Preferential Oxidation of Fe in Permalloy Films

Bajorek, C. H.; Nicolet, M.‐A.; Wilts, C. H.

doi:10.1063/1.1653842

Cited by 24 publications

(7 citation statements)

References 10 publications

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“…Bajorek et al 25 concluded that the oxide of Permalloy is composed primarily of ␣-Fe 2 O 3 based upon He-ion backscattering and x-ray fluorescence measurements. Antiferromagnetic ordering of an intentionally grown surface oxide has been inferred from both low-temperature hysteresis measurements and ferromagnetic resonance studies.…”

Section: Discussionmentioning

confidence: 99%

Surface oxidation of Permalloy thin films

2006

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The chemical and magnetic structures of oxides on the surface of Permalloy Ni 81 Fe 19 films were investigated as functions of annealing time with x-ray and polarized neutron reflectometry. For annealing times of less than one hour, the oxide consisted of a 1.5-nm-thick layer of NiO on an Fe oxide layer that was in contact with Permalloy. The Fe oxide thickness increases with annealing time with a parabolic rate constant of 10 −18 cm 2 s −1 ͑for an annealing temperature of 373 K͒. The growth of the oxide layer is limited by the rate at which oxygen appears below the NiO layer. No portion of the oxide region was found to be ferromagnetically ordered for films annealed less than one hour. The growth of the Fe oxide region is well correlated with the measured increase of the second-order magnetic susceptibility for similarly prepared samples.

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Section: Discussionmentioning

confidence: 99%

Surface oxidation of Permalloy thin films

2006

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“…We expect that the magnetic oxide formed in this experiment is most likely to be antiferromagnetic ␣-Fe 2 O 3 , which is known to form predominantly at the interface of the oxidized permalloy ͑NiFe͒ films. 16 It should be pointed that similarly, one expects to observe TMR in junctions with just one magnetic electrode and a magnetic dielectric layer. Another possible variation of this approach is to employ a junction with an antiferromagnetic electrode and ferromagnetic tunnel barrier.…”

Section: -mentioning

confidence: 99%

Spin-polarized electron tunneling across magnetic dielectric

Shvets

Григоренко

Новоселов

et al. 2005

Applied Physics Letters

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This letter deals with a magnetic tunnel junction having spin filtering by a magnetic barrier. We performed experiments in which a relatively strong external field rotates magnetizations of both ferromagnetic electrodes in the tunnel junction with the magnetic barrier simultaneously so that the two are always parallel to each other. The tunnel magnetoresistance induced in this way was over 16% at 300 K. The angular dependency of the tunnel current on the layer magnetizations indicates that the barrier contains antiferromagnetic oxide. To achieve the described effect the magnetic electrode of the junction was oxidized prior to forming the Al 2 O 3 layer. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1925785͔Conventional spin-polarized electron tunneling is based on a tunnel junction with two ferromagnetic electrodes. [1][2][3][4][5] The tunnel current between the electrodes depends on their relative orientations of magnetization with respect to each other. 6 Spin-dependent currents can also be achieved in the case of tunneling between an antiferromagnetic electrode and a ferromagnetic one. In this case, the tunnel current changes when the magnetization vector in the ferromagnetic electrode rotates with respect to the antiferromagnetic direction of the other electrode. [7][8][9] Another approach to achieving spin-dependent tunneling was proposed in Ref. 10. To explain the concept, let us consider two ferromagnetic electrodes separated by a tunnel barrier. We assume that magnetizations M 1 and M 2 in both electrodes are always parallel. Contrary to the conventional approach, however, we consider the tunnel barrier composed of a ferromagnetic dielectric. The direction of magnetization M b in the barrier is different from the direction of magnetizations M 1 and M 2 in the electrodes. In this case, the tunnel current between the two ferromagnetic electrodes, depends on the relative direction of the spin of electrons emitted by the electrodes, with respect to the magnetization of the tunnel barrier, because the tunneling electrons see interaction with the spins of the dielectric layer through an additional exchange energy −J 1 b , where J is the exchange constant and ប 1 / 2 and ប b / 2 are electron spins in the first electrode and barrier, respectively. This either increases or decreases the effective tunnel barrier depending on the relative direction of spins in the electrodes and the ferromagnetic layer. Therefore, the tunnel current at low bias voltage V iswhere signs Ϫ and ϩ in Eq. ͑1͒ correspond to the cases of the spin directions in the tunnel barrier and in the electrodes being parallel and antiparallel to each other, respectively, provided J is positive ͑ferromagnetic exchange͒ and vice versa for negative J. G is the barrier conductivity per unit area, m is the free electron mass, is the barrier height, d is the barrier width. In writing Eq. ͑1͒, we assume 100% spin polarization at the Fermi level. If J Ӷ , then the relative change of the conductivity iswhere k eff = J ͱ 2m / ͑ប ͱ ͒ and ͗G͘ is the aver...

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“…We have chosen to study the oxidation of Permalloy (Ni0.s0Fe0.2o) films using these techniques, with the intent to establish a foundation for future studies of various thin film systems. The complicated surface composition and chemistry of air-exposed Permalloy films have been studied by Pollak and Bajorek using AES and XPS (15) and the oxidation (in the 350 ~ 500~ range) of Permalloy films was carried out by Coren and Francombe (16) and by Bajorek et al (17). However, to our knowledge no kinetic data have been reported for Permalloy film oxidation.…”

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confidence: 99%