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Tunneling and charging effects in discontinuous superparamagnetic Ni81Fe19/Al2O3 multilayers
Uppsala University.
Chalmers University of Technology, Göteborg.
Chalmers University of Technology, Göteborg.
Uppsala University.
Vise andre og tillknytning
2010 (engelsk)Inngår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 81, nr 22, s. 224437-Artikkel i tidsskrift (Annet vitenskapelig) Published
Abstract [en]

The magnetic and transport properties of films based on discontinuous layers of Ni81Fe19 (Py) embedded inAl2O3 were investigated. In films with nominal Py thicknesses 6 and 8 Å superparamagnetic particles withmedian diameters Dmed=2.8 and 3.1 nm and distribution widths s_D=1.2 and 1.3 nm were formed. Current-voltage (IU) curves were measured with the current perpendicular to the film plane. The analyses show that thecharge transport occurs via tunneling; with the charging energy supplied by thermal fluctuations at hightemperature, T>100 K, and by the electric field at low temperature, T<10 K. The separation of the tworegimes allows independent estimates of the mean charging energy <EC>~40 meV for both samples; from theresistance R versus T analyzed in an effective-medium model at high temperature and from I versus U at 4 K.In order to obtain a consistent description of the transport properties, the size distributions must be included toaccount for the deviation from the single size behavior R~exp(EC/kBT) at high T. The scaling parameter inthe relation I \propto (U/Uth−1)^g, where Uth is the threshold for conduction, is estimated to g~2 at 4 K. The superparamagneticrelaxation of the particles becomes blocked below a temperature T~20 K respective 30 K for 6and 8 Å. The magnetic field (B) dependence of the resistance R(B) displays a single maximum of the ratio MR=[R(B)−R(2 T)] /R(2 T) in zero field at room temperature and a characteristic splitting of the peak at 4K, attributed to the blocking. The maxima, ~0.9% for 6 Å and 1.1% for 8 Å, are positioned at fields abouta factor of two to three higher than the coercive fields of the samples

sted, utgiver, år, opplag, sider
American Physical Society , 2010. Vol. 81, nr 22, s. 224437-
Emneord [en]
Giant magnetoresistance, Electrical conduction, Room temperature, Transport properties, Granular films, Metal-films, Magnetization, Superlattices, Particles, Junctions
HSV kategori
Identifikatorer
URN: urn:nbn:se:hj:diva-12684DOI: 10.1103/PhysRevB.81.224437OAI: oai:DiVA.org:hj-12684DiVA, id: diva2:326764
Tilgjengelig fra: 2010-06-24 Laget: 2010-06-24 Sist oppdatert: 2017-12-12bibliografisk kontrollert

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