Search results for "HYSTERESIS"

Electromagnetic response of LaO_0.94F_0.06FeAs: AC susceptibility and microwave surface resistance

2009

We discuss on the electromagnetic response of a polycrystalline sample of LaO_0.94F_0.06FeAs exposed to DC magnetic fields up to 10 kOe. The low- and high-frequency responses have been investigated by measuring the AC susceptibility at 100 kHz and the microwave surface resistance at 9.6 GHz. At low as well as high DC magnetic fields, the susceptibility strongly depends on the amplitude of the AC driving field, highlighting enhanced nonlinear effects. The field dependence of the AC susceptibility exhibits a magnetic hysteresis that can be justified considering the intragrain-field-penetration effects on the intergrain critical current density. The microwave surface resistance exhibits a cloc…

Zeolite-gas systems and solar refrigeration : a study of the adsorptive properties at high pressures in the R22 freon-13X zeolite and ammonia-13X zeo…

1990

The adsorption of ammonia and R22 freon on 13X zeolite was studied in the conditions of possible use of these fluids in heat machines for solar refrigeration. The ranges of temperature and pressure, investigated in this study, extended from 0 to 80 °C and from 10-1 to 6 105 Pa respectively. The adsorption isotherms were collected by microgravimetry using a thermobalance specially built to be used in aggressive gases at pressures up to 106 Pa. Weak hysteresis was detected when ammonia was desorbed below 80 °C. A critical study concerning both applicability of classical adsorption equations (Dubinin-Radushkevitch and Langmuir) and comparison with other zeolite-gas systems is presented. Compar…

Exploring the High-Temperature Frontier in Molecular Nanomagnets: From Lanthanides to Actinides.

2019

Molecular nanomagnets based on mononuclear metal complexes, also known as single-ion magnets (SIMs), are crossing challenging boundaries in molecular magnetism. From an experimental point of view, this class of magnetic molecules has expanded from lanthanoid complexes to both d-transition metal and actinoid complexes. From a theoretical point of view, more and more improved models have been developed, and we are now able not only to calculate the electronic structure of these systems on the basis of their molecular structures but also to unveil the role of vibrations in the magnetic relaxation processes, at least for lanthanoid and d-transition metal SIMs. This knowledge has allowed us to o…

A Dysprosium Metallocene Single-Molecule Magnet Functioning at the Axial Limit

2017

Abstraction of a chloride ligand from the dysprosium metallocene [(Cpttt)2DyCl] (1Dy Cpttt=1,2,4‐tri(tert‐butyl)cyclopentadienide) by the triethylsilylium cation produces the first base‐free rare‐earth metallocenium cation [(Cpttt)2Dy]+ (2Dy) as a salt of the non‐coordinating [B(C6F5)4]− anion. Magnetic measurements reveal that [2Dy][B(C6F5)4] is an SMM with a record anisotropy barrier up to 1277 cm−1 (1837 K) in zero field and a record magnetic blocking temperature of 60 K, including hysteresis with coercivity. The exceptional magnetic axiality of 2Dy is further highlighted by computational studies, which reveal this system to be the first lanthanide SMM in which all low‐lying Kramers doub…

Unemployment dynamics and NAIRU estimates for accession countries: A univariate approach

2005

Abstract In this paper we test for hysteresis effects versus the natural rate hypothesis on unemployment rates of new members in the European Union (EU) using unit root tests that account for the presence of level shifts. In addition, we estimate the non-accelerating inflation rate of unemployment (NAIRU) from a univariate perspective. The precision of these NAIRU are investigated by studying two sources of inaccuracy that derive from the estimation of the break points, and the estimation of the autoregressive parameters. The results indicate up to four structural breaks in the NAIRU of transition countries that can be associated with institutional changes from implementing market-oriented …

Magnetic characteristics of industrial dust from different sources of emission: A case study of Poland

2015

Abstract Dust emission and deposition in topsoil have negative effect on individual components of the ecosystem. In addition to routine geochemical analyses, magnetic measurements may provide useful complementary information related to the type, concentration and grain-size distribution of the technogenic magnetic particles (TMPs) and thus the degree of contamination of the environment. The aim of this contribution is to use magnetic parameters in distinguishing dust from a wide range of sources of air pollution (power industry, cement, coke, ceramic industries and biomass combustion). We measured magnetic susceptibility, hysteresis parameters and thermomagnetic curves. Our results suggest …

Dynamic Preisach Hysteresis Model for Magnetostrictive Materials for Energy Application

2013

Pressure and Thermally Induced Spin Crossover in a 2D Iron(II) Coordination Polymer {Fe[bipy(ttr)2]}n

2021

Using magnetic measurements and UV -visible spectroscopy we have studied the pressure influence on the spin crossover (SCO) properties of the 2D Fe (II) coordination polymer formulated {Fe[bipy(ttr) 2 ]} n . At variable temperature and fixed pressure, we have measured the magnetic property of this compound. Under different pressures and at room temperature, the visible spectroscopy has been observed. The magnetic experiment displays a two-step spin crossover behavior under pressure. The visible spectroscopic measurements at room temperature show a spin crossover with an asymmetric hysteresis at 0.4GPa.

Essential Measurements for Finite Element Simulations of Magnetostrictive Materials

2018

We discuss which magnetoelastic material properties are essential to measure in order to model magnetostrictive materials in finite element simulations. We show knowing the magnetic constitutive relation is sufficient, if the elastic behavior without magnetic field is known a priori. We neglect hysteresis, and our starting point is to express the effect of mechanical deformation on the magnetic constitutive relation with a small strain tensor and magnetic flux density. It follows that the (energetic) state of a magnetostrictive material is independent of its history. Then, a certain choice of history allows us to keep magnetism and elasticity distinct. We demonstrate with open source softwa…

Quantum Tunneling of Magnetization under Pressure in the High-Spin Mn12 Molecular System

2004

Experimental and theoretical investigations of quantum tunneling magnetization in the high-spin cluster [Mn 1 2 O 1 2 (CH 3 COO) 1 6 (H 2 O) 4 ].2CH 3 COOH.4H 2 O under pressure have been performed. The main observation is that the blocking temperature and hysteresis width decrease under the effect of pressure. However, the position of the steps in the magnetization versus field curve does not change noticeably as pressure increases. A theoretical examination of the pressure influence on the relaxation rate and magnetization has been carried out taking into consideration the quantum tunneling effects. The qualitative agreement between theory and experiment has been achieved both at atmosphe…