Induced ferro-ferromagnetic exchange bias in nanocrystalline systems

Martínez-García, J.C.; Rivas, M.; Garcı́a, Javier

doi:10.1016/j.jmmm.2014.10.123

Cited by 8 publications

(4 citation statements)

References 32 publications

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“…The hysteresis curve for nanocrystallized soft magnetic systems was extracted from the intrinsic switching field distribution of the sample, as it is simulated with a combination of a Gaussian distributions [16], that has an intersection of ideas with [11]; other approach is based on the solid base of Landau-Lifshitz-Gilbert equations [17].…”

Section: General Remarksmentioning

confidence: 99%

Magnetoelectric effects theory by Heisenberg method based on permutation group symmetry of nanoparticles

Leble¹

2020

Nanosystems: Phys. Chem. Math.

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The Heisenberg theory of ferromagnetism is widened to include external electric field action. The material relations are derived by means of differentiation of logarithm of partition function with respect to the magnetic and electric fields. The mean energy coefficients as the exchange integrals combinations are expressed via characters of irreducible representations of corresponding permutation groups by the Heitler method. The thermodynamic equations of state for polarization and magnetization, as functions of the electric and magnetic fields, are derived and illustrated by figures. The magnetization and hysteresis curves in magnetization -magnetic field components plane are built. The theory is applied to nanoparticles, the particle partition function is modeled as the product of the surface and bulk parts. The statistical sum is constructed having explicit expressions for the mean energy in terms of exchange integrals and number of closest neighbors for surface and bulk atoms. The relative contribution of the surface and bulk terms is evaluated.

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Section: General Remarksmentioning

confidence: 99%

Magnetoelectric effects theory by Heisenberg method based on permutation group symmetry of nanoparticles

Leble¹

2020

Nanosystems: Phys. Chem. Math.

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“…In this framework, it is appealing to combine materials whose properties can be individually tuned to create a magnetic system where enhanced "non-exchange" bias might develop 30 . Although a number of both experimental and theoretical efforts in this direction have been reported in recent years, the elucidation of the nature of diverse effects, particularly those resulting from interparticle dipolar interactions, is lacking for binary hybrid systems, where the intrinsic properties of the constituents conceal any collective effects [31][32][33][34] . In this context, engineering homogeneous binary dense assemblies of highly uniform nanoparticles offers a simple and controlled scenario to explore different parameters in the resulting loop shifts 35 .…”

Section: Introductionmentioning

confidence: 99%

Non-Exchange Bias in Soft-Hard Nanoparticle Composites

Maltoni,

López-Martín,

Sánchez

et al. 2024

Preprint

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Exchange bias has been extensively studied both in exchange-coupled thin films and nanoparticle composite systems. However, the role of non-exchange mechanisms in the overall hysteresis loop bias are far from being understood. Here, dense soft-hard binary nanoparticle composites are used as a novel tool not only to unravel the effect of dipolar interactions on the hysteresis loop shift, but as a new strategy to enhance the bias of any magnet exhibiting an asymmetric magnetization reversal. Mixtures of equally sized, 6.8 nm, soft γ-Fe2O3 nanoparticles (no bias – symmetric reversal) and hard cobalt doped γ-Fe2O3 nanoparticles (large exchange bias – asymmetric reversal) reveal that, for certain fractions of soft particles, the loop shift of the composite can be significantly larger than the exchange-bias field of the hard particles in the mixture. Simple calculations indicate how this emerging phenomenon can be further enhanced by optimizing the parameters of the hard particles (coercivity and loop asymmetry). In addition, the existence of a dipolar-induced loop shift (“dipolar bias”) is demonstrated both experimentally and theoretically, where, for example, a bias is induced in the initially unbiased γ-Fe2O3 nanoparticles due to the dipolar interaction with the exchange-biased hard nanoparticles. These results open a new paradigm in the large field of hysteresis bias and pave the way for novel approaches to tune loop shifts in magnetic hybrid systems beyond interface exchange coupling.

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“…The microscopic Heisenberg model goes to the macroscopic Landau-Lifshits-Gilbert (LLG) equations as it is explained in [19,20]. For example, in the article [21] a ferromagnetic alloy explore such LLG-based model for a hysteresis loop building with 3D LLG equations. Further, magnetic bi-phase nanocrystalline systems with biased (non-symmetric) hysteresis loops are presented in [22], where micromagnetic computations of magnetostatic and exchange interactions have been made within the model using Euler-Lagrange equations for classic Lagrangean.…”

Section: Introductionmentioning

confidence: 99%

Ferromagnetic Hysteresis by Heisenberg Partition Function and Its Processing Methods in Nanoparticle Magnetization Modeling

Chychkalo¹,

Leble²

2021

Preprint

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The Heisenberg {\it ab initio} theory of magnetization is developed to apply for multilayer nanoparticles. The theory is based on distribution and partition functions modification with account the difference between exchange integral and closest neighbour numbers, that change the system of resulting transcendental equation for magnetization and its reversal to form either a paramagnetic type curve or hysteresis loops patterns. The equations are obtained within the Heisenberg partition function construction by Heitler diagonalization of energy matrix via irreducible representations of permutation symmetry group. A combination with the Gauss distribution gives the explicit expression for the partition function in the asymptotic limit] at large spin range in terms of transcendent function. The exchange integral, as a parameter of the equation of state (material equation) is evaluated from Curie temperature value by means of a formula derived within the presented theory. Methods of data processing from the simultaneous solution of the material equation system are proposed. The multi-valued function of hysteresis loop is found by combination of graphical approach and special procedure for elimination of mistaken peaks and prolapses of the patterns. The theory and computation methods are applied to spherical particles with separate surface layers consideration. The contribution of the surface layers, that are specified by number of closest neighbors and exchange integrals into overall magnetization, is studied for two-layer and three-layer models, that are discussed and compared graphically.

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Induced ferro-ferromagnetic exchange bias in nanocrystalline systems

Cited by 8 publications

References 32 publications

Magnetoelectric effects theory by Heisenberg method based on permutation group symmetry of nanoparticles

Magnetoelectric effects theory by Heisenberg method based on permutation group symmetry of nanoparticles

Non-Exchange Bias in Soft-Hard Nanoparticle Composites

Ferromagnetic Hysteresis by Heisenberg Partition Function and Its Processing Methods in Nanoparticle Magnetization Modeling

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