Abstract
Dynamical effects under geometrical frustration are considered in a model for artificial spin ice on a square lattice in two dimensions. Each island of the spin ice has a three-component Heisenberg-like dipole moment subject to shape anisotropies that influence its direction. The model has real dynamics, including rotation of the magnetic degrees of freedom, going beyond the Ising-type models of spin ice. The dynamics is studied using a Langevin equation solved via a second-order Heun algorithm. Thermodynamic properties such as the specific heat are presented for different couplings. A peak in specific heat is related to a type of melting-like phase transition present in the model. Hysteresis in an applied magnetic field is calculated for model parameters where the system is able to reach thermodynamic equilibrium.
Highlights
We found that the specific heat and average separation between monopoles with opposite charges exhibit a sharp peak and a local maximum, respectively, at the same temperature [22], Tp ≈ 7.2D/kB, where D is the strength of the dipolar interactions and kB is Boltzmann’s constant
Our results indicate that systems exhibiting real dynamics are feasible, in such a way that their ground states could be achieved
We have studied the possibilities of spin dynamics in frustrated artificial spin-ice systems consisting of two-dimensional square lattices of elongated magnetic nanoislands
Summary
Departamento de Fısica, ICEx, Universidade Federal de Minas Gerais, 31270-901 Belo Horizonte, MG, Brazil. 4 Author to whom any correspondence should be addressed. Using an Ising model for the magnetic moments of the nanoislands, thermal effects in artificial square ice were studied recently by some of us [22] with Monte Carlo simulation. Using a Langevin dynamics approach we have studied different models for possible artificial square spin ices. For ordinary realizations with Py islands the system is not thermally driven to its ground state, indicating a possible dynamical bottleneck, absent in systems with real dynamics. Three models (denoted by A, B and C) with different lattice and island parameters are studied to see the possibility of thermalized spin ice dynamics.
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