Iron Oxide-based Magnetic Nanoparticles for High Temperature Span Magnetocaloric Applications
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Iron Oxide-based Magnetic Nanoparticles for High Temperature Span Magnetocaloric Applications V. Chaudhary1,2,3 and R. V. Ramanujan3# 1
Interdisciplinary Graduate School, Nanyang Technological University, Singapore, 639798 Energy Research Institute @NTU (ERI@N), Nanyang Technological University, Singapore 637553 3 School of Materials Science and Engineering, Nanyang Technological University, Singapore, 639798 # Corresponding author: [email protected] 2
ABSTRACT The magnetocaloric effect of chemically synthesized Mn0.3Zn0.7Fe2O4 superparamagnetic nanoparticles with average crystallite size of 11 nm is reported. The magnitude of the magnetic entropy change (ΔSM), calculated from magnetization isotherms in the temperature range of 30 K to 400 K, increases from - 0.16 J-kg-1K-1 for a field of 1 T to - 0.88 J-kg-1K-1 for 5 T at room temperature. Our results indicate that ΔSM values are much higher than primarily reported values for this class of nanoparticles. ΔSM is not limited to the ferromagnetic-paramagnetic transition temperature; instead, it occurs over a broad range of temperatures, resulting in high relative cooling power. INTRODUCTION Room temperature magnetic refrigeration, based on the magnetocaloric effect (MCE), has significant advantages compared to the conventional gas-compression cooling technique, e.g., no greenhouse gases as well as high energy efficiency.1,2 It is apparent from Figure 1 that the search for new materials with large MCE has gained significant momentum in the last decade. In addition, it can also be seen (inset of Figure 1) that recently researchers are focusing on magnetocaloric materials for room temperature applications. Gadolinium and other rare earth based alloys have been intensively studied but they are expensive, available in limited quantities and corrode easily.1,3,4 Magnetocaloric nanoparticles (MCNPs) have attracted considerable interest because they can exhibit superior properties compared to bulk materials. When the particle size and domain size (~10-15 nm) are similar, the magnetic behavior can be superparamagnetic or spin glass at room temperature.5,6 Superparamagnetic particles possess large moment, high saturation magnetization and a non-hysteretic M-H curve with zero remanence and coercivity. When the particle size of LaXCa1-XMnO3 decreased from 43 nm to 17 nm, the first order transition that induces a narrow temperature interval of the magnetic entropy change can be converted to a second order transition with a broad change in entropy.7 In another study, Co-and Mg-ferrite nanoparticles also exhibited a wide change in entropy accompanying a second order phase transitions.5,8 The main advantage of such nanoparticles is a broad working temperature range, which increases the relative cooling power (RCP).
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