scholarly journals Reorientation phase transitions in thin magnetic films: a review of the classical vector spin model within the mean-field approach

2001 ◽  
Vol 81 (6) ◽  
pp. 613-628
Author(s):  
L. Udvardi, L. Szunyogh, A. Vernes, P.
Author(s):  
Nguyễn Từ Niệm ◽  
Bach Thanh Cong

This work studies on thermodynamic properties of ultra-thin magnetic films within the framework of a transverse Ising model. The equations for free energy, entropy and specific heat of spin system are obtained by using the mean field approximation. We also analyze the effect of the next nearest neighbor interaction on the critical temperature, the layer magnetization and the specific heat of thin films.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Angelika Abramiuk-Szurlej ◽  
Arkadiusz Lipiecki ◽  
Jakub Pawłowski ◽  
Katarzyna Sznajd-Weron

AbstractWe study the binary q-voter model with generalized anticonformity on random Erdős–Rényi graphs. In such a model, two types of social responses, conformity and anticonformity, occur with complementary probabilities and the size of the source of influence $$q_c$$ q c in case of conformity is independent from the size of the source of influence $$q_a$$ q a in case of anticonformity. For $$q_c=q_a=q$$ q c = q a = q the model reduces to the original q-voter model with anticonformity. Previously, such a generalized model was studied only on the complete graph, which corresponds to the mean-field approach. It was shown that it can display discontinuous phase transitions for $$q_c \ge q_a + \Delta q$$ q c ≥ q a + Δ q , where $$\Delta q=4$$ Δ q = 4 for $$q_a \le 3$$ q a ≤ 3 and $$\Delta q=3$$ Δ q = 3 for $$q_a>3$$ q a > 3 . In this paper, we pose the question if discontinuous phase transitions survive on random graphs with an average node degree $$\langle k\rangle \le 150$$ ⟨ k ⟩ ≤ 150 observed empirically in social networks. Using the pair approximation, as well as Monte Carlo simulations, we show that discontinuous phase transitions indeed can survive, even for relatively small values of $$\langle k\rangle$$ ⟨ k ⟩ . Moreover, we show that for $$q_a < q_c - 1$$ q a < q c - 1 pair approximation results overlap the Monte Carlo ones. On the other hand, for $$q_a \ge q_c - 1$$ q a ≥ q c - 1 pair approximation gives qualitatively wrong results indicating discontinuous phase transitions neither observed in the simulations nor within the mean-field approach. Finally, we report an intriguing result showing that the difference between the spinodals obtained within the pair approximation and the mean-field approach follows a power law with respect to $$\langle k\rangle$$ ⟨ k ⟩ , as long as the pair approximation indicates correctly the type of the phase transition.


1990 ◽  
Vol 05 (17) ◽  
pp. 3391-3399 ◽  
Author(s):  
AMRUTA MISHRA ◽  
H. MISHRA ◽  
S.P. MISRA

We discuss here some nonperturbative techniques of field theory, where we dress nuclear matter as a whole with off-mass-shell pions. Here s-wave pion pairs simulate the effect of σ-meson of the mean field approach of Walecka. The signatures are in agreement with earlier results along with new physical insight.


2016 ◽  
Vol 52 (2) ◽  
pp. 178-199 ◽  
Author(s):  
F. Baccelli ◽  
A. N. Rybko ◽  
S. B. Shlosman

2017 ◽  
Vol 28 (11) ◽  
pp. 1750133 ◽  
Author(s):  
Krzysztof Kułakowski ◽  
Piotr Gronek ◽  
Alfio Borzì

Recently, a computational model has been proposed of the social integration, as described in sociological terms by Blau. In this model, actors praise or critique each other, and these actions influence their social status and raise negative or positive emotions. The role of a self-deprecating strategy of actors with high social status has also been discussed there. Here, we develop a mean field approach, where the active and passive roles (praising and being praised, etc.) are decoupled. The phase transition from friendly to hostile emotions has been reproduced, similarly to the previously applied purely computational approach. For both phases, we investigate the time dependence of the distribution of social status. There we observe a diffusive spread, which — after some transient time — appears to be limited from below or from above, depending on the phase. As a consequence, the mean status flows.


1987 ◽  
Vol 01 (03n04) ◽  
pp. 997-1000 ◽  
Author(s):  
M.P. Das ◽  
A.G. Saif

We present a phenomenological approach in terms of two coexisting macroscopic order parameters correponding to the superconducting and the insulating states relevant to the high. temperature superconducting ceramics. On using the mean field approach we discuss the electrodynamical responses and from the fluctuations of the order parameters we obtain results for the electrical conductivity, which is shown to possess anomalies as in the granular materials.


2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Hadey K. Mohamad

The magnetic properties of a ferrimagnetic mixed spin-3/2 and spin-5/2 Ising model with different anisotropies are investigated by using the mean-field approximation (MFA). In particular, the effect of magnetic anisotropies on the compensation phenomenon, acting on A-atoms and B-ones for the mixed-spin model, has been considered in a zero field. The free energy of a mixed-spin Ising ferrimagnetic system from MFA of the Hamiltonian is calculated. By minimizing the free energy, we obtain the equilibrium magnetizations and the compensation points. The phase diagram of the system in the anisotropy dependence of transition temperature has been discussed as well. Our results of this model predict the existence of many (two or three) compensation points in the ordered system on a simple cubic lattice.


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