HIGH-FIELD HALL EFFECT AND BAND STRUCTURE OF HALF-METALLIC CrO2 FILMS

The Hall effect of (100)- and (110)-oriented films of the half-metallic ferromagnetic oxide CrO2, fabricated by both chemical vapor deposition and high pressure, thermal decomposition methods, has been examined in large magnetic fields up to 60 T. In all cases the Hall effect exhibits a sign reversal from positive to negative with increasing field, which we take as evidence for multi-band behavior. (110) films fabricated by both methods exhibit this sign reversal at relatively low fields. The data may be fit with a simple two-band model, which indicates the existence of highly mobile holes of p-like parentage, along with a much larger number of heavy, d-like electrons. In the (100) film the sign reversal is at much higher field. The parameters obtained from the fits allow us (with help from band structure calculations) to infer the band structure near the Fermi level and how it depends on sample strain and other structural characteristics. These details will be important for understanding carrier transport through interfaces such as for spin injection or other "spintronics" applications.