Large exchange bias in Cr substituted Fe3O4 nanoparticles with FeO subdomains

Claudiu Bulbucan; Calle Preger; Aram Kostanyan; Kirsten M Ø Jensen; Esko Kokkonen; Cinthia Piamonteze; Maria E Messing; Rasmus Westerström

doi:10.1039/d1nr04614d

Large exchange bias in Cr substituted Fe₃O₄ nanoparticles with FeO subdomains

Nanoscale. 2021 Oct 1;13(37):15844-15852. doi: 10.1039/d1nr04614d.

Authors

Claudiu Bulbucan^{1

2}, Calle Preger^{1

3}, Aram Kostanyan^{4

5}, Kirsten M Ø Jensen⁶, Esko Kokkonen⁷, Cinthia Piamonteze⁵, Maria E Messing^{1

2

3}, Rasmus Westerström^{1

2}

Affiliations

¹ NanoLund, Lund University, Box 118, 22100 Lund, Sweden.
² Synchrotron radiation research, Lund University, SE-22100 Lund, Sweden. claudiu.bulbucan@sljus.lu.se.
³ Solid State Physics, Lund University, Box 118, 22100 Lund, Sweden.
⁴ Physik-Institut, Universität Zürich, CH-8057 Zürich, Switzerland.
⁵ Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
⁶ Department of Chemistry, University of Copenhagen, Copenhagen, Denmark.
⁷ MAX IV Laboratory, Lund University, PO Box 118, 221 00, Lund, Sweden.

Abstract

Tuning the anisotropy through exchange bias in bimagnetic nanoparticles is an active research strategy for enhancing and tailoring the magnetic properties for a wide range of applications. Here we present a structural and magnetic characterization of unique FeCr-oxide nanoparticles generated from seed material with a Fe : Cr ratio of 4.71 : 1 using a physical aerosol method based on spark ablation. The nanoparticles have a novel bimagnetic structure composed of a 40 nm ferrimagnetic Cr-substituted Fe₃O₄ structure with 4 nm antiferromagnetic Fe_xO subdomains. Cooling in an applied magnetic field across the Néel temperature of the Fe_xO subdomains results in a significant shift in the hysteresis, demonstrating the presence of a large exchange bias. The observed shift of μ₀H_E = 460 mT is among the largest values reported for Fe_xO-Fe₃O₄-based nanoparticles and is attributed to the large antiferromagnetic-ferrimagnetic interface area provided by the subdomains.