Date of Original Version
Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article may be found at http://dx.doi.org/10.1063/1.3349043
Abstract or Description
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.
Journal of Applied Physics, 107, 9, 09A313.