A Study of 2d Ising Ferromagnets With Dipole Interactions

Abstract

A two-dimensional Ising model with competing short range ferromagnetic and long range dipolar interactions is used to study the transition properties and phase diagram in ultrathin magnetic films. Monte Carlo simulations in systems with exchange and dipolar interactions reveal a ground state of striped phases with varying width. By raising the temperature, the domain walls are smeared out by fluctuations, leading to a random domain mesoscopic phase with no long-range order, and finally the domains are melted to the high-temperature disordered phase. Local magnetic field distributions and specific heat calculations reproduced transition points consistent with the previous phase diagram of the model. The resemblance to the phase diagram in ultrathin magnetic films, such as in Fe/Cu(100), is discussed.

Effect of Size, Temperature, and Structure on the Vibrational Heat Capacity of Small Neutral Gold Clusters

“…Of course, there is an increasing amount literature illustrating the conceptual and practical relevance of two dimensional (2D) systems with long range interactions [69][70][71]. The vibrational frequency of FCs contributions comes from both the symmetric and the asymmetric stretch and bending modes.…”

Monte Carlo study of the honeycomb structure of anthraquinone molecules on Cu(111)

“…They can be a 2D dipolar lattice gas, 15 a 2D dipolar Ising model without vacancies [16][17][18][19][20][21] and with random vacancies, 22 a 2D frustrated system, 23 a bidimensional fluid system, 24 a 2D quantum Heisenberg model, 25 a density anomaly, 26 a spin-glass state, 27 correlations in fluids, 28 compositional patterns on bulk-immiscible alloy films, 29 and a colloidal fluid. 30 Our work is also based on this method.…”

“…The positive coupling constant A gives the strength of the long-range |R| −3 dipolar interactions due to electrostatic and elastic repulsions. [15][16][17][18][19][20][21] The ′ in the second sum means that i = j term is excluded, and ij[k] in the first term can be three-or more-site interactions 31,32 as well as pairwise interactions.…”

Metric features of a dipolar model

“…It has been supposed that one or more transitions could take place in the region between the ordered and paramagnetic phases. In particular, Ifti and coworkers [2] studied by numerical Monte Carlo (MC) simulations the behavior of specific heat, obtaining a curve with a sharp peak at temperature T 1 and a broad maximum in the region at T 2 ∼ 2T 1 . The authors suggested the existence of two possible phase transitions, the former related to the melting of the stripes, the latter to the occurrence of the paramagnetic phase.…”

“…In addition, for PFD, a careful examination of clusters proves to be useful in recovering, along new and more efficient lines, previously introduced parameters and criteria [1] [2]. Notations, definitions and elementary properties of C(M) and Z(M), as well as Shannon entropy, Hamming and Rohlin distances, are recalled in the Appendix, with some mathematical details.…”