Ferromagnetic Resonance and Magneto-transport
Behavior Correlation via Interparticle Interactions in
Cu100–xCox Nanogranular Films
Dinesh Kumar*, Sujeet Chaudhary, and Dinesh K. Pandya
Thin Film Laboratory, Physics Department, Indian Institute of Technology Delhi, New Delhi 110016, India.
*Corresponding author, e-mail:dinesh1.goyal@gmail.com, Tel.:+911126586521
Abstract
Increasing demagnetizing field and anisotropic response of
the magnetoresistance with the increase of ‘x’ in Cu100-xCox
films indicate the presence of interparticle interactions. The
correlation between magnetoresistance and ferromagnetic
resonance is established by interpreting the interparticle
interactions in terms of resonance field and line width of the
ferromagnetic resonance spectra.
Keywords: Nanogranular, Superparamagnetic, Ferromagnetic
resonance, Magnetoresistance, Interactions.
Introduction
Nanogranular magnetic systems have been
widely studied, yet the degree of correlation between
the magnetoresistance (MR) response and the associated
changes in the overall magnetic states continues to be
one of the challenges in understanding these systems.
Independently, magnetoresistance [1-2], magnetization
[3], and ferromagnetic resonance (FMR) [4] studies are
reported on the magnetic properties of these films. Few
of them [4-5] are trying to interpret the FMR spectra
with percentage MR, but no efforts are made to correlate
the evolution of MR behavior with FMR spectra. In this
work, the correlation between the two independent
measurements of MR and FMR have been attempted on
100 nm thick sputtered Cu100-xCox (x=17.8-33.3 at%)
films. The interparticle interactions probing ability of
FMR is presented to understand the MR behavior of
Cu100-xCox films.
Results
The MR and FMR spectra are recorded at room
temperature with magnetic field (H) parallel (H||) and
perpendicular (H) to the sample plane. It is found that
for x≤20.9 films MR is isotropic and Co particles
present are of superparamagnetic nature. Evolution of
perpendicular demagnetizing field and in plane
anisotropy as a function of ‘x’ indicates the presence of
ferromagnetic and superparamagnetic particles in
x>20.9 films. This finding is interpreted in terms of
particle size and interparticle interactions. Fig. 1(a)
shows the resonance field (Hr) determined from FMR
spectra. Hr is moving towards low (high) H for field
parallel (perpendicular) to film plane and the difference
of resonance field ∆Hr increases monotonically with the
increase of ‘x’, evidenced the presence of interparticle
interactions and established the role of increased
interactions for the observed MR behavior. The increase
in line width (∆H) with the increase of ‘x’ (fig 1(b))
depicts the increase of particle size and further
confirmed the role of interparticle interactions for the
detected MR behavior.
Fig. 1: Dependence of (a) resonance field (Hr) and the
difference of resonance filed (∆Hr) (b) line width (∆H)
on ‘x’ in H|| and H┴ geometries.
Acknowledgment
One of the authors D.K. acknowledges
MHRD-Government of India for the SRF Fellowship.
References
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