scholarly journals Temperature-dependent first-order reversal curve measurements on unusually hard magnetic low-temperature phase of MnBi

2017 ◽  
Vol 95 (2) ◽  
Author(s):  
Shreyas Muralidhar ◽  
Joachim Gräfe ◽  
Yu-Chun Chen ◽  
Martin Etter ◽  
Giuliano Gregori ◽  
...  
Keyword(s):  
Low Temperature ◽  
Temperature Phase ◽  
Temperature Dependent ◽  
First Order ◽  
Low Temperature Phase

scholarly journals Macroscopic degeneracy and order in the 3D plaquette Ising model

2015 ◽  
Vol 29 (20) ◽  
pp. 1550109 ◽  
Author(s):  
Desmond A. Johnston ◽  
Marco Mueller ◽  
Wolfhard Janke
Keyword(s):  
Low Temperature ◽  
Magnetic Order ◽  
Finite Size ◽  
Temperature Phase ◽  
Finite Size Scaling ◽  
First Order ◽  
Magnetic Order Parameter ◽  
First Order Transition ◽  
Definition Of ◽  
Low Temperature Phase

The purely plaquette 3D Ising Hamiltonian with the spins living at the vertices of a cubic lattice displays several interesting features. The symmetries of the model lead to a macroscopic degeneracy of the low-temperature phase and prevent the definition of a standard magnetic order parameter. Consideration of the strongly anisotropic limit of the model suggests that a layered, “fuki-nuke” order still exists and we confirm this with multi-canonical simulations. The macroscopic degeneracy of the low-temperature phase also changes the finite-size scaling corrections at the first-order transition in the model and we see this must be taken into account when analyzing our measurements.

Lattice Instabilities, Anharmonicity and Phase Transitions in PbTiO3 and PbZrO3

1995 ◽  
Vol 408 ◽  
Author(s):  
K. M. Rabe ◽  
U. V. Waghmare
Keyword(s):  
Phase Transitions ◽  
Low Temperature ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Structural Phase Transitions ◽  
Phonon Modes ◽  
First Order ◽  
Low Temperature Phase

AbstractMost perovskite structure oxides exhibit structural phase transitions from a hightemperature cubic phase to a distorted low-temperature phase which can be described by the freezing-in of one or more phonon modes of the cubic structure [1]. The first-order cubic-tetragonal ferroelectric transition in PbTiO3 at Tc = 763 K involves the freezing-in of a single F15 polar mode. In PbZrO3 , the structure of the antiferroelectric low-temperature orthorhombic phase is far more complicated, with forty atoms per unit cell and the freezing-in of R25 and Σ3 modes, perhaps accompanied by other modes as well [2][3].

Monoclinic-to-orthorhombic phase transition of the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal with temperature-dependent dynamic molecular disorder

2016 ◽  
Vol 72 (12) ◽  
pp. 971-980 ◽  
Author(s):  
Tze Shyang Chia ◽  
Ching Kheng Quah
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Structural Phase ◽  
Point Group ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Temperature Dependent ◽  
Space Group ◽  
Low Temperature Phase

As a function of temperature, the hexamethylenetetramine–2-methylbenzoic acid (1/2) cocrystal, C6H12N4·2C8H8O2, undergoes a reversible structural phase transition. The orthorhombic high-temperature phase in the space groupPccnhas been studied in the temperature range between 165 and 300 K. At 164 K, at2phase transition to the monoclinic subgroupP21/cspace group occurs; the resulting twinned low-temperature phase was investigated in the temperature range between 164 and 100 K. The domains in the pseudomerohedral twin are related by a twofold rotation corresponding to the matrix (100/0-10/00-1. Systematic absence violations represent a sensitive criterium for the decision about the correct space-group assignment at each temperature. The fractional volume contributions of the minor twin domain in the low-temperature phase increases in the order 0.259 (2) → 0.318 (2) → 0.336 (2) → 0.341 (3) as the temperature increases in the order 150 → 160 → 163 → 164 K. The transformation occurs between the nonpolar point groupmmmand the nonpolar point group 2/m, and corresponds to a ferroelastic transition or to at2structural phase transition. The asymmetric unit of the low-temperature phase consists of two hexamethylenetetramine molecules and four molecules of 2-methylbenzoic acid; it is smaller by a factor of 2 in the high-temperature phase and contains two half molecules of hexamethylenetetramine, which sit across twofold axes, and two molecules of the organic acid. In both phases, the hexamethylenetetramine residue and two benzoic acid molecules form a three-molecule aggregate; the low-temperature phase contains two of these aggregates in general positions, whereas they are situated on a crystallographic twofold axis in the high-temperature phase. In both phases, one of these three-molecule aggregates is disordered. For this disordered unit, the ratio between the major and minor conformer increases upon cooling from 0.567 (7):0.433 (7) at 170 Kvia0.674 (6):0.326 (6) and 0.808 (5):0.192 (5) at 160 K to 0.803 (6):0.197 (6) and 0.900 (4):0.100 (4) at 150 K, indicating temperature-dependent dynamic molecular disorder. Even upon further cooling to 100 K, the disorder is retained in principle, albeit with very low site occupancies for the minor conformer.

Order–disorder phenomena determined by high-resolution powder diffraction: the structures of tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 and tetrakis(trimethylsilyl)silane Si[Si(CH3)3]4

1999 ◽  
Vol 55 (6) ◽  
pp. 1014-1029 ◽  
Author(s):  
Robert E. Dinnebier ◽  
Wayne A. Dollase ◽  
Xavier Helluy ◽  
Jörg Kümmerlen ◽  
Angelika Sebald ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Intermediate Phase ◽  
Lattice Parameter ◽  
Temperature Phase ◽  
Space Group ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase ◽  
Low Temperature Phase

The compounds tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) and tetrakis(trimethylsilyl)silane Si[Si(CH3)3]4 (TSi) have crystal structures with the molecules in a cubic closed-packed (c.c.p.) stacking. At room temperature both structures have space group Fm{\bar 3}m (Z = 4) with a = 13.5218 (1) Å, V = 2472.3 (1) Å3 for TSi, and a = 12.8902 (2) Å, V = 2141.8 (1) Å3 for TC. X-ray scattering data can be described by a molecule with approximately sixfold orientational disorder, ruling out a structure with free rotating molecules. Upon cooling, TSi exhibits a first-order phase transition at T c = 225 K, as is characterized by a jump of the lattice parameter of Δa = 0.182 Å and by an exothermal maximum in differential scanning calorimetry (DSC) with ΔH = 11.7 kJ mol−1 and ΔS = 50.0 J mol−1 K−1. The structure of the low-temperature phase is refined against X-ray powder data measured at 200 K. It has space group P2 13 (Z = 4), a = 13.17158 (6) Å and V = 2285.15 (2) Å3. The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as is shown by analyzing distances between atoms and by calculations of the lattice energy in dependence on the orientations of the molecules. TC has a phase transition at T c1 = 268 K, with Δa 1 = 0.065 Å, ΔH 1 = 3.63 kJ mol−1 and ΔS 1 = 13.0 J mol−1 K−1. A second first-order phase transition occurs at T c2 = 225 K, characterized by Δa 2 = 0.073 Å, ΔH 2 = 6.9 kJ mol−1 and ΔS 2 = 30.0 J mol−1 K−1. The phase transition at higher temperature has not been reported previously. New NMR experiments show a small anomaly in the temperature dependence of the peak positions in NMR to occur at T c2. Rietveld refinements were performed for the low-temperature phase measured at T = 150 K [space group P2 13, lattice parameter a = 12.609 (3) Å], and for the intermediate phase measured at T = 260 K [space group Pa{\bar 3}, lattice parameter a = 12.7876 (1) Å]. The low-temperature phase of TC is formed isostructural to the low-temperature phase of TSi. In the intermediate phase the molecules exhibit a twofold orientational disorder.

Low‐temperature phase of yttrium iron garnet (YIG) and its first‐order magnetoelectric effect

1988 ◽  
Vol 64 (10) ◽  
pp. 5659-5661 ◽  
Author(s):  
Eiji Kita ◽  
Shunsuke Takano ◽  
Akira Tasaki ◽  
Kiiti Siratori ◽  
Kay Kohn ◽  
...  
Keyword(s):  
Low Temperature ◽  
Yttrium Iron Garnet ◽  
Magnetoelectric Effect ◽  
Temperature Phase ◽  
Yttrium Iron ◽  
First Order ◽  
Iron Garnet ◽  
Low Temperature Phase
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