Study of Magneto-viscosity of Ferromagnetic
Ferrofluid
G. Thirupathi and R. Singh*
School of Physics, University of Hyderabad, Central University P.O., Hyderabad-500046, India
Corresponding author’s e-mail: rssp@uohyd.ernet.in, Tel.: +91-40-23134321; Fax: +91-40-23010227
*
Abstract
Oleic acid coated Mn0.75Zn0.25Fe2O4 (MZF) nanoparticles
were dispersed in toluene for synthesis of ferromagnetic
ferrofluid. Shear rate (𝜸̇ ) vs. viscosity (η) plots at various
magnetic fields (H) show power law behavior with power
index (n) between 0.1 and 0.038. Herschel-Bulkley (H-B)
model fits for zero field shear stress (τ) vs. 𝜸̇ . The nonNewtonian behavior of the fluid is observed with
increasing shear thinning.
followed by its saturation at higher fields, with low
hysteresis when the applied field is decreased to zero.
This behavior is analogous to magnetic hysteresis loop
of the nanoparticles.
Keywords: Magneto rheology, ferrofluids, magneticnanoparticles.
Introduction
Ferromagnetic ferrofluids are exotic and useful
in a wide range of applications from computer disk
drives to rotary vacuum seals and speaker-damping
technology [1-2]. The colloidal suspension of
ferromagnetic nanoparticles gives high viscosity at low
applied magnetic field. High surface energy and
magnetic interactions between particles can lead to
formation
of
agglomerates
of
ferromagnetic
nanoparticles in the fluid. The stabilization of particle
size in ferrofluid can be done by using surfactant coated
particles dispersed in low viscosity fluids as colloidal.
Fig. 1: (a) XRD pattern and (b) TEM micrograph of
MZF nanoparticles respectively.
Synthesis
Oleic acid coated MZF nanoparticles were
synthesized
by
coprecipitation
method.
The
nanoparticles were dispersed in toluene as colloidal for
the synthesis of ferrofluid. The respective volume ratio
of MZF nanoparticles, oleic acid and toluene was taken
as 1:0.5:1.5.
Results and discussions
Fig 1 shows x-ray diffraction pattern and
Transmission electron microscope (TEM) micrograph
confirming the nanophase of the MZF nanoparticles.
The particle size distribution obtained from TEM
micrographs is 7 to 15 nm. The η vs. 𝛾̇ plots at various
fields show power law behavior with increase in shear
thinning with magnetic field. The zero filed τ vs. 𝛾̇ plot
shows H-B fluid behavior with n-value of 0.25 and yield
stress of 0.37Pa [3]. Since the ferromagnetic particles
are dispersed in less viscous fluid (toluene with
viscosity of 0.52mPas), the magneto viscosity plots
show a rapid increase with increase in magnetic field
Fig. 2: (a) η vs. 𝛾̇ at 0, 0.06, 0.99 and 1.33T field values
(inset zero field τ vs. 𝛾̇ , H-B model fit), and (b)
magneto-viscosity plot of MZF ferrofluid respectively.
Acknowledgment
G. T is grateful for BSR fellowship from UGC.
References
[1] Noel a. Clark, “Ferromagnetic ferrofluids”, Nature,
504 (2013), pp. 229-230.
[2] G. Thirupathi and R. Singh, “Magneto-viscosity of
MnZn-ferrite ferrofluid”, Physica B, (2014) in press.
[3] R.Y. Hong, Z.Q. Rena, Y.P. Han, H.Z. Li, Y.
Zheng and J. Ding“Rheological properties ofwaterbased Fe3O4ferrofluids”, Chem. Engg. Sci. 62 (2007),
pp. 5912 – 5924.