SCientifiC REPORtS | (2018) 8:3425 | DOI:10.1038/s41598-018-21626-0
Spin canting across core/shell
Samuel D. Oberdick
, Ahmed Abdelgawad
, Carlos Moya
, Samaneh Mesbahi-Vasey
, Vlado K. Lazarov
, Richard F. L. Evans
, Daniel Meilak
, Johan van Lierop
, Ian Hunt-Isaak
, Hillary Pan
, Yumi Ijiri
, Kathryn L.
, Julie A. Borchers
& Sara A. Majetich
Magnetic nanoparticles (MNPs) have become increasingly important in biomedical applications like
magnetic imaging and hyperthermia based cancer treatment. Understanding their magnetic spin
congurations is important for optimizing these applications. The measured magnetization of MNPs
can be signicantly lower than bulk counterparts, often due to canted spins. This has previously been
presumed to be a surface eect, where reduced exchange allows spins closest to the nanoparticle
surface to deviate locally from collinear structures. We demonstrate that intraparticle eects can induce
spin canting throughout a MNP via the Dzyaloshinskii-Moriya interaction (DMI). We study ~7.4 nm
diameter, core/shell Fe
MNPs with a 0.5 nm Mn-ferrite shell. Mössbauer spectroscopy,
x-ray absorption spectroscopy and x-ray magnetic circular dichroism are used to determine chemical
structure of core and shell. Polarized small angle neutron scattering shows parallel and perpendicular
magnetic correlations, suggesting multiparticle coherent spin canting in an applied eld. Atomistic
simulations reveal the underlying mechanism of the observed spin canting. These show that strong DMI
can lead to magnetic frustration within the shell and cause canting of the net particle moment. These
results illuminate how core/shell nanoparticle systems can be engineered for spin canting across the
whole of the particle, rather than solely at the surface.
Single domain, magnetic nanoparticles (NPs) have been widely investigated for applications in materials science
. Most research on nanoparticles has largely focused on how size, shape, structure and chemi-
cal composition aect magnetic properties
. e past decade has seen major advances in terms of sub-nanometer
probes of materials and fabrication techniques, which have allowed exploration of magnetic eects due to a
non-uniform spin conguration within a nanoparticle
. Core/shell nanoparticles with hard/so magnetic lay-
ers can be synthesized with high structural precision for engineered magnetic interactions between the layers
Controlled magnetic interactions between core/shell layers have been used to tailor the magnetic response of
and for enhanced heat generation for magnetic hyperthermia
. Particular attention has
been paid to Fe
/Mn-ferrite core/shell structures with strong exchange coupling in nanoparticle systems
Spin canting at high elds was rst proposed to explain a reduced moment in Mn ferrite found by both neu-
tron diraction and Mössbauer spectroscopy
, and later supported by high eld dierential susceptibility
measurements. Since then numerous studies of ferrite NPs have identied a separate
component in Mössbauer spectra attributed to canted spins
, or to disordered surface spins
. Small angle
neutron scattering demonstrated spin canting that was coherent within a surface shell for Fe
; this has
been conrmed by a combination of high resolution electron energy loss spectroscopy (HREELS) and density
functional theory (DFT) calculations
Physics Department, Carnegie Mellon University, Pittsburgh, PA, 15213, USA.
Applied Physics Division, Physical
Measurement Laboratory, NIST, Boulder, CO, 80305, USA.
Materials Science and Engineering Department,
Carnegie Mellon University, Pittsburgh, PA, 15213, USA.
Chemistry Department, Carnegie Mellon University,
Pittsburgh, PA, 15213, USA.
SuperSTEM, Sci-Tech Daresbury Campus, Daresbury, WA4 4AD, UK.
of Physics, University of York, Heslington, York, YO10 5DD, UK.
The York-JEOL Nanocentre, York Science Park,
Heslington, York, YO10 5BR, UK.
Physics and Astronomy Department, University of Manitoba, Winnipeg, MB R3T
Physics and Astronomy Department, Oberlin College, Oberlin, OH, 44074, USA.
NIST Center for
Neutron Research, NIST, Gaithersburg, Maryland, 20899, USA. Correspondence and requests for materials should
be addressed to S.A.M. (email: email@example.com)
Received: 8 November 2017
Accepted: 7 February 2018
Published: xx xx xxxx