Calorimetric investigation on the paramagnetic–antiferromagnetic phase transition in CoO

Colossal intrinsic exchange bias from interfacial reconstruction in epitaxial CoFe2O4/Al2O3 thin films

“…Both HEB and HC along out-of-plane and in-plane directions demonstrate similar unimodal trend in temperature, with the maximum values at approximately T = 25 K. While the HEB disappear at around T = 250 K, HC reaches their minima (about 1kOe) in the 250 -300 K range. Although the Néel temperature of bulk CoO is about 290 K [28], the value for thin films may reduce due to the finite-size effects [29]. For example, the Néel temperature of a 2-nm-thick CoO layer may reduce to 250 K [29], which is consistent with the temperature range at which the out-of-plane and in-plane HEB disappear, as shown in Fig.…”

Latent heat at the magnetic transition in CoO

“…In the close vicinity of the critical temperature, the poorest quality samples gave rounded peaks with the same shape as those that can be found in literature; it is from this kind of data that a second-order nature had been claimed and specific universality classes assigned by other authors. [21][22][23] As we obtained sharper peaks, the values of the critical parameters moved away from any universality class, invalidating previous analysis and indicating that the picture is not as simple as thought. Though there are many second-order transitions for which no universality class is found or which present abnormal critical parameters, taking into account the results of renormalization-group theory, as well as the character of FeO and MnO, the possibility that the transition in CoO has a weak first-order character must be considered; this would not have been revealed up to now due to any combination of the following reasons: the particular samples used, the resolution of the measurements performed or the experimental techniques employed.…”

Critical behavior of CoO and NiO from specific heat, thermal conductivity, and thermal diffusivity measurements

“…It is worth noting that this blunt specific heat is similar to all previously reported in literature. 11,15,17 Sample 3 exhibits a sharper feature, whereas sample 4 shows a high sharpness, which indicates the higher quality of this crystal ͑high purity, better stoichiometry, fewer defects, etc.͒. However, even for this sample, no thermal hysteresis has been found.…”

“…[5][6][7][8][9][10] On the other hand, CoO has been traditionally considered to be second order according to different types of experimental measurements. [11][12][13][14][15][16][17] However, when analyzing the critical behavior, no agreement has been obtained: some of the results are close to those predicted by the threedimensional ͑3D͒ Ising model, 11,12,17 but a 3D-Heisenberg behavior has also been reported. 15,16 Moreover, a recent crystallographic study suggests that the transition should be discontinuous since the magnetic ordering is coupled to a cubic to monoclinic symmetry breaking, in addition to the already known tetragonal distortion.…”