Electromagnetic (EM) characteristics of superparamagnetic graphite-coated FeNi3 nanocapsules were studied at 2–18 GHz. Compared with FeNi3 nanoparticles coated by an amorphous oxide layer, the natural resonance and attenuation properties of the graphite-coated FeNi3 nanocapsules were dramatically enhanced, due to the coating of the graphite. Graphite layers can restrain the growth of FeNi3 nanocapsules, increase the resistivity, enhance the resonance frequency, keep the real part of permeability almost constant at high frequency and increase the magnetic loss. As a result of enhanced natural resonance and attenuation properties, the FeNi3/C nanocapsules exhibit good EM absorption properties.

A large reversible negative magnetic-entropy change ⌬S M has been observed in TbCoC 2 , accompanied by a second-order phase transition at 28 K. The maximum value of −⌬S M is 15.3 J kg −1 K −1 at 30 K for a magnetic-field change from 0 to 5 T, with the refrigerant capacity of 354 J kg −1. In particular, also the large −⌬S M max of 7.8 J kg −1 K −1 , is obtained for a small field change from 0 to 2 T. The large reversible ⌬S M and the high reversible refrigerant capacity in low magnetic field indicate that TbCoC 2 may be a promising candidate for magnetic refrigeration at low temperatures.

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