2 research outputs found
Structure and magnetic properties of Fe nanoparticles embedded in a Cr matrix
The structure of 2 nm diameter (340 atoms) Fe nanoparticles embedded in a Cr matrix was determined using X-ray Absorption Fine Structure (EXAFS) and the magnetic properties studied by Superconducting Quantum Interference Device (SQUID) magnetometry. The thin films were produced by the co-deposition of pre-formed gas-phase Fe clusters synthesised by a gas aggregation source with an atomic vapour of Cr produced by an MBE source. The behaviour was studied as a function of Fe nanoparticle volume fraction in the range 5-20% and was compared to previous results on ferromagnetic nanoparticles in antiferromagnetic matrices. EXAFS showed that the atomic structure in the Cr-embedded Fe nanoparticles is the same as the bulk bcc structure. Whereas alloying between the nanoparticles and matrix material has previously been shown to be very pronounced for Co nanoparticles in antiferromagnetic Mn, it was found that any alloying between Fe nanoparticles and Cr matrix material is limited. For dilute samples of Fe nanoparticles in Cr the measured saturation magnetisation (M) was 1μ/Fe atom, which is significantly less than the bulk M value of 2.22μ/Fe atom indicating that the surface of Fe nanoparticles is either antiferromagnetic or non-magnetic. An increase in the volume fraction produces an increase in the value of M and at a volume fraction of 20%, M exceeds the value of bulk Fe showing that some Cr spins provide a ferromagnetic contribution. After field cooling below 30 K, all films show Exchange Bias (EB) and an increase of coercivity, which are both much larger for the most concentrated sample. The Cr spins at the surface of the Fe particles play a key role in determining the overall magnetic behaviour
Magnetic anisotropy and superspin glass behaviour of Fe nanoparticles embedded in Cr and Ag matrices
Static and dynamical magnetic
properties of
Fe
nanoparticles
(NPs)
embedded
in non
-
magnetic
(Ag) and antiferromagnetic (Cr) matrices
with a volume filling fraction
(VFF)
of 10%
have been
investigated
. In both
Fe@Ag and Fe@Cr nanocomposites
, the Fe nanoparticles have a narrow size
distribution, with
a
mean particle diameter
around
2 nm. In both
samples
, the saturation
magnetization reaches that of
Fe
bulk bcc, suggesting
the absence
of
alloying
with the matrices.
The
coercivity
at 5 K
is
much larger in Fe@Cr
than in Fe@Ag
as a result of
the
strong interaction
between
the
Fe NPs and
the
Cr matrix. Temperature
-
dependent magnetization and ac
-
susceptibility
measurements
point out
further
evidence
of
the
enhanced
inter
-
particle interaction in
the
Fe@Cr
system
. While
the
behavior
of Fe@Ag
indicates the presence of weakly interacting magnetic
monodomain particles
with a wide distribution of
blocking temperatures
, Fe@Cr
behaves like a
superspin glass
produced
by the
magnetic
interaction
between
nanoparticles