Magnetic contribution to heat capacity and entropy of nickel ferrite (NiFe2O4)

Thermodynamics of Cr2O3, FeCr2O4, ZnCr2O4, and CoCr2O4

“…It is noteworthy that a second anomaly appears in the heat capacity curves for the family of chromites in the vicinity of 70-90 K that is similar to one found previously for the family of ferrites; see Table 11. In the latter cases, we found that the anomaly resembled a Schottky anomaly and was included in the contribution to C P lattice rather than C P mag [64].…”

“…and ( Further work, similar to that used to interpret heat capacity behavior of the transition metal ferrites [64], is required to extract thermodynamic changes associated with the loss of magnetic ordering in Cr 2 O 3 and to provide a C P fit that is valid down to absolute zero.…”

Immiscibility in the nickel ferrite–zinc ferrite spinel binary

“…12. It is noteworthy that a small Schottky "bump", attributed to a vibrational anomaly of octahedral Fe 3+ ions, is observed around 80 -85 K in both ferrites [15,20], see …”

“…Previously, we demonstrated how magnetic entropy for one of the end-member spinels could be extracted from high-temperature heat capacity measurements of nickel ferrite [15]. Briefly, the methodology relies on infrared spectroscopic measurements to define the lattice-vibrational (baseline) contribution to heat capacity and then fits the excess as the sum of a spin wave component and an empirical, Inden-type model.…”

“…[25] gives alternate set of IR peaks for ZnFe 2 O 4 : 552, 425, 336 and 166 cm -1 . c -θ i = hν i /k = 1.438 ν i Comparison of measured and fitted heat capacities of nickel ferrite [15]. Residual is plotted along bottom axis of graph.…”