Thermo-magnetic properties of ternary polydispersed Mn0.5Zn0.5Fe2O4 ferrite magnetic fluid

• Ternary Mn0.5Zn0.5Fe2O4 ferrite magnetic fluid of 6 nm size is synthesized using chemical route.
• Particles are superparamagnetic with 374 K TC and 2.1 emu/cc K (dM/dT)fluid.
• Thermal conductivity of nanofluid shows 45% enhancement at 10% volume fraction.
• Thermal conductivity is insensitive to transverse magnetic field.
• 4% Enhancement with temperature rise makes the system a better choice for heat transfer devices.

Thermo-magnetic properties of ternary Mn0.5Zn0.5Fe2O4 ferrite magnetic fluid is investigated using a SQUID magnetometer and thermal conductivity analyzer. Crystallite size of the particles is obtained as 5.95 nm with size distribution of 0.23. M–T measurement of fluid shows that the system is highly temperature sensitive with the pyromagnetic co-efficient of the fluid as 2.1 emu/cc K. The Curie temperature of the material was estimated using the Bloch theory, which is 374 K. Thermal conductivity of nanofluid shows 45% enhancement for 10% volume fraction at 25 °C temperature. The increment in thermal conductivity is linear with increase in volume fraction but significantly higher than the predicted Maxwell׳s theory, Maxwell-Garnett and Bruggeman theory. Even though the nanofluid is highly sensitive to magnetic field the application of transverse magnetic field does not show any further enhancement in thermal conductivity. These results are explained considering the dipolar coupling co-efficient which in the present system is lower than unity and hence does not favor the long chain like structures. The temperature dependent thermal conductivity shows enhancement of 4% in the temperature range of 25–65 °C which makes it an attractive choice for heat transfer devices.