Thermodynamic measurements of magnetic ordering in antiferromagnetic superlattices

Direct measurements of heat capacity from 80 to 540 K of antiferromagnetic superlattices of NiO (high Neel temperature TN), COO (low T-N), and MgO (nonmagnetic) are used to study the effect of exchange coupling and layer thickness on magnetic ordering: NiO/CoO superlattices with thin layers show a single heat capacity peak similar to a Ni0.5Co0.5O alloy; with increasing layer thickness, the peak splits into two maxima Finite size effects are seen in uncoupled NiO and CoO. Observed shifts in TN show the importance of correlation lengths and spin fluctuations in the ordering.