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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Magnetoresistance and magnetization reversal process of Co nanowires covered with Pt

B. Hausmanns, T. P. Krome, and G. Dumpich

J. Appl. Phys. 93, 8095 (2003); http://dx.doi.org/10.1063/1.1540054 (3 pages) | Cited 26 times

Online Publication Date: 9 May 2003

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The magnetoresistance (MR) of single Co nanowires of various width is investigated at low temperatures in magnetic fields up to 5 T. The in-plane longitudinal MR shows pronounced features at coercive fields indicating the magnetization reversal process. The nanowires are prepared by electron beam lithography. Some of the wires are covered with a 2 nm thick Pt layer, the others are uncovered. The MR behavior of the Pt covered Co nanowires shows significantly different behavior from that of the uncovered nanowires. This is interpreted mainly as arising from an oxidation of the Co surface leading to a formation of an antiferromagnetic CoO layer on top of the uncovered Co nanowires. The CoO layer hinders the magnetization reversal process by domain wall pinning, which is reflected by the MR behavior of these samples. In contrast, the MR behavior of the Pt covered Co nanowires shows no pinning effects. Thus, we conclude that covering the Co nanowires in situ with a 2 nm thick Pt layer prevents oxidation effects. © 2003 American Institute of Physics.
Show PACS
75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.47.Np Metals and alloys
81.65.Mq Oxidation
73.63.Nm Quantum wires
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure

Simultaneous detection of perpendicular and in-plane magnetization component in a [Co/Pd]n perpendicular magnetic recording media

Sarbanoo Das, Hironori Yoshikawa, and Shigeki Nakagawa

J. Appl. Phys. 93, 8098 (2003); http://dx.doi.org/10.1063/1.1540055 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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Hall effect measurement has been used to detect the perpendicular and in-plane magnetization components simultaneously in a [Co/Pd]n multilayer thin film with strong magnetic anisotropy along the direction perpendicular to the film plane. The angle between the driving current direction and the in-plane projection of the applied magnetic field was varied to investigate the contribution of in-plane magnetization component to the measured Hall voltage. Hall voltage under the canted magnetic field revealed that the output is the superposition of the anomalous Hall effect (AHE) due to the perpendicular component of magnetization and the planar Hall effect (PHE) due to the in-plane magnetization component. Odd symmetry characteristics of AHE and even symmetry characteristics of PHE with respect to applied field have been applied to extract the Hall voltage contributed by the two different magnetization components from their combined characteristic. Anomalous Hall voltage from the perpendicular magnetization component exhibited an irreversible hysteresis loop while that from the in-plane magnetization component was found almost reversible with respect to applied magnetic field. The method was effective to evaluate the in-plane component of magnetization in an ultrathin film under the canted magnetic field. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys

Transport anisotropy in hetero-amorphous (CoFeB)–SiO2 thin films

P. Johnsson, S.-I. Aoqui, A. M. Grishin, and M. Munakata

J. Appl. Phys. 93, 8101 (2003); http://dx.doi.org/10.1063/1.1558238 (3 pages) | Cited 6 times

Online Publication Date: 9 May 2003

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We here present resisitivity and magnetoresistance measurements of two granular (CoFeB)–SiO2 amorphous thin films, with a different amount of metallic content. The films were deposited onto substrates sitting on a rotating cylinder. This induces anisotropy in the film plane, which is higher for the sample with less metallic content. This film exhibits typical isotropic giant magnetoresistance (GMR), while the film with higher-metallic content has less anisotropic resistivity, and shows a mixture of GMR and anisotropic magnetoresistance (AMR). The AMR appears at fields below 500 Oe. We believe that this has not been observed before in amorphous samples. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Ak Magnetic properties of monolayers and thin films
73.61.-r Electrical properties of specific thin films
75.50.Kj Amorphous and quasicrystalline magnetic materials

Magnetoresistance magnetometry of (Ni80Fe20)1−xIrx wires with varying anisotropic magnetoresistance ratio

C. A. F. Vaz, E. Blackburn, M. Kläui, J. A. C. Bland, Li Gan, W. F. Egelhoff, E. Cambril, G. Faini, and W. Wernsdorfer

J. Appl. Phys. 93, 8104 (2003); http://dx.doi.org/10.1063/1.1540056 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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We report room and low temperature magnetoresistance measurements on submicrometer scale elements (wires and crosses, 1.0, 0.5, and 0.1 μm) of (Ni80Fe20)1−xIrx (x≈2%) with varying Ir concentrations. For the particular Ir concentrations studied, the anisotropic magnetoresistance (AMR) ratio varied between −0.043% and −0.035% at room temperature. For the single wires (0.5–1 μm) the MR versus field characteristic is similar to that reported for Ni80Fe20 wires of similar size, but an opposite sign of the AMR is observed for x>2%. For H parallel to the wire axis, the reversal is determined by the sweeping of a few domains which give rise to “ears” in the MR–H characteristic. For H perpendicular to the wire, a parabolic variation is seen corresponding to rotation of the magnetization, but a negative slope in the MR-H characteristic is obtained at high fields as in permalloy wires. This suggests that the high field behavior originates from a distinctly different mechanism (e.g., surface scattering) from that of AMR. © 2003 American Institute of Physics.
Show PACS
75.75.-c Magnetic properties of nanostructures
75.60.Jk Magnetization reversal mechanisms
75.47.Np Metals and alloys
73.63.Nm Quantum wires
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
73.25.+i Surface conductivity and carrier phenomena

Anomalous Hall resistivity due to grain boundary in manganite thin films

T. Taniyama, K. Hamaya, Y. Kitamoto, and Y. Yamazaki

J. Appl. Phys. 93, 8107 (2003); http://dx.doi.org/10.1063/1.1543865 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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Anomalous Hall resistivities of polycrystalline manganite thin films with different grain sizes are reported. Positive anomalous Hall coefficients due to grain boundaries are clearly observed besides a negative contribution in the bulk manganite. The positive contribution becomes pronounced with decreasing grain size in the polycrystalline samples, reaching up to 4.2 μΩ cm at 5 K. The temperature dependence of the anomalous Hall resistivity is in good agreement with its magnetoresistive feature. Possible causes for the anomalous contribution are discussed within existing models for granular magnetoresistive thin films or multilayers. © 2003 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
61.72.Mm Grain and twin boundaries
68.55.-a Thin film structure and morphology
73.61.Ng Insulators
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Domain model for the magnetoimpedance of metallic ferromagnetic wires

I. Betancourt, R. Valenzuela, and M. Vazquez

J. Appl. Phys. 93, 8110 (2003); http://dx.doi.org/10.1063/1.1558239 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2003

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Complex inductance formalism (L) is used to calculate the complex circular permeability (μcirc) in a domain model for the magnetoimpedance (MI) of soft ferromagnetic wires. An excellent agreement between calculated and experimental values of μcirc as a function of frequency is observed. In addition, a very good agreement is also exhibited between experimental and calculated plots of μcirc as a function of an applied dc magnetic field before and above the relaxation frequency (also known as single- and double-peak MI effect). These results confirm the validity of L as an alternative approach to MI phenomena in soft ferromagnetic wires. © 2003 American Institute of Physics.
Show PACS
75.47.Np Metals and alloys
75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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