Renaud Patte

A phase field model for snow crystal growth in three dimensions

Snowflake growth provides a fascinating example of spontaneous pattern formation in nature. Attempts to understand this phenomenon have led to important insights in non-equilibrium dynamics observed in various active scientific fields, ranging from pattern formation in physical and chemical systems, to self-assembly problems in biology. Yet, very few models currently succeed in reproducing the diversity of snowflake forms in three dimensions, and the link between model parameters and thermodynamic quantities is not established. Here, we report a modified phase field model that describes the subtlety of the ice vapour phase transition, through anisotropic water molecules attachment and condensation, surface diffusion, and strong anisotropic surface tension, that guarantee the anisotropy, faceting and dendritic growth of snowflakes. We demonstrate that this model reproduces the growth dynamics of the most challenging morphologies of snowflakes from the Nakaya diagram. We find that the growth dynamics of snow crystals matches the selection theory, consistently with previous experimental observations.Spontaneous patterns: Simulating snowflakes with a softer touchA model that reproduces complex 3D snowflake growth using versatile interface descriptors may benefit other dendritic materials. Snow crystals solidify by expanding outward from an initial seed, capturing water molecules as they travel through the atmosphere. While most simulation methods treat this growing interface as a sharp boundary, Gilles Demange and colleagues from the University of Rouen in France report that a less rigid approach yields highly realistic results. Their technique uses a phase field model to represents the snowflake’s surface as a thin moveable layer where ice and vapour mix, and a new surface tension function to explain the anisotropic crystallisation. Including a special algorithm to simulate 3D crystal faceting enabled the model to duplicate essential snowflake morphologies and potentially predict ice water content in clouds under various weather conditions.

Magnetoelectric properties of multiferroic CuCrO2 studied by means of ab initio calculations and Monte Carlo simulations

Motivated by the discovery of multiferroicity in the geometrically frustrated triangular antiferromagnet CuCrO2 below its Neel temperature T-N, we investigate its magnetic and ferroelectric propert ...

Magnetisation switching in a ferromagnetic Heisenberg nanoparticle with uniaxial anisotropy: a Monte Carlo investigation

Abstract We investigate the thermal-activated magnetisation reversal in a single ferromagnetic nanoparticle with uniaxial anisotropy using Monte Carlo simulations. The aim of this work is to reproduce the reversal magnetisation by uniform rotation at very low temperature in the high-energy barrier hypothesis, that is to realize the Neel–Brown model. For this purpose we have considered a simple cubic nanoparticle where each site is occupied by a classical Heisenberg spin. The Hamiltonian is the sum of an exchange interaction term, a single-ion anisotropy term and a Zeeman interaction term. Our numerical data of the thermal variation of the switching field are compared to an approximated expression and previous experimental results on Co nanoparticles.

Phase-Field Modelling of Spinodal Decomposition during Ageing and Heating

Despite the tremendous success of phase-field (PF) modelling in predicting many of the experimentally observed microstructures in solids, additional progress is required in order to apply it to predict microstructure evolution in real alloy systems. One way to achieve this is to couple thermodynamic and kinetic databases with PF model. In this work, we present phase-field simulations of spinodal decomposition in Fe-Cr alloy during thermal ageing and anisothermal heating. In the PF method, the local free energy is directly constructed using the CALPHAD method. During isothermal ageing, the morphology of decomposed phases consisted in an interconnected irregular shape for short ageing times, and a further ageing caused the change to a droplet like shape of the decomposed Cr-rich phase. The influence of heating rate on phase transformations is then simulated and compared with experimental results obtained by differential thermal analysis, carried out with heating rates in the range 0.5 °C.min-1 to 15 °C.min-1. The simulation results show that heating rate strongly influences the microstructure morphology.

Magnetic properties of Fe/Dy multilayers: A Monte Carlo investigation

Abstract We investigate the magnetic properties of a Heisenberg ferrimagnetic multilayer by using Monte Carlo simulations. The aim of this work is to study the local structural anisotropy model which is a possible origin of the perpendicular magnetic anisotropy in transition metal/rare earth amorphous multilayers. We have considered a face centered cubic lattice where each site is occupied by a classical Heisenberg spin. We have introduced in our model of amorphous multilayers a small fraction of crystallised Fe–Dy nanoclusters with a mean anisotropy axis along the deposition direction. We show that a competition in the energy terms takes place between the mean uniaxial anisotropy of the Dy atoms in the nanoclusters and the random anisotropy of the Dy atoms in the matrix.