Magnetic Anisotropy Constants of Epitaxial (110) Fe/GaAs Films from 77k To 293k Studied by Magneto-Resistance

1989 ◽  
Vol 151 ◽  
Author(s):  
Daniel K. Lottis ◽  
G. A. Prinz ◽  
E. Dan Dahlberg
Keyword(s):  
Phase Transition ◽  
Uniaxial Anisotropy ◽  
Epitaxial Films ◽  
Effective Anisotropy ◽  
First Order ◽  
First Order Phase Transition ◽  
Gaas Films ◽  
First Order Phase ◽  
Magneto Resistance

ABSTRACTA first-order phase transition in the magnetization of Fe films, driven by an applied magnetic field, was first reported by Hathaway and Prinz [1]. Further studies were performed on this phase transition using anisotropic magnetoresistance measurements by Riggs and Dahlberg [2]. Here we report the extension of these studies to include temperatures between 77K and 293K. Emphasis is on a determination of the fourth-order and uniaxial anisotropy constants (K1 and Ku). It is shown that the temperature dependence of the anisotropy energies in these films varies with thickness, which may be useful in sorting out the origin and magnitude of different contributions to the total effective anisotropy. The present study suggests that similar studies of (110) iron on other substrates might contribute to achieving a better understanding of in-plane anisotropies in epitaxial films.

Effect of Strain on Barium Titanate Epitaxial Films

2013 ◽  
Vol 547 ◽  
pp. 139-144
Author(s):  
Lye Hock Ong ◽  
A.M. Alrub ◽  
Khian Hooi Chew
Keyword(s):  
Thin Films ◽  
Phase Transition ◽  
Free Energy ◽  
Epitaxial Films ◽  
Ferroelectric Films ◽  
Eighth Order ◽  
First Order ◽  
First Order Phase Transition ◽  
Highly Strained ◽  
First Order Phase

Landau-Ginzburg free energy expression with the normalized coefficients is used to elucidate the phase transition properties of strained ferroelectric films. In particular, we investigate the need to include higher order free energy terms for epitaxial strained BaTiO3 thin films. Our study reveals that the inclusion of eighth-order expression into the free energy is crucial in determining the phase transition of highly-strained BaTiO3 epitaxial films normally grown on thick cubic substrates. The phase transition is found to be second order but the unstrained film undergoes the first order phase transition. On the order hand, the calculation based on the usual sixth-order Landau-Ginzburg expression show that the films have no phase transition, which is contrary to the experimental observations.

WEIGHT RATIO FIXING AT FIRST ORDER PHASE TRANSITIONS

1992 ◽  
Vol 03 (05) ◽  
pp. 1109-1117
Author(s):  
THOMAS LIPPERT ◽  
KLAUS SCHILLING ◽  
PEER UEBERHOLZ ◽  
GYAN BHANOT
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Weight Ratio ◽  
Phenomenological Method ◽  
Reliable Determination ◽  
First Order ◽  
First Order Phase Transition ◽  
Two Phases ◽  
First Order Phase

The presence of strong metastabilities in computer simulations of models showing a first order phase transition hinders a reliable determination of the weight ratio between the two phases. We discuss a new phenomenological method which allows an accurate fixing of the weight ratio using the standard multihistogram procedure.

Fluxional seven-coordinated fluorido- and oxofluoridotantalates

2019 ◽  
Vol 75 (6) ◽  
pp. 1115-1125
Author(s):  
Anatoly A. Udovenko ◽  
Arseny B. Slobodyuk ◽  
Tatiana B. Emelina ◽  
Natalia M. Laptash
Keyword(s):  
Phase Transition ◽  
Central Atom ◽  
Crystal Form ◽  
Pentagonal Bipyramid ◽  
Infrared Band ◽  
First Order ◽  
First Order Phase Transition ◽  
Stretching Vibrations ◽  
First Order Phase

Seven-coordinated (NH4)2TaF7, Rb2TaF7 and Rb3TaOF6 were synthesized in single-crystal form and their structures were determined. A monocapped trigonal prism (CTP) or a pentagonal bipyramid (PB) of the TaF7 2− anion are stereochemically nonrigid and coexist in the first two compounds as a result of strong intraspheric dynamics. Upon cooling, tetragonal Rb2TaF7 undergoes a first-order phase transition at 145 K and the seven-coordinated polyhedron transforms into a regular CTP. The seven-coordinated polyhedron in (NH4)2TaF7 approaches the PB configuration as the temperature decreases. Cubic elpasolite-like Rb3TaOF6 is characterized by the simultaneous two-state coexistence of TaOF6 3− of the PB shape as rigidly reoriented and as fluxional. In the former case, the central atom is disordered over the octahedron in the unit cell, allowing the determination of the short Ta—O distance, whereas in the latter case, tantalum remains in the polyhedron center, resulting in synchronous Ta—O and Ta—F stretching vibrations appearing as the infrared band at 723 cm−1.

scholarly journals Gravitational wave signals of dark matter freeze-out

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Danny Marfatia ◽  
Po-Yan Tseng
Keyword(s):  
Phase Transition ◽  
Dark Matter ◽  
Gravitational Waves ◽  
Order Phase Transition ◽  
First Order ◽  
Stochastic Background ◽  
First Order Phase Transition ◽  
Relic Abundance ◽  
First Order Phase ◽  
Freeze Out

Abstract We study the stochastic background of gravitational waves which accompany the sudden freeze-out of dark matter triggered by a cosmological first order phase transition that endows dark matter with mass. We consider models that produce the measured dark matter relic abundance via (1) bubble filtering, and (2) inflation and reheating, and show that gravitational waves from these mechanisms are detectable at future interferometers.

scholarly journals Dark Matter production from relativistic bubble walls

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Aleksandr Azatov ◽  
Miguel Vanvlasselaer ◽  
Wen Yin
Keyword(s):  
Phase Transition ◽  
Dark Matter ◽  
Electroweak Phase Transition ◽  
First Order ◽  
Matter Production ◽  
First Order Phase Transition ◽  
Relic Abundance ◽  
Higgs Portal ◽  
First Order Phase ◽  
Gravitational Background

Abstract In this paper we present a novel mechanism for producing the observed Dark Matter (DM) relic abundance during the First Order Phase Transition (FOPT) in the early universe. We show that the bubble expansion with ultra-relativistic velocities can lead to the abundance of DM particles with masses much larger than the scale of the transition. We study this non-thermal production mechanism in the context of a generic phase transition and the electroweak phase transition. The application of the mechanism to the Higgs portal DM as well as the signal in the Stochastic Gravitational Background are discussed.

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