Critical behavior in hexagonal Y2Fe17: magnetic interaction crossover from 3D to 2D Ising model
Ministry of Industry and Information Technology of the People's Republic of China1, Nanjing University of Aeronautics and Astronautics2, Instituto Potosino de Investigación Científica y Tecnológica3, Universidad Autónoma de Ciudad Juárez4, University of Oviedo5, Suzhou University of Science and Technology6
TL;DR: In this paper, the critical behavior of single phase Y2Fe17 melt-spun ribbons with the Th2Fe 17-type crystal structure has been studied around the transition temperature (TC), where the magnetic properties show a feature changing from three-dimensional to two-dimensional Ising model.
Abstract: The critical behavior of single phase Y2Fe17 melt-spun ribbons with the Th2Fe17-type crystal structure has been studied around the transition temperature (TC). This alloy undergoes a second-order ferromagnetic (FM)–paramagnetic (PM) phase transition at TC = 301 K. Various techniques, such as the modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis, were used to determine the critical exponents that were found to be β = 0.226(3), γ = 1.296(2), and δ = 6.804(5). The universality class of the critical phenomenon in the Y2Fe17 ribbons can be explained with the help of the renormalization group theory approach, in which the magnetic properties show a feature changing from three (3D)- to two-dimensional (2D) Ising model. The first-principles calculations based on density functional theory qualitatively explain the experimental results, confirming the strong correlation between lattice atoms and critical behavior in magnetic intermetallic Y2Fe17.
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TL;DR: In this paper , the authors reported the correlation between critical behavior and magnetocaloric effect around magnetic phase transition temperature, using magnetization isotherms of Pr2Fe16Al.
5 citations
TL;DR: In this article , a study of universality class change from Mean-Field to 3D-Heisenberg in magnetocaloric compounds SmNi3-xFex was performed.
Abstract: We report a study of universality class change from Mean-Field to 3D-Heisenberg in magnetocaloric compounds SmNi3-xFex. Three conventional techniques are used to identify the universal classes: the Modified Arrott plot, Kouvel-Fisher plot, and critical isotherm technique. The calculated critical exponents were confirmed and the isotherm M(H) curves in paramagnetic state and ferromagnetic state fall in two separated universal branches. The exponents found are similar to those determined from the renormalization group approach for a heuristic mean-field (d=3,n=3) and 3D-Heisenberg (d=3,n=3) model for SmNi3 and SmNi2.2Fe0.8, respectively.
2 citations
TL;DR: In this paper , the growth of pseudocubic SrRuO 3 single-crystal thin film on a transparent and flexible muscovite is established, and the experimental results confirm that the Curie temperature T C and the magnetic properties can be effectively tuned via the mechanical strain due to the facilitation of flexible substrate.
Abstract: In an effort to explore new electronic devices with multiple functionalities, there are numerous studies of depositing perovskite oxides on flexible substrates to replace rigid silicon‐based wafer in device applications. In this study, the growth of pseudocubic SrRuO 3 single‐crystal thin film on a transparent and flexible muscovite is established. The experimental results confirm that the Curie temperature T C and the magnetic properties can be effectively tuned via the mechanical strain due to the facilitation of flexible substrate. It is found that the tensile strain increases while the compressive strain decreases the spontaneous magnetization for the thin film suffering the same ±0.24% strain. Based on the study of critical behavior, the critical exponents β = 0.543(19) and γ = 1.262(1) with the critical temperature T C = 159.04(5) K and T C = 159.10 K, respectively, are obtained by the modified Arrott plot. The set of critical exponents matches well with Widom scaling relation and the scaling equation, indicating these critical exponents are intrinsic for SrRuO3 thin films. Moreover, it is achieved that the SrRuO3 thin films exhibit a long‐range interaction coupled with 3D‐Heisenberg type.
1 citations
TL;DR: In this article , the crystal structure, magnetic, and magnetocaloric effect properties in the intermetallic compounds SmNi3−xFex using a phenomenological model based on Landau mean-field theory and Maxwell relation were investigated.
Abstract: In this study, we investigate the crystal structure, magnetic, and magnetocaloric effect properties in the intermetallic compounds SmNi3−xFex using a phenomenological model based on Landau mean-field theory and Maxwell relation (conventional method). SmNi3−xFex compounds were prepared under high pure argon by arc melting. To minimize the amount of other possible impurity phases, the ingots were heat-treated at 1073 K for seven days. X-ray diffraction (XRD) under and without an applied magnetic field was used for the structural study. Rietveld analysis with FullProf computer code was used to analyze X-ray diffraction data. The magnetization against temperature was measured under several applied magnetic fields. After the partial substitutions of nickel atom with iron one, we notice an increase of cell parameters. In addition, Curie temperature value increases significantly with the increase of iron content. According to the Landau model, SmNi3−xFex compounds exhibit a second-order magnetic phase transition. The magnetic entropy change was determined with theoretical and experimental methods. Finally, a comparison between theoretical magnetic entropy change and the experimental show an agreement between the two methods.
01 Jan 2017
TL;DR: In this article, two methods for assembling Y2Fe17 rapidly quenched ribbons into heat exchangers of desired geometry stacked 100 mm thick plates with 100 mm gaps are discussed.
Abstract: Magnetic refrigerants are used as heat exchangers to provide rapid heat transfer between magnetocaloric materials and heat-transfer liquid. An important question is how to turn bulk magnetocaloric materials into porous structures with superior heat transfer properties and cooling performance. We discuss two methods for assembling Y2Fe17 rapidly quenched ribbons into heat exchangers of desired geometry stacked 100 mm thick plates with 100 mm gaps: the first method consists in gluing rapidly quenched ribbons using thermoconductive epoxy; the second is sintering stacked ribbons at a temperature of 30 K below the melting point of the Y2Fe17 phase. These approaches are promising with regards to making near-net shaped magnetic refrigerants. We report on adiabatic temperature change Delta T-ad, magnetic entropy change Delta S-m and thermal conductivity lambda of rapidly quenched Y2Fe17 ribbons, obtained at different quenching rates. A direct correlation between the lattice parameters of the Y2Fe17, Delta T-ad and Delta S-m in rapidly quenched samples is observed. (C) 2016 Elsevier B.V. All rights reserved.
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Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
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TL;DR: In this paper, the formal relationship between US Vanderbilt-type pseudopotentials and Blochl's projector augmented wave (PAW) method is derived and the Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional.
Abstract: The formal relationship between ultrasoft (US) Vanderbilt-type pseudopotentials and Bl\"ochl's projector augmented wave (PAW) method is derived. It is shown that the total energy functional for US pseudopotentials can be obtained by linearization of two terms in a slightly modified PAW total energy functional. The Hamilton operator, the forces, and the stress tensor are derived for this modified PAW functional. A simple way to implement the PAW method in existing plane-wave codes supporting US pseudopotentials is pointed out. In addition, critical tests are presented to compare the accuracy and efficiency of the PAW and the US pseudopotential method with relaxed core all electron methods. These tests include small molecules $({\mathrm{H}}_{2}{,\mathrm{}\mathrm{H}}_{2}{\mathrm{O},\mathrm{}\mathrm{Li}}_{2}{,\mathrm{}\mathrm{N}}_{2}{,\mathrm{}\mathrm{F}}_{2}{,\mathrm{}\mathrm{BF}}_{3}{,\mathrm{}\mathrm{SiF}}_{4})$ and several bulk systems (diamond, Si, V, Li, Ca, ${\mathrm{CaF}}_{2},$ Fe, Co, Ni). Particular attention is paid to the bulk properties and magnetic energies of Fe, Co, and Ni.
57,691 citations
TL;DR: In this article, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed and the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure is discussed.
Abstract: In spite of intrinsic limitations, neutron powder diffraction is, and will still be in the future, the primary and most straightforward technique for magnetic structure determination. In this paper some recent improvements in the analysis of magnetic neutron powder diffraction data are discussed. After an introduction to the subject, the main formulas governing the analysis of the Bragg magnetic scattering are summarized and shortly discussed. Next, we discuss the method of profile fitting without a structural model to get precise integrated intensities and refine the propagation vector(s) of the magnetic structure. The simulated annealing approach for magnetic structure determination is briefly discussed and, finally, some features of the program FullProf concerning the magnetic structure refinement are presented and discussed. The different themes are illustrated with simple examples.
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01 Jan 1971
TL;DR: In this article, the authors present a paperback edition of a distinguished book, originally published by Clarendon Press in 1971, which is at the level at which a graduate student who has studied condensed matter physics can begin to comprehend the nature of phase transitions, which involve the transformation of one state of matter into another.
Abstract: This is a paperback edition of a distinguished book, originally published by Clarendon Press in 1971. It was then the first text on critical phenomena, a field that has enjoyed great activity for the past twenty years and that still continues to attract much attention. The book is at the level at which a graduate student who has studied condensed matter physics can begin to comprehend the nature of phase transitions, which involve the transformation of one state of matter into another. (A simple example is the melting of a solid to become a liquid.) Such a transformation is termed 'critical' when, after a certain amount of the substance changes phase, the entire bulk virtually instantaneously also makes the transition. A second, updated edition is planned for future publication, but in the mean time this paperback reissue will be useful in teaching the fundamental principles of this extremely interesting subject.
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