Open Access Nano Express

Field Dependence of the Spin Relaxation Within a Film of Iron Oxide Nanocrystals Formed via Electrophoretic Deposition

DW Kavich13, SA Hasan23, SV Mahajan23, J-H Park4 and JH Dickerson13*

Author Affiliations

1 Department of Physics and Astronomy, Vanderbilt University, Nashville, TN, 37235, USA

2 Interdisciplinary Graduate Program in Materials Science, Vanderbilt University, Nashville, TN, 37235, USA

3 Vanderbilt Institute for Nanoscale Science and Engineering, Vanderbilt University, Nashville, TN, 37235, USA

4 National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA

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Nanoscale Research Letters 2010, 5:1540-1545  doi:10.1007/s11671-010-9674-2

Published: 20 June 2010

Abstract

The thermal relaxation of macrospins in a strongly interacting thin film of spinel-phase iron oxide nanocrystals (NCs) is probed by vibrating sample magnetometry (VSM). Thin films are fabricated by depositing FeO/Fe3O4 core–shell NCs by electrophoretic deposition (EPD), followed by sintering at 400°C. Sintering transforms the core–shell structure to a uniform spinel phase, which effectively increases the magnetic moment per NC. Atomic force microscopy (AFM) confirms a large packing density and a reduced inter-particle separation in comparison with colloidal assemblies. At an applied field of 25 Oe, the superparamagnetic blocking temperature is TBSP ≈ 348 K, which is much larger than the Néel-Brown approximation of TBSP ≈ 210 K. The enhanced value of TBSP is attributed to strong dipole–dipole interactions and local exchange coupling between NCs. The field dependence of the blocking temperature, TBSP(H), is characterized by a monotonically decreasing function, which is in agreement with recent theoretical models of interacting macrospins.

Keywords:
Electrophoretic deposition; Core–shell; Superparamagnetic; EPD; Iron oxide; Thin film