AVS 51st International Symposium
    Magnetic Interfaces and Nanostructures Wednesday Sessions
       Session MI-WeA

Invited Paper MI-WeA5
Overcoming Thermal Fluctuations in Ferromagnetic Nanostructures using Exchange Bias

Wednesday, November 17, 2004, 3:20 pm, Room 304A

Session: Exchange Coupling, Surfaces, and Interfaces
Presenter: J. Nogués, Inst. Catalana de Recerca i Estudis Avancats, Spain
Authors: J. Nogués, Inst. Catalana de Recerca i Estudis Avancats, Spain
V. Skumryev, Inst. Catalana de Recerca i Estudis Avancats, Spain
S. Stoyanov, U. of Delaware
Y. Zhang, U. of Delaware
G. Hadjipanayis, U. of Delaware
D. Givord, CNRS-Grenoble, France
K. Liu, U. of California-Davis
C. Leighton, U. of Minnesota
H. Masuda, Tokyo Metro. U., Japan
K. Nishio, Tokyo Metro. U., Japan
I.V. Roshchin, UCSD
I.K. Schuller, UCSD
J. Eisenmenger, U. Ulm, Germany
J. Sort, U. Autònoma de Barcelona, Spain
J.S. Muñoz, U. Autònoma de Barcelona, Spain
S. Suriñach, U. Autònoma de Barcelona, Spain
M.D. Baró, U. Autònoma de Barcelona, Spain
Correspondent: Click to Email
Today's interest in nanoparticle magnetism is stimulated by a variety of potential applications, ranging from ultra-high density information storage to medicine. Most applications rely on the magnetic order of the nanoparticles being stable with time. However, in small particles, thermal fluctuations may affect the magnetization stability and possibly lead to superparamagnetism. In this study, we will demonstrate that the exchange coupling between ferromagnetic (FM) nanostructures and antiferromagnetic (AFM) hosts can lead to the magnetic stabilization, i.e. enhancement of coercivity (H@sub C@), increase of remanence (M@sub R@) and ultimately improvement of the superparamagnetic blocking temperature (T@sub B@). Three different cases will be discussed: (i) Co particles ball milled with NiO@footnote 1@, where a small increase of the coercivity and the remanence is observed. (ii) Fe nanostructures deposited on FeF@sub 2@ layers@footnote 2@, where a clear enhancement of the remanence of the hysteresis loop is seen and appears to be linked with its coercivity enhancement. (iii) Co nanoparticles embedded in CoO@footnote 3@, where the blocking temperature is substantially improved with the concomitant increase of H@sub C@ and M@sub R@. In particular, 4nm-Co particles, embedded in a CoO matrix, remain ferromagnetic up to the Néel temperature of CoO. This corresponds to almost 30-fold increase in the blocking temperature compared to the uncoupled nanoparticles. The AFM-FM coupling can be viewed as providing an extra source of anisotropy, thus leading to magnetization stability. @FootnoteText@ @footnote *@ Work supported by EU, CICYT and DGR (UAB), NSF, Seagate (UDEL) and US-DOE (UCSD)@footnote 1@ J. Sort et al., Appl. Phys Lett. 75, 3177 (1999)@footnote 2@ K. Liu et al., Appl. Phys Lett. 81, 4434 (2002)@footnote 3@ V. Skumryev et al. Nature 423, 850 (2003).