Abstract
Fe–Co–Cr alloys have been developed with a Curie temperature, Tc, appropriate for ferrofluid cooling and self-regulated heating applications. These alloys have low Curie temperatures, moderate magnetic moments and provide increased heat capacity in a liquid used in a thermal cycle. Amorphous powders have been synthesized by cryo-SPEX milling melt-spun ribbons at 77 K. Transmission electron microscopy reveals cryomilled magnetic nanoparticles (MNPs) with a mean diameter of 4.2 nm to form agglomerates ∼30 nm in size. Vibrating sample magnetometer and superconducting quantum interference device magnetometry of amorphous powders reveal a specific magnetization, σs, of 104 emu/g at 4 K in a 300 mT field and a Tc of 335 K. Nanoparticles were suspended in ferrofluids by ultrasonication with a Pluronic F127 surfactant to stabilize them in aqueous solution. Ferrofluids of varying MNP concentration were rf heated in a 27.2 mT field at 267 kHz. For 1.24 vol % of MNPs in the ferrofluid, a solution reached temperatures>50 °C in ∼70 s, and showed Curie-limiting temperature behavior at ∼75 °C. These results demonstrate self-limited heating of FeCoCr MNPs at 75 °C which may have application in polymer curing.
Highlights
Applications of thermodynamics to heat engines, refrigerators, heat pumps, etc., rely on the efficient use of thermodynamic cycles
These same type of ferrofluids with appropriate Tc’s offer dual use application in the self-regulated heating of MNPsRef. 2͒ in temperature ranges of interest for applications of polymer curing3 and cancer thermotherapies.4. These alloys are interesting due to their low Tc, moderate magnetic moment, and increased heat capacity in a liquid used in a thermal cycle
Our research focuses on tuning Curie temperatures in magnetic nanostructures produced by changing the Fe–Co–Cr ratios in amorphous ribbon
Summary
Follow this and additional works at: http://repository.cmu.edu/mse Part of the Materials Science and Engineering Commons. Journal of Applied Physics, 107, 9, 09A313. E. McHenry1,2 1Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15217, USA 2Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15217, USAPresented 22 January 2010; received 3 November 2009; accepted 13 January 2010; published online 19 April 2010͒
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