Observation of the Curie Transition in Palladium Bionanomaterial Using Muon Spin Rotation Spectroscopy

Palladium bionanomaterial was manufactured using the sulfate-reducing bacterium, Desulfovibrio desulfuricans, to reduce soluble Pd(II) ions to cell-bound Pd(0). The material was examined using a Superconducting Quantum Interference Device (SQUID) to observe bulk magnetisation over the temperature range 10 - 300 K and by Muon Spin Rotation (µSR), which is a probe of the local magnetic environment inside the sample, over the temperature range 200 - 700 K. Results from SQUID were used to model the temperature dependence of ferromagnetic and paramagnetic components of the bulk magnetisation and, by extrapolation, to predict the Curie transition temperature. Results from µSR confirmed the accuracy of the prediction to within 20 K. The Curie transition, which started at 528 K, was shown to be spread over a wide (> 100 K) range. This was attributed to dependence of the transition on particle size and the range of particle sizes in the population. A competing contribution to the overall magnetisation was observed due to partial thermal decomposition of the organic component of the material.