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Controlling the exchange bias field in Co core/CoO shell nanoparticles Mikhail Feygenson,1 Yuen Yiu,1 Angela Kou,1 Ki-Sub Kim,2 and Meigan C. Aronson1,3,*
 

Summary: Controlling the exchange bias field in Co core/CoO shell nanoparticles
Mikhail Feygenson,1 Yuen Yiu,1 Angela Kou,1 Ki-Sub Kim,2 and Meigan C. Aronson1,3,*
1Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
2Department of Chemical and Biological Engineering, Chungju National University, 72 Daehak-ro, Chungju, Chungbuk
380-702, Korea
3Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
Received 19 February 2010; revised manuscript received 16 April 2010; published 28 May 2010
We have determined how the anomalous exchange bias effect in Co/CoO nanoparticles of 11 nm in diameter
depends on the Co core and CoO shell dimensions. The oxidation of the Co nanoparticles used in this study is
carefully controlled, yielding highly crystalline and oriented interfaces. The dimensions of the core and shell
are determined from magnetization and small angle x-ray scattering measurements. The exchange bias field in
Co/CoO core-shell nanoparticles depends nonmonotonically on the CoO shell thickness, reaching a maximum
value of 7 kOe at 30 K when the core and shell dimensions are similar. We propose that lattice strain induces
a net moment at the core-shell interface, and it is the variation of this moment with strain, which is responsible
for the vanishing of HEB at both large and small Co shell thicknesses.
DOI: 10.1103/PhysRevB.81.195445 PACS number s : 81.07. b, 73.22.Dj, 75.60. d
I. INTRODUCTION
The exchange bias effect occurs when a ferromagnet
FM in direct contact with an antiferromagnet AFM is
cooled below the Néel temperature of the latter in an applied

  

Source: Aronson, Meigan - Department of Physics and Astronomy, SUNY at Stony Brook

 

Collections: Materials Science; Physics