A study of crystal structure, elastic, and magnetic properties of low-doped Nd 1−x Ca x MnO 3 (x 0.15) perovskites has been carried out. The ferromagnetic component is shown to increase under hole doping and, simultaneously, the temperature of the orbital order-disorder phase transition decreases. The mechanism of the concentrational transition from a weak ferromagnetic state (x = 0) to a ferromagnetic one (x > 0.15) is discussed using a two-phase model, according to which the samples consist of weak ferromagnetic and ferromagnetic phases exchange coupled at their boundary. It is found that interaction between different magnetic phases leads to spin reorientation which takes place for 0.06 x 0.1 compounds around T eff ∼ 9 K. In the temperature range from 5 to 20 K, metamagnetic behaviour is revealed for the Nd 0.92 Ca 0.08 MnO 2.98 sample. H versus T as well as T versus x magnetic phase diagrams, which are characterized by the missing of a canted phase, are proposed. The appearance of orientational transitions is explained on the basis of a magnetic analogue of the Jahn-Teller effect taking into account that the magnetic moments of Nd ions are ordered parallel to the moments of Mn ions in the ferromagnetic phase, and opposite to the direction of the weak ferromagnetic vector at T > T eff in the weak ferromagnetic phase.
The pinning induced magnetostriction in an isotropic superconductor was calculated for different sample shapes. We analyzed some special shapes for which the solution can be found analytically. The magnetostriction of a finite slab was considered. In order to determine the influence of demagnetization effects, the pinning induced magnetostriction of an infinitely long and thin strip was calculated. A simple, approximate formula can be used in particular cases to analyze the magnetostriction induced by pinning forces. In this formula the magnetostriction of a sample is connected directly with its magnetization. We also present some experimental results on high temperature superconductors which are analyzed in frames of the developed theory.
(93)Nb NMR studies were carried out for a single crystal of NbSe(2) at 73.328 MHz in the temperature range 9-300 K to investigate the normal and charge density wave (CDW) states. Detailed analysis of the NMR line shape of the central transition using a classical incommensurate model reveals the change in the conduction electron spin dynamics from above T(CDW). An increase of the Knight shift below T(CDW) reflects modification to the uniform part of the conduction electron density of states. As suggested theoretically, the Knight shift distribution is found to be directly proportional to the square of the amplitude of the CDW. The results further indicate an incommensurate CDW state in 2H-NbSe(2). Analysis of the NMR spectra using the McMillan incommensurate model suggests a large value of the discommensuration parameter (γ) which is almost temperature independent, in contrast to the much smaller value previously reported in the case of 2H-TaSe(2).
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