Spin reversal and magnetization jumps in ErMexMn1−xO3 perovskites (Me=Ni,Co)

The erbium-based manganite ErMnO₃ has been partially substituted at the manganese site by the transition-metal elements Ni and Co. The perovskite orthorhombic structure is found from x(Ni)=0.2–0.5 in the nickel-based solid solution ErNi_xMn_1−xO₃, while it can be extended up to x(Co)=0.7 in the case of cobalt, provided that the synthesis is performed under oxygenation conditions to favor the presence of Co³⁺. Presence of different magnetic entities (i.e., Er³⁺, Ni²⁺, Co²⁺, Co³⁺, Mn³⁺, and Mn⁴⁺) leads to quite unusual magnetic properties, characterized by the coexistence of antiferromagnetic and ferromagnetic interactions. In ErNi_xMn_1−xO₃, a critical concentration x_crit(Ni)=1/3 separates two regimes: spin-canted AF interactions predominate at x<x_crit, while the ferromagnetic behavior is enhanced for x>x_crit. Spin reversal phenomena are present both in the nickel- and cobalt-based compounds. A phenomenological model based on two interacting sublattices, coupled by an antiferromagnetic exchange interaction, explains the inversion of the overall magnetic moment at low temperatures. In this model, the ferromagnetic transition-metal lattice, which orders at T_c, creates a strong local field at the erbium site, polarizing the Er moments in a direction opposite to the applied field. At low temperatures, when the contribution of the paramagnetic erbium sublattice, which varies as T⁻¹, gets larger than the ferromagnetic contribution, the total magnetic moment changes its sign, leading to an overall ferrimagnetic state. The half-substituted compound ErCo_0.50Mn_0.50O₃ was studied in detail, since the magnetization loops present two well-identified anomalies: an intersection of the magnetization branches at low fields, and magnetization jumps at high fields. The influence of the oxidizing conditions was studied in other compositions close to the 50/50=Mn/Co substitution rate. These anomalies are clearly connected to the spin inversion phenomena and to the simultaneous presence of Co²⁺ and Co³⁺ magnetic moments. Dynamical aspects should be considered to well identify the high-field anomaly, since it depends on the magnetic field sweep rate.     

Experimental investigation of AC losses and effective time constant in the high current cable

The report is dedicated to the results of AC-loss measurements in the ITER (International Thermonuclear Experimental Reactor) Nb₃Sn strand and ITER design subsize cable samples. The test facility described below includes the set of superconducting magnet systems furnished with boil-off calorimetric inserts and calorimetric schemes including gas-flow meters. The calorimetric method and the magnetization loop recording method were used simultaneously for the AC-loss measurements. The coincidence between the results of both measuring techniques was confirmed. The original calorimetric scheme makes it possible to measure the released energy during one pulse of the magnet field. The results of AC loss measurements in ITER subsize conductor samples manufactured in Russia are given as an example.     

t夸克圈对TC理论的中性PG玻色子反常耦合的影响

推出了TC理论的中性PG玻色子与规范玻色子(Z、γ、g)的总耦合拉氏量,计算了t夸克圈对中性PG玻色子衰变宽度的影响.结果表明t夸克圈能有效地增加反常耦合强度,为在实验上寻找PG玻包子提供了理论依据.     

Investigation of dynamic equilibria using NMR-spectroscopy III. Saturation transfer experiments on the hydration of pyridine-4-carbaldehyde

Spin saturation experiments can be performed by pulse techniques. Different experiments with monoexponential as well as with biexponential decay functions are shown. Such experiments are very useful for the estimation of rate constants of chemical reactions in the time range of 0.1 to 1 seconds, where classical methods as well as relaxation kinetics are unfavourable. The application of spin saturation experiments on the hydration of pyridine-4-carbaldehyde is shown.Dedicated to Prof. Dr. Dr. h. c.K. Kratzl on the occasion of his 70th birthday.     

An anomaly formula for Ray–Singer metrics on manifolds with boundary

Using the heat kernel, we derive first a local Gauss–Bonnet–Chern theorem for manifolds with a non-product metric near the boundary. Then we establish an anomaly formula for Ray–Singer metrics defined by a Hermitian metric on a flat vector bundle over a Riemannian manifold with boundary, not assuming that the Hermitian metric on the flat vector bundle is flat nor that the Riemannian metric has product structure near the boundary. Received: January 2004; Revision: February 2005; Accepted: September 2005     

The superconformal anomaly in the 1 + 1 dimensional Wess-Zumino model

The superconformal trace anomaly is worked out to one-loop order in perturbation theory for the 1+1 dimensional Wess-Zumino model.     

Speeds of sound and isothermal compressibilities in the water-rich region of aqueous 2-butoxyethanol and 2-butanone at 25°C

Speeds of sound were measured at 25°C in the water-rich region of aqueous 2-butoxyethanol (BE) and 2-butanone (BUT). Density, heat capacity, and thermal expansivity data available in literature were used to calculate isothermal compressibilities, _T . The composition derivative, N ( _T/n_B), a third derivative of Gibbs free energy, showed a peak anomaly atx _BE=0.0175 for BE-H₂O, and a bend atx _BUT=0.033 for BUT-H₂O. n_B (n_BE or n_BUT) is the amount of the solute andx _BE andx _BUT are the respective mole fractions. The location of these anomalies were the same as those of other third derivatives found earlier for the same aqueous solutions. These anomalies were shown earlier to mark the transition point across which the mixing scheme changes in a qualitative fashion.     

PSEUDO-SOLUTION ON GEODETIC OVERDETERMINED BOUNDARY VALUE PROBLEMS

A higher step of study on the GOBVPs (geodetic overdetermined boundary value problems) is reached in this paper, which covers the proposal of new concept of pseudo-solutionon the GOBVPs, its strict definition of mathematics and solving principle. The so-called pseudosolution is a harmonical function having the property of optimum approximating the given boundary values in the sense of a relevant norm. Analytical expressions of the pseudo-solutions of two typical OBVPs for biboundary surfaces in physical geodesy, the problems S—D and S—N, are obtained, which is elegant and concise in form and convenient for practice, by using the derived formulas of norms of fractional exponential Sobolev's spaces in the case of spherical biboundary. The pseudo-solution is composed of two parts: the major is the solution of classical Stokes' problem, playing control role in field representation; the minor is correction term, serving the function of synergist and precision of the gravity field. Besides, a general case o     

Magnetic nanowires via template electrodeposition

The magnetic NiFe_x nanowires were prepared via template-guided electrodeposition. Anodized nanoporous aluminum was used as a template. The pore density and dimensions of alumina templates can be controlled by anodization conditions. Magnetic nanorods (or nanowires) with various aspect ratios were prepared by controlling the electrodeposition time. SEM and TEM micrographs revealed the wire and rod shape morphologies with 50 nm in diameter and 1.5 ~ 10 μm in length. Elemental analysis and ESCA studies suggested that NiFe₃ magnetic alloy was formed. The X-ray diffraction pattern indicates that all the nanowires are stabilized in a BCC structure with a [1 1 0] texture oriented along the long axis of the nanowires. The magnetic measurement showed no hysteresis loops for the whole aspect ratios of the nanowires. Nevertheless, the magnetization is more temperature sensitive for nanowires with lower aspect ratio. This is caused by the fact that the easy magnetization axis is always parallel to the long axis of the nanowires.