ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
We present heat capacity and magnetic measurements of antiferromagnetic (AFM) CoO/Ni0.5Co0.5O superlattices grown by reactive sputtering. X-ray data verify the structure and the high quality of the superlattice. Neutron-diffraction studies of similar superlattices have shown AFM ordering through several bilayers despite the short-range nature of the spin interaction in the constituent materials. We have recently developed a unique thin film microcalorimeter capable of measuring thin films from 1.5 K to well above room temperature, permitting specific heat measurements on these superlattices for the first time. Magnetic measurements were made by coupling the superlattices to a 30 nm Ni81Fe19 overlayer and measuring the temperature dependence of the exchange anisotropy field. We examine the effect of exchange coupling at the interfaces by varying the thickness of the bilayers and their constituents. When the layers of the CoO/Ni0.5Co0.5O superlattice are thin, we observe a single broad heat capacity peak at a temperature between the Néel temperatures of bulk CoO and Ni0.5Co0.5O. This peak is at a temperature that corresponds to the superlattice magnetic blocking temperature, the temperature at which the exchange field goes to zero. For thicker layers, we observe the disappearance of the superlattice peak, and the emergence of two broad peaks close to the individual Néel temperatures of CoO and Ni0.5Co0.5O. We compare the temperature dependence of the specific heat of the superlattices to various models.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.358311
