Browsing by Author "Cohen, L. F."
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- Coexistence of Universal and Topological Anomalous Hall Effects in Metal CrO2 Thin Films in the Dirty LimitPublication . Branford, W. R.; Yates, Karen A.; Barkhoudarov, E.; Moore, J. D.; Morrison, K.; Magnus, F.; Miyoshi, Y.; Sousa, P. M.; Conde, O.; Silvestre, António Jorge; Cohen, L. F.The scaling exponent of 1.6 between anomalous Hall and longitudinal conductivity, characteristic of the universal Hall mechanism in dirty-metal ferromagnets, emerges from a series of CrO2 films as we systematically increase structural disorder. Magnetic disorder in CrO2 increases with temperature and this drives a separate topological Hall mechanism. We find that these terms are controlled discretely by structural and magnetic defect populations, and their coexistence leads to apparent divergence from exponent 1.6, suggesting that the universal term is more prevalent than previously realized.
- Structural and Microanalytical Studies of CrO2 Thin Films on c-Sapphire by High Resolution Electron Microscopy MethodsPublication . Ortiz, M. I.; Sousa, P. M.; Ballesteros, C.; Jorge Silvestre, António; Cohen, L. F.; Conde, O.Chromium dioxide (CrO2) has been extensively used in the magnetic recording industry. However, it is its ferromagnetic half-metallic nature that has more recently attracted much attention, primarily for the development of spintronic devices. CrO2 is the only stoichiometric binary oxide theoretically predicted to be fully spin polarized at the Fermi level. It presents a Curie temperature of ∼ 396 K, i.e. well above room temperature, and a magnetic moment of 2 mB per formula unit. However an antiferromagnetic native insulating layer of Cr2O3 is always present on the CrO2 surface which enhances the CrO2 magnetoresistance and might be used as a barrier in magnetic tunnel junctions.
- The spin polarization of CrO2 revisitedPublication . Yates, Karen A.; Branford, W. R.; Magnus, F.; Miyoshi, Y.; Morris, B.; Cohen, L. F.; Sousa, P. M.; Conde, O.; Silvestre, António JorgeHere, we use Andreev reflection spectroscopy to study the spin polarization of high quality CrO2 films. We study the spin polarization as a function of growth temperature, resulting in grain size and electrical resistivity. In these films low temperature growth appears to be a necessary but not sufficient condition to guarantee the observation of high spin polarization, and this is only observed in conjunction with suppressed superconducting gap values and anomalously low interface properties. We suggest that this combination of observations is a manifestation of the long range spin triplet proximity effect. (C) 2007 American Institute of Physics.