Ferrimagnetism of the magnetoelectric compound Cu2OSeO3 probed by 77Se NMR

We present a thorough 77Se nuclear-magnetic-resonance (NMR) study of a single crystal of the magnetoelectric compound Cu 2OSeO3. 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 Cu2+ 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 in the crystal symmetry from its high- T cubic P 213 space group. These results are in agreement with high-resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos [Phys. Rev. B 78, 094416 (2008)]10.1103/PhysRevB.78.094416. We also develop a mean-field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic (Jafm ≃68 K) and one ferromagnetic (J fm ≃-50 K) nearest-neighbor exchange interaction. © 2010 The American Physical Society

Magnetic properties of the magnetoelectric compound Cu2OSeO3: Magnetization and 77Se NMR study

We present magnetization and77Se Nuclear Magnetic Resonance (NMR) measurements in single crystals of the magneteoelectric compound Cu2OSeO3. The temperature and field dependence of the magnetization suggest a ferrimagnetic ordering at Tc≃ 60 K in a 3up-1down configuration. The easy axis of the magnetization is along the [100] crystallographic direction. The77Se NMR line shape data collected at 14.09 T are consistent with the symmetries imposed by the cubic P213 space group in the temperature range 20-290 K and confirm that the magnetic transition is not accompanied by any lowering of the crystal symmetry as has recently been proposed by Bos et al. [Phys. Rev. B 78 094416 (2008)]

From the Principle of Inertia to the Death Drive: The Influence of the Second Law of Thermodynamics on the Freudian Theory of the Psychical Apparatus.

In the Freudian theory of the psychical apparatus, the introduction from the 1920s onward of the second drive dualism appears as a major turning point. The idea of a "death drive," first expressed in Beyond the Pleasure Principle (Freud, 1920), is generally considered to be a new concept, one that represents a break with Freud's previous thinking. It has often surprised the scholars because it seemed, at first sight, difficult to reconcile with the idea of the singularity of living organisms within which the psychical functions form an integral part. Our research aims to demonstrate that the theory of the death drive does not represent a complete change in direction for Freud. It is present, in essence, in his earliest work, to the extent that the "principle of inertia" described in 1895 in A Project for a Scientific Psychology (Freud, 1895) can be seen as a precursor to the death drive. Based on a reading of Freud's early formulations of his ideas, we aim to bring to light how certain aporias that seem inherent to the concept of the death drive can be overcome if we consider them in the context of an epistemological model that draws on the paradigms of physics which were conveyed by the Helmholtz School. Namely, we can consider the idea of death drive in reference to the principle of entropy and the laws of thermodynamics

Hyperpolarizing gases via dynamic nuclear polarization and sublimation.

A high throughput method was designed to produce hyperpolarized gases by combining low-temperature dynamic nuclear polarization with a sublimation procedure. It is illustrated by applications to 129Xe nuclear magnetic resonance in xenon gas, leading to a signal enhancement of 3 to 4 orders of magnitude compared to the room-temperature thermal equilibrium signal at 7.05 T