skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Structural phase transitions in isotropic magnetic elastomers

Abstract

Magnetic elastomers represent a new type of materials that are “soft” matrices with “hard” magnetic granules embedded in them. The elastic forces of the matrix and the magnetic forces acting between granules are comparable in magnitude even under small deformations. As a result, these materials acquire a number of new properties; in particular, their mechanical and/or magnetic characteristics can depend strongly on the polymer matrix filling with magnetic particles and can change under the action of an external magnetic field, pressure, and temperature. To describe the properties of elastomers, we use a model in which the interaction of magnetic granules randomly arranged in space with one another is described in the dipole approximation by the distribution function of dipole fields, while their interaction with the matrix is described phenomenologically. A multitude of deformation, magnetic-field, and temperature effects that are described in this paper and are quite accessible to experimental observation arise within this model.

Authors:
;  [1]
  1. National Research Center “Kurchatov Institute” (Russian Federation)
Publication Date:
OSTI Identifier:
22617246
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 122; Journal Issue: 6; Other Information: Copyright (c) 2016 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; APPROXIMATIONS; COMPARATIVE EVALUATIONS; DEFORMATION; DIPOLES; DISTRIBUTION; DISTRIBUTION FUNCTIONS; ELASTOMERS; INTERACTIONS; MAGNETIC FIELDS; PHASE TRANSFORMATIONS; RANDOMNESS; TEMPERATURE DEPENDENCE

Citation Formats

Meilikhov, E. Z., E-mail: meilikhov@yandex.ru, and Farzetdinova, R. M. Structural phase transitions in isotropic magnetic elastomers. United States: N. p., 2016. Web. doi:10.1134/S1063776116060170.
Meilikhov, E. Z., E-mail: meilikhov@yandex.ru, & Farzetdinova, R. M. Structural phase transitions in isotropic magnetic elastomers. United States. doi:10.1134/S1063776116060170.
Meilikhov, E. Z., E-mail: meilikhov@yandex.ru, and Farzetdinova, R. M. 2016. "Structural phase transitions in isotropic magnetic elastomers". United States. doi:10.1134/S1063776116060170.
@article{osti_22617246,
title = {Structural phase transitions in isotropic magnetic elastomers},
author = {Meilikhov, E. Z., E-mail: meilikhov@yandex.ru and Farzetdinova, R. M.},
abstractNote = {Magnetic elastomers represent a new type of materials that are “soft” matrices with “hard” magnetic granules embedded in them. The elastic forces of the matrix and the magnetic forces acting between granules are comparable in magnitude even under small deformations. As a result, these materials acquire a number of new properties; in particular, their mechanical and/or magnetic characteristics can depend strongly on the polymer matrix filling with magnetic particles and can change under the action of an external magnetic field, pressure, and temperature. To describe the properties of elastomers, we use a model in which the interaction of magnetic granules randomly arranged in space with one another is described in the dipole approximation by the distribution function of dipole fields, while their interaction with the matrix is described phenomenologically. A multitude of deformation, magnetic-field, and temperature effects that are described in this paper and are quite accessible to experimental observation arise within this model.},
doi = {10.1134/S1063776116060170},
journal = {Journal of Experimental and Theoretical Physics},
number = 6,
volume = 122,
place = {United States},
year = 2016,
month = 6
}
  • With decreasing temperature, the magnetic metal NaV{sub 6}O{sub 11} undergoes two structural phase transitions (at 245 and 40 K) and exhibits anomalous electrical and magnetic properties. To probe the origin of these structural, electrical and magnetic properties, the electronic structures of NaV{sub 6}O{sub 11} were calculated for its crystal structures at room temperature, 200 K, and 30 K using the extended Hueckel tight-binding band method. The 245 and 40 K structural phase transitions are not caused by a charge density wave instability, but by the lowering of the energy levels lying well below the Fermi level. In the magnetic metallicmore » state of NaV{sub 6}O{sub 11}, obtained by the spin-polarization of the partially filled d-block bands, the electrical conductivity of NaV{sub 6}O{sub 11} is predicted to be greater along the c-direction than in the ab plane, in agreement with experiment. Our study indicates that the unpaired electrons of NaV{sub 6}O{sub 11} reside mainly in the V{sub 3}O{sub 11} rather than in the V{sub 3}O{sub 8} layers. The anomalies of the {rho}-vs-T plot is explained by considering the effect of disordered magnetic moments on electrical conductivity. 27 refs., 15 figs., 3 tabs.« less
  • The coefficients of the thermal expansion and the specific heat of Pr{sub 2}NiO{sub 4} single crystals have been measured in order to study the thermodynamic and structural properties of the low-temperature structural and magnetic phase transitions. We find large, strongly anisotropic length changes and first-order specific heat anomalies at the low-temperature tetragonal (LTT) to low-temperature orthorhombic (LTO) transition at {ital T}{sub LT}. These anomalies imply huge anisotropic uniaxial pressure dependences of {ital T}{sub LT}. The anisotropy and size of the length changes indicate that the LTT phase occurs in order to minimize the effects of the ionic size mismatch. Themore » discontinuities in both properties at {ital T}{sub LT} in Pr{sub 2}NiO{sub 4} are orders of magnitude larger than those in the high-{ital T}{sub c} superconducting cuprates and the pressure dependences differ even qualitatively. Besides the anomalies at {ital T}{sub LT} we find two first-order phase transitions in the thermal expansion of Pr{sub 2}NiO{sub 4} at {ital T}{approx_equal}90K due to the reorientation of the Ni spins in the quasi-two-dimensional antiferromagnet. No corresponding anomalies could be resolved in the specific heat, which implies a very large and anisotropic pressure dependence of these magnetic transitions and thus shows an intimate coupling between structural and magnetic degrees of freedom in Pr{sub 2}NiO{sub 4}. {copyright} {ital 1996 The American Physical Society.}« less
  • Measurements of the thermal expansion of a single crystal of La{sub 0.835}Sr{sub 0.165}MnO{sub 3} were performed under hydrostatic pressure of up to 9 kbar. The P-T phase diagram is established for the structural and magnetic phase transitions. Pressure is found to enhance the ferromagnetic coupling and to weaken the stability of the low-temperature orthorhombic phase by reducing the bending of the Mn-O-Mn bond. The decrease in the temperature T{sub S} of the structural phase transition and the increase in the Curie temperature with increasing pressure leads to the two phase boundaries crossing at a pressure of about 3 kbar. Themore » peculiar behavior of the T{sub S} and T{sub C} in the vicinity of the crossing point demonstrates a strong coupling between structural distortion and magnetic ordering in the La{sub 0.835}Sr{sub 0.165}MnO{sub 3} compound. {copyright} {ital 1997} {ital The American Physical Society}« less
  • We present results from a detailed experimental investigation of LaFeAsO, the parent material in the series of ``FeAs'' based oxypnictide superconductors. Upon cooling this material undergoes a tetragonal-orthorhombic crystallographic phase transition at ~160 K followed closely by an antiferromagnetic ordering near 145 K. Analysis of these phase transitions using temperature dependent powder X-ray and neutron diffraction measurements is presented. A magnetic moment of ~0.35 Bohr magneton per iron is derived from Mossbauer spectra in the low temperature phase. Evidence of the structural transition is observed at temperatures well above the structural transition (up to near 200 K) in the diffractionmore » data as well as the polycrystalline elastic moduli probed by resonant ultrasound spectroscopy measurements. The effects of the two phase transitions on the transport properties (resistivity, thermal conductivity, Seebeck coefficient, Hall coefficient), heat capacity, and magnetization of LaFeAsO are also reported, including an order of magnitude drop in the inferred carrier concentration below 160 K. The results suggest that the structural distortion leads to a localization of carriers on Fe, producing small local magnetic moments which subsequently order antiferromagnetically upon further cooling. Evidence of strong electron-phonon interactions in the high-temperature tetragonal phase is also observed.« less
  • We present results of transport and magnetic properties and heat capacity measurements on polycrystalline CeFeAsO, PrFeAsO and NdFeAsO. These materials undergo structural phase transitions, spin density wave-like magnetic ordering of small moments on iron and antiferromagnetic ordering of rare-earth moments. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, Hall coefficient and magnetoresistance are reported. The magnetic behavior of the materials have been investigated using Moessbauer spectroscopy and magnetization measurements. Transport and magnetic properties are affected strongly by the structural and magnetic transitions, suggesting significant changes in the band structure and/or carrier mobilities occur, and phonon-phonon scattering ismore » reduced upon transformation to the low-temperature structure. Results are compared with recent reports for LaFeAsO, and systematic variations in properties as the identity of Ln is changed are observed and discussed. As Ln progresses across the rare-earth series from La to Nd, an increase in the hole contributions to the Seebeck coefficient and increases in magnetoresistance and the Hall coefficient are observed in the low-temperature phase. Analysis of hyperfine fields at the iron nuclei determined from Moessbauer spectra indicates that the moment on Fe in the orthorhombic phase is nearly independent of the identity of Ln, in apparent contrast to reports of powder neutron diffraction refinements.« less