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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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back to top Magnetic Tunnel Junctions I

Magnetic tunnel junctions with Hf oxide and modified Hf oxide tunnel barriers

B. G. Park, T. D. Lee, T. H. Lee, C. G. Kim, and C. O. Kim

J. Appl. Phys. 93, 6423 (2003); http://dx.doi.org/10.1063/1.1540141 (3 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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Magnetic tunnel junctions (MTJ’s) with Hf oxide and modified Hf oxide barriers were fabricated by ozone oxidation. The tunnel magnetoresistance (TMR) ratio in Hf oxide junction was 13% at room temperature and 21% at 77 K. In order to understand the low TMR ratio in MTJ’s with Hf oxides compared to those with Al oxides, tunnel barriers were modified by inserting a thin Al oxide layer of 0.3 nm at the interfaces between ferromagnetic electrodes and Hf oxide insulating layers. As the Al layer of 0.3 nm was inserted at top and bottom interfaces, the TMR ratio was restored to the value of the junctions with Al oxides. This implies that the polarization of CoFe contacted with Al oxide is larger than that of CoFe contacted with Hf oxide and the low TMR ratio in MTJ’s with Hf oxides may be attributed to the reduction of spin polarization of the CoFe electrodes due to CoFe/Hf oxide interface interaction. © 2003 American Institute of Physics.
Show PACS
85.75.Dd Magnetic memory using magnetic tunnel junctions
75.47.Pq Other materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.65.Mq Oxidation

Magnetic tunnel-valve barriers with boron

J. R. Childress, J.-S. Py, M. K. Ho, R. E. Fontana, and B. A. Gurney

J. Appl. Phys. 93, 6426 (2003); http://dx.doi.org/10.1063/1.1556925 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The properties of magnetic tunnel junctions with aluminum oxide barriers alloyed with boron are presented. When aluminum is deposited by sputtering, 10 at. % B addition is sufficient to completely transform the deposited Al film from crystalline to amorphous. We have investigated if the deposition of amorphous AlB prior to oxidation results in a variation of tunnel-valve properties. It is found that ultrathin Al90B10 films can be readily oxidized using a procedure similar to that for Al films, resulting in tunnel valves with good magnetic properties. In the ultrathin regime (when the specific junction resistance is Rj<20 Ω μm2), the barriers with boron yield magnetoresistance values slightly above that of pure aluminum oxide, although the effect is not significant for Rj<5 Ω μm2. © 2003 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness

Atomic, electronic, and magnetic properties of magnetic tunnel junctions

I. I. Oleynik and E. Yu. Tsymbal

J. Appl. Phys. 93, 6429 (2003); http://dx.doi.org/10.1063/1.1558631 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2003

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We report results of first-principles density-functional studies of the atomic and electronic structure of Co/Al2O3/Co and Co/SrTiO3/Co magnetic tunnel junctions (MTJs). The atomic structure has been studied for different interface terminations and the interfacial energetics was quantified based on the work of separation. Based on energetics of cohesion, the O-terminated and TiO2-terminated interfaces were identified as the most stable structures for Co/Al2O3/Co and Co/SrTiO3/Co MTJs, respectively. The electronic structure was analyzed using local densities of states. We found that the electronic structure of the O-terminated Co/Al2O3/Co tunnel junction exhibits negative spin polarization at the Fermi energy within the first few monolayers of alumina but it eventually becomes positive for distances beyond 10 Å. Calculated electronic structure of the TiO2-terminated Co/SrTiO3/Co MTJ shows an exchange coupling between the interface Co and Ti atoms mediated by oxygen. This coupling induces a magnetic moment of 0.25 μB on the interface Ti atom, which is aligned antiparallel to the magnetic moment of the Co layer. This is a possible cause of inversion of the spin polarization of tunneling across the SrTiO3 barrier that was found in recent experiments. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Ct Interface structure and roughness
73.20.-r Electron states at surfaces and interfaces
72.25.Mk Spin transport through interfaces
75.47.-m Magnetotransport phenomena; materials for magnetotransport
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.30.Et Exchange and superexchange interactions
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