Nano Today (2009) 4, 438447

avai lab le at www.sc iencedi rec t .com

journa l homepage: www.e lsev ier .com/ locate /nanotoday

REVIEW

Nano

Georgi

a Departme Statb Institute o

Received 8 3 AuAvailable on

KEYWOSuperparamagnetism;Finite-size effects;Surface eIntrinsicstructureExchangeMonte Casimulatio

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enced by surface and nite-size effects. Theories of dynamic spin uctuation and spin reversalprocesses for uniaxial, isolated magnetic nanoparticles are presented, as applied primarily to

Introduct

Materials ebased apprwith novelresources oexplosionrecent advcesses andallow the mof matter aentic discrecent advnetism hold

Correspoversity, MendStates. Tel.:

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1748-0132/$doi:10.1016/ffects;spin;-bias;rlons

the interpretation of magnetization and Mssbauer spectroscopic measurements. Monte Carlosimulation studies that corroborate experimental ndings and advance elucidation of core vs.surface contributions to magnetic behavior are also presented. In addition, applications tonano and bio technology and future research directions in core/shell, matrix embedded andinteracting magnetic nanoparticles are also addressed. 2009 Published by Elsevier Ltd.

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ngineering utilizes an interdisciplinary, science-oach to the production of nanophase materialsmicrostructure, in order to tap the physicalf the quantum/classical boundary. The presentin nanoscale research derives primarily fromances in synthetic approaches, biomimetic pro-the development of enabling technologies thatanipulation, stabilization and characterizationt the atomic level. Among the fundamental sci-iplines that have contributed to extraordinaryances in nanoscience and nanotechnology, mag-s a prominent place. Finite-size effects in the

ndence address: Department of Physics, Villanova Uni-el Hall, 800 Lancaster Ave., Villanova, PA 19073, United+1 610 519 4883.dress: gcp@villanova.edu.

magnetic properties of matter have unraveled interestingnew magnetic phenomena in nano-materials, not mani-fested in the bulk [1,2]. This has led to new physics and newtechnological applications in diverse areas of science andtechnology ranging from ultra-high density magnetic record-ing [35], improved nanocomposite permanent magnetmaterials [6], giant-magneto-resistance phenomena [7,8],spintronics [9,10], biogenic nano-magnets [11,12] to fastexpanding bio-medical applications [1316]. The discoveryof giant magneto-resistance earned the 2007 Nobel Prizein Physics due to its important device applications in newread-head technologies [17]. Thus, magnetism, arguably theoldest scientic discipline to have been continuously inves-tigated since the mining of magnetite (loadstone) in ancientGreece in the 6th century BC, still offers fertile ground forscientic innovation today, within the realm of nanomag-netism.

In this article the fundamental physics that governnanoparticle magnetism is reviewed as garnered from exper-imental and theoretical studies of the magnetic properties

see front matter 2009 Published by Elsevier Ltd.j.nantod.2009.08.006particle magnetism

a C. Papaefthymioua,b,

nt of Physics, Villanova University, Villanova, PA 19073, Unitedf Materials Science, NCSR Demokritos, 15310 Athens, Greece

July 2009; received in revised form 11 August 2009; accepted 1line 11 September 2009

RDS Summary The current status of funis reviewed. Emphasis is placed on stes

gust 2009

ental physics that govern nanoparticle magnetisms of the particles intrinsic spin structure as inu-

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Nanoparticle magnetism 439

of nanoparticles pertained to their intrinsic spin structureand spin dynamical phenomena unique to the nanostruc-tured state. In addition, applications to nano and biotechnology and future research directions in core/shell,matrix embedded and interacting magnetic nanoparticlesare briey

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The magneto its respothe applicmaterialsrespectiveeld. To titive magneld, givintechnologiorder in minter-atomcouples nesion princiexchangecan be deHamiltonia

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