Thickness dependence of magnetic and transport properties of chromium dioxide (CrO₂) strained epitaxial thin films

Chromium dioxide (CrO2) thin films of different thicknesses (120-2600 Å) have been grown epitaxially on (100)-oriented TiO2 substrates by the chemical vapor deposition technique. The thicker films, with a Curie temperature of 395 K, exhibit in-plane magnetocrystalline anisotropy with the magnetic easy axis along the c-axis direction. At low temperatures, the easy axis is deflected from the c- toward the b-axis in the thickness range 1500-600 Å. For even smaller thicknesses, the c-axis and the magnetic easy axis coincide again. However, at 300 K, the c-axis is always the magnetic easy axis in every film studied. Resistivity measurement in the temperature range of 4.2 to 420 K has also been performed. Temperature dependence of the resistivity is highly anisotropic between the b- and the c-axis, due to thickness induced anisotropic strain in the CrO2 films.