Easy axis distribution in interacting fine-particle systems

Rodríguez, Iglesias; Rubio, H.; Suárez, S.

doi:10.1063/1.122496

Cited by 11 publications

(3 citation statements)

References 7 publications

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“…Thanks to recent advances of numerical calculations, realistic multiparticle systems could be reliably simulated using Monte-Carlo techniques where the exact dipolar Hamiltonian is explicitly taken into account [66][67][68][69][70][71]. Most of the simulations and the experimental results agree that the magnetostatic interaction results in an increase of T B -with a noticeable exception [61] -and a slower decay of the remanence and of the coercivity with increasing temperature.…”

Section: Random 3d Systemsmentioning

confidence: 86%

Magnetic Ordering due to Dipolar Interaction in Low Dimensional Materials

Panissod

Drillon

2001

Magnetism: Molecules to Materials IV

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In the quest towards the development of new materials, in which the dimensions of the building units do not exceed a few atoms in at least one direction of the spaceorganic magnets built of spin chains or lamellae, for instance, or magnetic dots, wires and multilayers -the scientists are currently facing the influence of through-space interactions of dipolar origin. Basically, the concept of dipolar interaction is very familiar in solid state physics, and its manifestations at the macroscopic scale are well described in many textbooks [1], and actually used for magnetic applications. However, at the atomic scale, this interaction is mostly negligible and, when it occurs, the magnetic ordering is controlled by the quantum exchange mechanism which usually prevails in 3D networks.In this chapter, we demonstrate that the dipole-dipole interaction may have a foremost importance when considering low dimensional magnetic materials, made of strongly correlated objects of dimensionality zero (0D), one (1D) or two (2D) interacting through a weak interaction of dipolar origin. The aim is not to provide an exhaustive review on the dipolar interaction effects in magnetic materials but rather an outlook, both theoretical and experimental, on the magnetic ordering of 0D to 2D units embedded in higher dimensionality systems.From a fundamental viewpoint, magnetic ordering due to pure dipole-dipole interaction is a clean phase transition problem since the related Hamiltonian does not involve any adjustable parameter: unlike the exchange-coupled systems, one cannot change the form and the magnitude of the interaction in order to improve the agreement between theory and experiment. Therefore, experimental observations provide a direct answer for testing the models used to predict the magnetic structure and the ordering temperature, if observed.From the applied physics viewpoint, the pure dipole-dipole interaction is essentially an academic problem as long as only ionic/atomic moments are involved. Indeed the expected dipolar ordering temperature is of the order of µM s /k B (M s is the saturation magnetization and µ the individual moment) that is at most a few Kelvin for rare earth compounds. Nevertheless, there is nowadays a large renaissance of interest for pure dipole systems that involve not individual atomic moments but magnetic assemblies comprising a large number of strongly exchange coupled atomic moments. Indeed the magnetic ordering temperature for such systems can be much higher than in classical dipole systems because the magnetic moment µ of the objects Magnetism: Molecules to Materials IV. Edited by Joel S. Miller and Marc Drillon

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Section: Random 3d Systemsmentioning

confidence: 86%

Magnetic Ordering due to Dipolar Interaction in Low Dimensional Materials

Panissod

Drillon

2001

Magnetism: Molecules to Materials IV

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“…A large number of experimental papers containing a variety of results have been published in the last years. [7][8][9][10][11][12][13][14][15] Furthermore, computer simulations have extensively been used, leading to several contradictory conclusions, mainly dependent on the approach adopted to investigate the problem. Several recent works have found important deviations from the classical Langevin law in the case of pure superparamagnetic systems and usually attribute the deviations to the presence of strong anisotropies, also mentioning the possible existence of magnetic interactions.…”

Section: Introductionmentioning

confidence: 99%

Granular Cu-Co alloys as interacting superparamagnets

et al. 2001

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The anhysteretic magnetization of the granular metallic alloy Cu 90 Co 10 is experimentally studied over a wide temperature range ͑2-700 K͒. The measurements definitely exclude that this alloy is a simple superparamagnet, even in the high-temperature limit, although some features of granular systems ͓such as the typical Langevin-like form of the anhysteretic magnetization curves M (H)͔ are often taken as evidence of superparamagnetism. A phenomenological theory is proposed, explicitly considering that particle moments interact through long-ranged dipolar random forces, whose effect is pictured in terms of a temperature T*, adding to the actual temperature T in the denominator of the Langevin function argument. This simple formula explains all features of the experimental M (H) curves. The theory indicates that the actual magnetic moments on interacting Co particles are systematically larger than those obtained fitting the magnetic data to a conventional Langevin function. The Cu 90 Co 10 granular alloy is therefore identified as an ''interacting superparamagnet'' ISP. The ISP regime appears as separating the high-temperature, conventional superparamagnetic phase from the low-temperature, blocked-particle regime. In this way, a magnetic-regime diagram can be drawn for each granular system. The competition between single-particle and collective blocking mechanisms is briefly analyzed. The proposed interpretation is thought to be applicable to other fine particle systems; its main features and intrinsic limits are discussed.

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“…3,4,9,17,18 Only recently, with the enormous development of computers and important advances of the techniques of statistical physics, realistic multiparticle systems could be reliably simulated using Monte Carlo techniques. [19][20][21][22][23][24] In this case, there are many simulation models which make use of different approaches and approximations, and therefore the literature is full of inconclusive and/or conflicting results. However, recent investigations agree that magnetostatic interaction produces an increase in T B , in agreement with experimental findings 19,21 ͑with an important exception measured by Morup and Tronc 4 ͒.…”

Section: Introductionmentioning

confidence: 99%

Magnetic hysteresis based on dipolar interactions in granular magnetic systems

et al. 1999

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The magnetic hysteresis of granular magnetic systems is investigated in the high-temperature limit (Tӷ blocking temperature of magnetic nanoparticles͒. Measurements of magnetization curves have been performed at room temperature on various samples of granular bimetallic alloys of the family Cu 100Ϫx Co x (x ϭ5-20 at. %) obtained in ribbon form by planar flow casting in a controlled atmosphere, and submitted to different thermal treatments. The loop amplitude and shape, which are functions of sample composition and thermal history, are studied taking advantage of a novel method of graphical representation, particularly apt to emphasize the features of thin, elongated loops. The hysteresis is explained in terms of the effect of magnetic interactions of the dipolar type among magnetic-metal particles, acting to hinder the response of the system of moments to isothermal changes of the applied field. Such a property is accounted for in a mean-field scheme, by introducing a memory term in the argument of the Langevin function which describes the anhysteretic behavior of an assembly of noninteracting superparamagnetic particles. The rms field arising from the cumulative effect of dipolar interactions is linked by the theory to a measurable quantity, the reduced remanence of a major symmetric hysteresis loop. The theory's self-consistence and adequacy have been properly tested at room temperature on all examined systems. The agreement with experimental results is always striking, indicating that at high temperatures the magnetic hysteresis of granular systems is dominated by interparticle, rather than single-particle, effects. Dipolar interactions seem to fully determine the magnetic hysteresis in the high-temperature limit for low Co content (xр10). For higher concentrations of magnetic metal, the experimental results indicate that additional hysteretic mechanisms have to be introduced. ͓S0163-1829͑99͒01037-1͔

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Easy axis distribution in interacting fine-particle systems

Abstract: Negative remanent magnetization of fine particles with competing cubic and uniaxial anisotropies

Cited by 11 publications

References 7 publications

Magnetic Ordering due to Dipolar Interaction in Low Dimensional Materials

Magnetic Ordering due to Dipolar Interaction in Low Dimensional Materials

Granular Cu-Co alloys as interacting superparamagnets

Magnetic hysteresis based on dipolar interactions in granular magnetic systems

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