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Landau theory
About: Landau theory is a research topic. Over the lifetime, 2882 publications have been published within this topic receiving 57078 citations.
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TL;DR: The zero-field susceptibility of Cu(NH4)2Br4.2H2O has been measured, using an a.c. induction method, and the transition temperature has been determined independently as Tc=1.773 ± 0.001 K, by heat-capacity measurements on the same sample.
20 citations
TL;DR: In this paper, the authors have synthesized La0.7Ca0.2Sr0.1MnO3 sample using two different methods: the solid-state reaction (S1) and the sol-gel process (S2).
Abstract: We have synthesized La0.7Ca0.2Sr0.1MnO3 sample using two different methods: the solid-state reaction (S1) and the sol–gel process (S2). Structural, morphological, infrared and magnetic properties were investigated by X-ray diffraction, scanning electron microscopy, Spectrum Two FT-IR Spectrometer and vibrating sample magnetometer. Despite the various conditions employed in the elaboration, the crystallographic study shows that our samples are single phase and crystallize in orthorhombic system with Pnma space group. A small difference appears in the microstructural and magnetic properties. The Curie temperature TC is found to be 308–256 K for S1 and S2 respectively. A large magnetocaloric effect has been observed in both samples, besides; the relative cooling power for S2 is bigger than S1. It attains exactly 250.75 J kg−1 under a magnetic applied field of 5 T. These results show that the elaboration process has an important impact on the magnetic and magnetocaloric properties. Furthermore, the importance of the magnetoelastic coupling and electron interaction in the magnetocaloric properties of manganite was confirmed by the analysis of Landau theory.
20 citations
TL;DR: In this paper, the authors analyzed experimental data within the framework of thermodynamic Landau theory for second order magnetic phase transitions to describe the relationship between the magnetization, adiabatic temperature change ΔT and magnetic field in the region of a phase transition and proved that the Landau-Ginzburg equations are applicable in the case of high magnetic fields.
20 citations
TL;DR: Supporting by Landau theory and single-crystal X-ray diffraction data, re-evaluate the space group symmetry of the intermediate-temperature phase to R3‾ reveals that the low-to-intermediate temperature transition is due to competition between two different tilt patterns of the [M(CN)6 ]3- ions.
Abstract: Materials in the family of Prussian blue analogues (C₃H₅N₂)₂K[M(CN)₆], where C₃H₅N₂ is the imidazolium ion and M = Fe, Co, undergo two phase transitions with temperature: at low temperatures the imidazolium cations have an ordered configuration (C2/c) while in the intermediate- and high- temperature phases (both previously reported as R-3m) they are dynamically disordered. We show from high-resolution powder neutron diffraction data that the high-temperature phase has zero area thermal expansion in the ab plane. Supported by Landau theory and single-crystal X-ray diffraction data, we re-evaluate the space group symmetry of the intermediate-temperature phase to R-3. This reveals that the low-to-intermediate temperature transition is due to competition between two different tilt patterns of the [M(CN)₆]³- ions. Controlling the relative stabilities of these tilt patterns offers a potential means to tune the exploitable electric behaviour that arises from motion of the imidazolium guest.
20 citations
TL;DR: In this article, a study of the dielectric constant at a constant frequency of 10 kHz as a function of temperature has been performed and the results reveal the existence of new intermediate high-order commensurate phases, in agreement with pyroelectric measurements.
Abstract: BCCD exhibits a sequence of structural phase transitions from a high-symmetry orthorhombic phase to different commensurate or incommensurate phases modulated along [001]. This work reports a study of the dielectric constant at a constant frequency of 10 kHz as a function of temperature. The results are discussed within the scope of Landau theory and reveal the existence of new intermediate high-order commensurate phases, in agreement with recent pyroelectric measurements.
20 citations