Role of positional disorder in fully textured ensembles of Ising-like dipoles

Abstract

We study by numerical simulation the magnetic order in ensembles of randomly packed magnetic spherical particles which, induced by their uniaxial anisotropy in the strong coupling limit, behave as Ising dipoles. We explore the role of the frozen disorder in the positions of the particles assuming a common fixed direction for the easy axes of all spheres. We look at two types of spatially disordered configurations. In the first one we consider isotropic positional distributions which can be obtained from the liquid state of the hard sphere fluid. We derive the phase diagram in the $T$-$\Phi$ plane where $T$ is the temperature and $\Phi$ the volume fraction. This diagram exhibits long-range ferromagnetic order at low $T$ for volume fractions above the threshold ${\Phi }_c=0.157$ predicted by mean-field calculations. For $\Phi \lesssim {\Phi }_c$ a spin-glass phase forms with the same marginal behavior found for other strongly disordered dipolar systems. The second type of spatial configurations we study are anisotropic distributions that can be obtained by freezing a dipolar hard sphere liquid in its polarized state at low temperature. This structural anisotropy enhances the ferromagnetic order present in isotropic hard sphere configurations.

arXiv comment10 pages, 13 figures

References in corpus (22)

• Exchange Monte Carlo Method and Application to Spin Glass Simulations
• Simulated Tempering: A New Monte Carlo Scheme
• Jammed Hard-Particle Packings: From Kepler to Bernal and Beyond
• Packing Hyperspheres in High-Dimensional Euclidean Spaces
• Universal Finite Size Scaling Functions in the 3D Ising Spin Glass
• Estimate of the Cutoff Errors in the Ewald Summation for Dipolar Systems
• Magnetic nanoparticles: from the nanostructure to the physical properties
• Ordering of dipolar Ising crystals
• Orientational Ordering in Spatially Disordered Dipolar Systems
• Spin Glass Transition at Nonzero Temperature in a Disordered Dipolar Ising System: The Case of LiHoxY{1-x}F4
• Ferroelectric and Dipolar Glass Phases of Non-Crystalline Systems
• Quantification of dipolar interactions in Fe${}_{3-x}$O${}_4$ nanoparticles
• Monte Carlo study of the spin-glass phase of the site-diluted dipolar Ising model
• Crossover From Individual to Collective Magnetism in Dense Nanoparticle Systems: Local Anisotropy Versus Dipolar Interactions
• Effects of setting the temperatures in the parallel tempering Monte Carlo algorithm
• Dynamic Correlation Length Growth in Superspin Glass: Bridging Experiments and Simulations
• Phase diagram of a three-dimensional dipolar model on a FCC lattice
• Phase diagram for ensembles of random close packed Ising-like dipoles as a function of texturation
• Nature of the spin-glass phase in dense packings of Ising dipoles with random anisotropy axes
• Phase diagram of a three-dimensional dipolar Ising model with textured Ising axes
• Magnetic ordering of random dense packings of freely rotating dipoles
• Ferromagnetic frozen structures from the dipolar hard spheres fluid at moderate and small volume fractions