighbor exchange interaction

Orbital domain state and finite size scaling in ferromagnetic insulating manganites

55Mn and 139La NMR measurements on a high quality single crystal of ferromagnetic (FM) La0.80Ca20MnO3 demonstrate the formation of localized Mn(3+,4+) states below 70 K, accompanied with strong anomalous increase of certain FM neutron Bragg peaks. (55,139)(1/T1) spin-lattice relaxation rates diverge on approaching this temperature from below, signalling a genuine phase transition at T(tr) approx. 70 K. The increased local magnetic anisotropy of the low temperature phase, the cooling-rate dependence of the Bragg peaks, and the observed finite size scaling of T(tr) with Ca (hole) doping, are suggestive of freezing into an orbital domain state, precursor to a phase transition into an inhomogeneous orbitally ordered state embodying hole-rich walls.Comment: 4 pages, 4 figure

The Epistemological Foundations of Freud's Energetics Model.

This article aims to clarify the epistemological foundations of the Freudian energetics model, starting with a historical review of the 19th century scientific context in which Freud's research lay down its roots. Beyond the physiological and anatomical references of <i>Project for a Scientific Psychology</i> (Freud, 1895a), the physiology Freud makes reference to is in reality primarily anchored in an epistemological model derived from physics. Whilst across the Rhine, the autonomy of physiology in relation to physics was far from being accomplished, as a counterpoint, in France, the revolution in physiology driven by Claude Bernard established itself autonomously from physics,. In contrast, Freud's scientific landscape is entirely dominated by the physics elevated to the rank of an ideal science. The influence of Helmholtz, who is both a medical doctor and a physicist, has a determining influence on Freud's training. The discoveries in physics at that time, in particular the formulation of the principle of 'conservation of force' - first principle of thermodynamics - will constitute the points of reference upon which Freud will elaborate his energetics model, then subsequently, the idea of economy in his metapsychology. In this way we can trace both the historic and epistemological path that led Freud from a concept based on physics, and more specifically thermodynamic energy, to an idea of nervous energy that constitutes the basis of the concept of "quantity" as it is stated as 'first fundamental idea' in <i>Project for a Scientific Psychology</i> (Freud, 1895a). This notion will subsequently evolve, and lead Freud to the introduction of the concept of 'psychical energy,' this time in a purely metapsychological sense

Spin-dependent transport in cluster-assemblednanostructures: influence of cluster size and matrix material

Abstract.: Spin-dependent transport in granular metallic nanostructures has been investigated by means of a thermoelectric measurement. Cobalt clusters of well-defined size (〈n〉 = 15-600) embedded in copper and silver matrices show magnetic field responses of up to several hundred percent at low temperature. The experimental observations are attributed to spin mixing. The influence of cluster size and matrix are discusse

Effect of oxidation of cobalt-based nanowires on NMR spin-lattice relaxation

Nuclear spin-lattice relaxation measurements were performed on Co-based magnetic nanowires, in zero field and in 1 T applied field. A measurement method is developped that allows a confident interpretation of the experimental data. An enhanced relaxation due to a thermally activated phenomenon associated to oxidation is reported for the first time in the nuclear magnetic resonance of ferromagnetic systems. ©Springer-Verlag 2000

Spin-polarized oxygen hole states in cation deficient La(1-x)CaxMnO(3+delta)

When holes are doped into a Mott-Hubbard type insulator, like lightly doped manganites of the La(1-x)CaxMnO3 family, the cooperative Jahn-Teller distortions and the appearance of orbital ordering require an arrangement of Mn(3+)/Mn(4+) for the establishment of the insulating canted antiferromagnetic (for x<=0.1), or of the insulating ferromagnetic (for 0.1<x<= 0.2) ground state. In the present work we provide NMR evidence about a novel and at the same time puzzling effect in La(1-x)CaxMnO(3+delta) systems with cation deficience. We show that in the low Ca-doping regime, these systems exhibit a very strong hyperfine field at certain La nuclear sites, which is not present in the stoichiometric compounds. Comparison of our NMR results with recent x-ray absorption data at the Mn K edge, suggests the formation of a spin-polarized hole arrangement on the 2p oxygen orbitals as the origin of this effect.Comment: 10 pages, 4 Figures, submitted to PR