Magnetic field dependent heat capacity of the molecule-based magnetic material NBu4[FeIIFeIII(ox)3] (Bu = n-C4H9+, ox = oxalate)

The effect of magnetic field on the heat capacity of molecule-based ferrimagnetic material NBu4[(FeFeIII)-Fe-II(ox)(3)] has been studied in 2-60 K range under different applied magnetic fields. Though the field induced changes in the heat capacities at a particular measuring temperature are small, the nature of the variation is strongly temperature dependent. The magnetic heat capacity is tentatively fitted with the relation C-mag = alpha H-beta in two magnetic field ranges: H < 5 kOe and 5 kOe less than or equal to H less than or equal to 90 kOe, The temperature variation of parameter beta exhibits two sharp minima below and above 30 K, and this observation may be the manifestation of the existence of different spin structures above and below 30 K. These results are in good correlation with the negative magnetization phenomenon, mu-SR results and observed heat capacity studies previously reported for this material. (C) 2000 Elsevier Science Ltd. All rights reserved.