Monodisperse FePt Nanoparticles and Ferromagnetic FePt Nanocrystal Superlattices

Sun, Shouheng; Murray, C. B.; Weller, D.; Folks, L.; Möser, Andreas

doi:10.1126/science.287.5460.1989

Cited by 6,024 publications

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“…The results are applicable for many emerging materials, including artificially self-assembled nanoparticle arrays and a certain class of manganites, where localization effects within the clusters can be neglected. Arrays of ferromagnetic nanoparticles are becoming one of the mainstreams of current mesoscopic physics [1,2,3,4]. Not only ferromagnetic granules promise to serve as logical units and memory storage elements meeting elevated needs of emerging technologies, but also offer an exemplary model system for investigation of disordered magnets.…”

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confidence: 99%

“…The tunneling conductance is the main parameter that controls macroscopic transport properties of the sample [15]. In consideration of applications to experiments [1,3,13,16] we restrict ourselves to the case where the tunneling conductance is smaller than the quantum conductance [17]. In the SPM state the charge degrees are coupled with the spin degrees of freedom; to reflect this connection, the tunneling conductance can be written in a form g t (θ) = g 0 t (1 + Π 2 cos θ), [18], where g 0 t is the tunneling conductance in the paramagnetic state [19]…”

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Electron Transport in Nanogranular Ferromagnets

2007

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We study electronic transport properties of ferromagnetic nanoparticle arrays and nanodomain materials near the Curie temperature in the limit of weak coupling between the grains. We calculate the conductivity in the Ohmic and non-Ohmic regimes and estimate the magnetoresistance jump in the resistivity at the transition temperature. The results are applicable for many emerging materials, including artificially self-assembled nanoparticle arrays and a certain class of manganites, where localization effects within the clusters can be neglected.PACS numbers: 73.43.Qt Arrays of ferromagnetic nanoparticles are becoming one of the mainstreams of current mesoscopic physics [1,2,3,4]. Not only ferromagnetic granules promise to serve as logical units and memory storage elements meeting elevated needs of emerging technologies, but also offer an exemplary model system for investigation of disordered magnets. At the same time the model of weakly coupled nanoscale ferromagnetic grains proved to be useful for understanding the transport properties of doped manganite systems [5,6] that have intrinsic inhomogeneities. Recent studies showed that above the Curie temperature these materials possess a nanoscale ferromagnetic cluster structure which to a large extend controls transport in these systems [7,8,9,10]. This defines an urgent quest for understanding and quantitative description of electronic transport in ferromagnetic nanodomain materials based on the model of nanogranular ferromagnets.In this paper we investigate electronic transport properties of arrays of ferromagnetic grains [11] near the ferromagnetic-paramagnetic transition, see Fig. 1. At low temperatures, T < T s c , the sample is in a so called superferromagnetic (SFM) state, see Fig. 1, set up by dipole-dipole interactions. Near the macroscopic Curie temperature, T s c , thermal fluctuations destroy the macroscopic ferromagnetic order. At intermediate temperatures T s c < T < T g c , where T g c is the Curie temperature of a single grain, the system is in a superparamagnetic (SPM) state where each grain has its own magnetic moment while the global ferromagnetic order is absent. At even higher temperatures, T > T g c , the ferromagnetic state within each grain is destroyed and the complete sample is in a paramagnetic state. We consider the model of weakly interacting grains in which the sample Curie temperature is much smaller than the Curie temperature of a single grain, T s c ≪ T g c . We first focus on the SPM state, and discuss a d−dimensional array (d = 3, 2) of ferromagnetic grains taking into account Coulomb interactions between electrons. Granularity introduces additional energy parameters apart from the two Curie temperatures, T g c and T s c : each nanoscale cluster is characterized by (i) the charging c , where T s c is the macroscopic Curie temperature of the system, the ferromagnetic grains (superspins) form a superferromagnet (SFM); for T s c < T < T g c , where T g c is the Curie temperature for a single grain, the system is in a superparamagne...

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Electron Transport in Nanogranular Ferromagnets

2007

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“…Welldefined two-dimensional lattices of magnetic dots have been successfully prepared by using chemical techniques (colloids) [12,13]. The structure of these lattices could be changed from square to hexagonal by changing the nature of the ligand.…”

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Preparation of nanometer-scale iron dots on insulating layer

Ernult

Mitani

Nagano

et al. 2003

Science and Technology of Advanced Materials

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“…For ammonia-alcoholic solutions concentration is 0. 16,17 . The solutions were prepared by weight method using chemically pure chemicals.…”

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Direct Laser Synthesis of Ag Nanoparticles from Ammonia-alcoholic Solutions of AgNO3

Михайлов¹,

Evich²,

A³

2016

ACSi

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Ag nanoparticles were synthesized as a result of irradiation of ammonia-alcoholic solution of AgNO 3 with focused beam of Nd:YAG laser. The synthesized nanoparticles were characterized with SEM and EDX analysis, dynamic light scattering technique, absorption and luminescence spectroscopies. The average size of synthesized nanoparticles which is from 25 to 100 nm demonstrates a linear dependence on molar concentration of the used solution. Optical and luminescence properties of obtained Ag nanoparticles were demonstrated.

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Monodisperse FePt Nanoparticles and Ferromagnetic FePt Nanocrystal Superlattices

Cited by 6,024 publications

References 23 publications

Electron Transport in Nanogranular Ferromagnets

Electron Transport in Nanogranular Ferromagnets

Preparation of nanometer-scale iron dots on insulating layer

Direct Laser Synthesis of Ag Nanoparticles from Ammonia-alcoholic Solutions of AgNO3

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