scholarly journals To a Question about First-Order Phase Transitions in Orthoferrites

2016 ◽  
Vol 17 (2) ◽  
pp. 193-197
Author(s):  
O.G. Medvedovs’ka ◽  
G.K. Chepurnykh ◽  
T.O. Fedorenko ◽  
S.V. Sokolov
Keyword(s):  
Magnetic Field ◽  
Phase Transitions ◽  
External Magnetic Field ◽  
Landau Theory ◽  
Second Order ◽  
First Order ◽  
First Order Phase

On the example of first-order phase transitions in orthoferrites under the influence of an external magnetic field is shown the effectiveness of the application of the Landau theory of phase transitions, commonly used in second-order phase transitions. This is especially important when used Hamiltonian is a function of many variables.

SUSCEPTIBILITY SINGULARITIES AT FIRST-ORDER PHASE TRANSITIONS

1992 ◽  
Vol 03 (05) ◽  
pp. 1071-1082 ◽  
Author(s):  
D.B. ABRAHAM ◽  
P.J. UPTON
Keyword(s):  
Magnetic Field ◽  
Correlation Function ◽  
Phase Transitions ◽  
Thermodynamic Functions ◽  
Infinite Number ◽  
Limit Point ◽  
Correlation Functions ◽  
Negative Real Axis ◽  
First Order ◽  
First Order Phase

Problems associated with analyticity of thermodynamic functions close to first-order phase transitions are briefly reviewed. The bubble model for correlation functions is then applied to planar Ising-like models at subcritical temperatures (T<Tc) with a bulk magnetic field h. The fluctuation sum is used to calculate the susceptibility χ(h) from the bubble correlation function. We show that χ(h), calculated this way, must contain an essential singularity at h=0 i.e. at the first-order phase boundary. This has important implications to metastability, where we demonstrate that if the ensemble is restricted such that the magnetization stays positive when h goes negative, χ(h) has an infinite number of poles along the negative real axis with a limit-point at h=0. For an unrestricted ensemble, a Yang-Lee circle theorem is derived.

scholarly journals Скачкообразные процессы магнитного разупорядочения, стимулированные магнитным полем в системах со структурной неустойчивостью

2020 ◽  
Vol 62 (5) ◽  
pp. 710
Author(s):  
В.И. Вальков ◽  
А.В. Головчан ◽  
В.В. Коледов ◽  
Б.М. Тодрис ◽  
В.И. Митюк
Keyword(s):  
Magnetic Field ◽  
Phase Transitions ◽  
Static Magnetic Fields ◽  
First Order ◽  
Temperature Dependences ◽  
Second Order Transition ◽  
First Order Phase ◽  
Experimental Pressure ◽  
The Magnetic Field ◽  
Theoretical Results

A theoretical analysis of the features of structural and magnetostructural first-order phase transitions in magnetocaloric helimagnetic alloys of the Mn_{1-x}Cr_{x}NiGe system has been carried out. To describe the observed displacive structural transitions hex(P6_{3}/mmc)<->orth(P_{nma}), we used the local soft mode model in the approximation of a biased harmonic oscillator. In the absence of a magnetic field, the emergence of a helimagnetic order as a structurally induced second-order transition was described in the framework of the Heisenberg model, taking into account the dependence of the exchange integrals on the structural order parameters and elastic strains. In the presence of a magnetic field, it was found that the approximation of the characteristic temperatures for the helimagnetic HM(P_{nma}) and lability temperatures of the hexagonal paramagnetic PM(P6_{3}/mmc) states, due to the influence of the magnetic field, leads to the appearance of previously unexplored peripheral magnetostructural first-order phase transitions with insignificant magnetization jumps that increase with increasing magnetic induction.In this case, as the pressure increases to 4 kbar with constant induction of the magnetic field, the peripheral transitions transform into reversible first-order magnetostructural transitions, and at even higher pressures (10-14 kbar) into full-fledged first-order magnetostructural transitions with magnetization jumps comparable with maximum value of magnetization. Experimental pressure studies of the temperature dependences of magnetization in static magnetic fields with an induction of up to 1 T and a pressure of up to 14 kbar confirm the theoretical results.

scholarly journals Black hole singularities across phase transitions

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Yan Liu ◽  
Hong-Da Lyu ◽  
Avinash Raju
Keyword(s):  
Field Theory ◽  
Black Hole ◽  
Phase Transitions ◽  
Second Order ◽  
Scalar Theory ◽  
First Order ◽  
First Order Phase

Abstract We study the behavior of black hole singularities across the Hawking-Page phase transitions, uncovering possible connections between the physics inside and outside the horizon. We focus on the case of spacelike singularities in Einstein-scalar theory which are of the Kasner form. We find that the Kasner exponents are continuous and non-differentiable during the second order phase transitions, while discontinuous in the first order phase transitions. We give some arguments on the universality of this behavior. We also discuss possible observables in the dual field theory which encode the Kasner exponents.

Investigation of Phase Transitions in the Site-Diluted Three-Dimensional Potts Model

2012 ◽  
Vol 190 ◽  
pp. 687-690
Author(s):  
A.K. Murtazaev ◽  
A.B. Babaev
Keyword(s):  
Phase Transitions ◽  
Potts Model ◽  
Three Dimensional ◽  
Finite Size ◽  
Correlation Radius ◽  
Second Order ◽  
First Order ◽  
Nonmagnetic Impurities ◽  
Wolff Algorithm ◽  
First Order Phase

The phase transitions and critical phenomena in three-dimensional (3D) site-diluted 3-and 4-state Potts models is investigated by Monte-Carlo method based on the highly efficient Wolff algorithm. The systems with linear sizesL=20-44 at spin concentrationsp=1.00, 0.95, 0.90, 0.80, 0.70, 0.65 are explored. The second-order phase transition is shown to occur in the three-dimensional 3-state Potts model with nonmagnetic impurities. In the 4-state Potts model there are observed first-order phase transitions in weakly diluted state, when the model is strongly diluted the first-order phase transitions change to the second-order one. On the basis of the finite-size scaling theory static critical exponents of specific heatα, susceptibilityγ, magnetizationβ, and exponent of correlation radiusνfor the systems under study are calculated.

Trimodal-random field Blume-Capel model

2021 ◽  
pp. 2150270
Author(s):  
Erhan Albayrak
Keyword(s):  
Magnetic Field ◽  
Phase Transitions ◽  
Random Field ◽  
Phase Diagrams ◽  
Critical Points ◽  
Bethe Lattice ◽  
Recursion Relations ◽  
First Order ◽  
Random Magnetic Field ◽  
First Order Phase

The external random magnetic field [Formula: see text] with three nodes, i.e. acting up and down along the [Formula: see text]-axis and zero, effective on the spins in the Blume-Capel model is analyzed on the Bethe lattice in terms of the exact recursion relations. All the nodes are assumed to have the same probability, [Formula: see text], so that the model could give various kinds of phase transitions. As a mapping of the phase transitions, the phase diagrams are constructed on two different planes which present very rich and interesting phase diagrams. In addition to the second- and first-order phase transitions, a few critical points, reentrant and double reentrant behaviors are also observed.

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