Phase diagram of a three-dimensional dipolar Ising model with textured Ising axes

Abstract

We study from tempered Monte Carlo simulations the magnetic phase diagram of a textured dipolar Ising model on a face centered cubic lattice. The Ising coupling of the model follow the dipoledipole interaction. The Ising axes are distributed with a uniaxial symmetry along theẑ direction with a gaussian probability density of the polar angles. This distribution provides a quenched disorder realization of the dipolar Ising model making a continuous link between the parallel axes dipoles and the random axes dipole models. As expected the phase diagram presents three distinctive phases: paramagnetic, ferromagnetic and spin-glass. A quasi long range ferromagnetic and a reentrant spin-glass phases are obtained in the vicinity of the ferromagnetic spin-glass line. This model provides a way to predict the magnetic phases of magnetic nanoparticles supracrystals in terms of the texturation of the easy axes distribution in the strong anisotropy limit. * n ∈ [0.55, 3.50] and an arithmetic distribution. * c , by using the finite size behavior of B q (L), q 2 and the probability distribution P (q) of the overlap order parameter. P (q) is characterized by two broad peaks located at

Enhanced structural and magnetic properties of fcc colloidal crystals of cobalt nanoparticles

“…10,14 The ZFC peak temperatures are thus assigned to the paramagnetic (PM)/SSG transition slightly smaller than T r = ( 0 /4k B )(/M s ) 2 d NC 3 (/ m ) as deduced from theoretical simulations. 15,16 A precise determination of the freezing temperature Tp is not possible due to the lack of a precise value of Ms ; however the upper bond, Tr, is in between 176K and 214 K for /m = 0.38 corresponding to the supercrystalline film with Ms in between 70 and 85 emu/g and d NC = 8.1 nm and respectively between 203 K and 247 K for d NC = 8.5 nm. We can corroborate our interpretation by noting that the supercrystalline film to the colloidal crystals Tp ratio follows the corresponding volume fractions ratio namely 0.81 versus 0.85 respectively where the volume fraction ratio is obtained from the ratio of the t-3 values.…”

“…13 Such a dipolar SFM state results necessarily from strong DDI and given the known properties of dipolar systems, it is expected to occur in assemblies of NCs provided they meet the following conditions: the NCs must be organized on either a well ordered supercrystal of face-centered cubic (fcc), hexagonal close packed (hcp), body centered tetragonal (bct) symmetry or a close packed structure (random close packed, RCP) on the one hand and characterized by either a very weak anisotropy or a strongly textured distribution of easy axes on the other hand. 8,[14][15][16] Single supercrystals (also called colloidal crystals) made of densely and regularly packed NCs constitute potential candidates for this aim. 8 Today, few examples of colloidal crystals have been reported in the literature.…”

Ferromagnetic frozen structures from the dipolar hard spheres fluid at moderate and small volume fractions

“…In order to thermalize in an efficient way our system presenting strongly frustrated states, we use parallel tempering algorithm 22 (also called tempered Monte Carlo) for our Monte Carlo simulations. Such a scheme is widely used in similar systems 17,18,23 , and we do not enter in the details. The method is based on the simultaneous simulation runs of identical replica for a set of temperatures {T * n } with exchange trials of the configurations pertaining to different temperatures each N M Metropolis steps according to an exchange rule satisfying the detailed balance condition.…”

“…0.42. This phase diagram for different situations of DHS frozen distributions 6,[17][18][19] with or without MAE has been revisited in more details recently. In each of the situations considered the structure is disordered and isotropic or ordered on a lattice with cubic symmetry and there is one disorder control parameter, say x.…”

Magnetic ordering of random dense packings of freely rotating dipoles

“…The role played by the degree of orientational disorder, called texturation, in the magnetic order has been studied by MC simulations both in FCC lattices and in RDP. [18][19][20] In particular, the phase diagram of nontextured FCC systems has been obtained as a function of E a /E dd , 21 where the ratio E a /E dd is an estimate the degree of disorder in such non-textured lattices.…”