Dipolar ferromagnetic order in a cubic system

Rošer, Miran; Corruccini, L. R.

doi:10.1103/physrevlett.65.1064

Cited by 46 publications

(30 citation statements)

References 21 publications

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“…Compared to the fcc case, the M-H loop for the sc lattice has a shallower slope of the magnetization's field dependence and a larger field is required to reach saturation. These differences are an indication of the tendency towards ferromagnetic order between dipoles on a fcc lattice (without boundaries) [3][4][5] in contrast to the sc lattice which tends toward antiferromagnetic order. Indeed, the results of this finite-size simulation show a remanent spin configuration that is similar to the 90 0 domain structure expected of a ferromagnetic cube in the fcc case.…”

Section: Zero Temperature Resultsmentioning

confidence: 99%

Micromagnetic simulations of interacting dipoles on an fcc lattice: application to nanoparticle assemblies

Plumer

Lierop

Southern

et al. 2010

J. Phys.: Condens. Matter

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Micromagnetic simulations are used to examine the effects of cubic and axial anisotropy, magnetostatic interactions and temperature on M-H loops for a collection of magnetic dipoles on fcc and sc lattices. We employ a simple model of interacting dipoles that represent single-domain particles in an attempt to explain recent experimental data on ordered arrays of magnetoferritin nanoparticles that demonstrate the crucial role of interactions between particles in a fcc lattice. Significant agreement between the simulation and experimental results is achieved, and the impact of intra-particle degrees of freedom and surface effects on thermal fluctuations are investigated

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Section: Zero Temperature Resultsmentioning

confidence: 99%

Micromagnetic simulations of interacting dipoles on an fcc lattice: application to nanoparticle assemblies

Plumer

Lierop

Southern

et al. 2010

J. Phys.: Condens. Matter

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“…In such a case, an understanding of ObD at T = 0 + can not be leveraged to explain the selection at T c . Examples include the transition to long-range order in the pyrochlore Heisenberg antiferromagnet with indirect DM interactions [50,65,66], the problem of magnetization direction selection in face-centered cubic dipolar ferromagnets [67,68] and the topical issue of state selection in XY pyrochlore antiferromagnets [45,49,64,[69][70][71][72][73]. …”

Section: A) B)mentioning

confidence: 99%

Fluctuation-Driven Selection at Criticality in a Frustrated Magnetic System: The Case of Multiple-kPartial Order on the Pyrochlore Lattice

et al. 2015

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We study the problem of partially ordered phases with periodically arranged disordered (paramagnetic) sites on the pyrochlore lattice, a network of corner-sharing tetrahedra. The periodicity of these phases is characterized by one or more wave vectors k = { 1 2 1 2 1 2 }. Starting from a general microscopic Hamiltonian including anisotropic nearest-neighbor exchange, long-range dipolar interactions and second-and third-nearest neighbor exchange, we identify using standard mean-field theory (s-MFT) an extended range of interaction parameters that support partially ordered phases. We demonstrate that thermal fluctuations ignored in s-MFT are responsible for the selection of one particular partially ordered phase, e.g. the "4-k" phase over the "1-k" phase. We suggest that the transition into the 4-k phase is continuous with its critical properties controlled by the cubic fixed point of a Ginzburg-Landau theory with a 4-component vector order-parameter. By combining an extension of the Thouless-Anderson-Palmer method originally used to study fluctuations in spin glasses with parallel-tempering Monte-Carlo simulations, we establish the phase diagram for different types of partially ordered phases. Our results elucidate the long-standing puzzle concerning the origin of the 4-k partially ordered phase observed in the Gd2Ti2O7 dipolar pyrochlore antiferromagnet below its paramagnetic phase transition temperature. Highly frustrated magnetism is one of the paradigms of modern condensed matter physics [1]. In frustrated magnets, the combination of lattice geometry and competing interactions often leads to degenerate classical states. The degeneracies are generally accidental as they are not protected by the symmetries of the spin Hamiltonian. Yet, the degenerate states may be related by transformations that form an emergent symmetry group. Near a continuous phase transition, these approximate symmetries provide "organizing principles" in determining the critical properties by distinguishing relevant perturbations from irrelevant ones. In the most interesting case, the leading degeneracy-lifting perturbations, which may be relevant or irrelevant in the renormalization group sense, are thermal or quantum fluctuations -a phenomenon called order-by-disorder (ObD) [2][3][4][5]. The competition among diverse degeneracy-lifting effects can result in a modulated long-range ordered state at nonzero wave vector k, which may or may not be commensurate with the lattice [6][7][8][9][10][11][12]. In some cases, a number of superposed symmetryrelated k modes within the first Brillouin zone form a socalled multiple-k order [6,7,13,14]. A particular interesting form of such modulated magnetism is a partially ordered state (POS) with periodically arranged "paramagnetic" sites [15][16][17][18]. These fluctuating magnetic moments decimate a fraction of the energy-costly frustrated bonds while retaining an extensive entropy, hence lowering the free energy.In this Letter, we study the convergence of the aforementioned phenomena (emergent symmet...

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“…Dipolar ferromagnetism is distinguished from the common ferromagnetic order due to exchange interactions. Experimental evidence for this state was first obtained in rare-earth salts, with a dipolar Curie temperature T c,dip of ϳ0.1 K. 2 Later calculations 3,4 suggested the feasibility of the dipolar ferromagnetic state at higher temperatures for dense assemblies of monodomain magnetic nanoparticles. Magnetic force microscopy 5 and x-ray photoemission electron microscopy 6 have provided experimental evidence of dipolar ferromagnetic ordering in nanoparticle assemblies.…”

mentioning

confidence: 99%

Dipolar ferromagnetic phase transition in Fe3O4 nanoparticle arrays observed by Lorentz microscopy and electron holography

Yamamoto

Hogg

Yamamuro

et al. 2011

Applied Physics Letters

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Dipolar ferromagnetism formed in Fe 3 O 4 nanoparticle arrays is revealed by Fresnel Lorentz microscopy and electron holography. Dipolar domain walls do not lie preferentially along macrograin boundaries but depend on the overall shape of the assembly, meaning magnetostatic energy dominates. The domain structures are imaged at different temperatures for both monolayer and bilayer arrays. The domain wall contrast in the monolayer region is visible until 575°C, and the magnetic order parameter steeply drops toward the temperature. In the bilayer region, finer and more complicated domains are formed. © 2011 American Institute of Physics. ͓doi:10.1063/1.3556562͔ Dipolar ferromagnetism was theoretically predicted by Luttinger and Tisza, 1 who showed that a face-centered-cubic lattice of point dipoles has a ferromagnetic ground state. Dipolar ferromagnetism is distinguished from the common ferromagnetic order due to exchange interactions. Experimental evidence for this state was first obtained in rare-earth salts, with a dipolar Curie temperature T c,dip of ϳ0.1 K. 2Later calculations 3,4 suggested the feasibility of the dipolar ferromagnetic state at higher temperatures for dense assemblies of monodomain magnetic nanoparticles. Magnetic force microscopy 5 and x-ray photoemission electron microscopy 6 have provided experimental evidence of dipolar ferromagnetic ordering in nanoparticle assemblies. Electron holography 7,8 ͑EH͒ revealed the existence of vortexlike magnetic domains in monolayers of 8 nm -Co nanoparticles with a 4.2 nm edge-to-edge separation. The domains were stable over at least 1 h at 108 K. However, questions remain about the nature of the magnetic ordered state. In this paper we use transmission electron microscopy ͑TEM͒ to image the structural arrangement of Fe 3 O 4 nanoparticles, and Fresnel Lorentz microscopy ͑FLM͒ and EH to image their magnetization patterns at different temperatures. We show that the overall shape of the assembly, rather than the macrograin boundaries of the nanoparticle arrays, dominates the magnetization pattern. Temperature-dependent magnetic imaging from 24 to 605°C shows the evolution of these magnetostatic domains and provides direct evidence of a dipolar ferromagnetic phase transition.Magnetic nanoparticles of Fe 3 O 4 were synthesized by decomposition of iron acteylacetonate in oleic acid and oleylamine surfactants. 9 The nanoparticles of 13.4Ϯ 1.5 nm diameter were used to form a Langmuir layer on immiscible liquid using a minitrough. After allowing the oleic acid to evaporate, the nanoparticles were compressed to obtain close-packed monolayers, and then transferred to carboncoated TEM grids by the Langmuir-Schaefer method. Figures 1͑a͒ and 1͑b͒ show the low magnification TEM image of the array and the higher magnification image in the array region, respectively.10 Small black dots in the array in Fig. 1͑a͒ were areas with particle agglomerates. The particles were separated by the surfactant, with an edge-to-edge separation of 1.6Ϯ 0.6 nm, and had random crystallograph...

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Dipolar ferromagnetic order in a cubic system

Cited by 46 publications

References 21 publications

Micromagnetic simulations of interacting dipoles on an fcc lattice: application to nanoparticle assemblies

Micromagnetic simulations of interacting dipoles on an fcc lattice: application to nanoparticle assemblies

Fluctuation-Driven Selection at Criticality in a Frustrated Magnetic System: The Case of Multiple-kPartial Order on the Pyrochlore Lattice

Dipolar ferromagnetic phase transition in Fe3O4 nanoparticle arrays observed by Lorentz microscopy and electron holography

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