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18 Oct 2010

Volume 97, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 97, 162901 (2010); http://dx.doi.org/10.1063/1.3501139 (3 pages)

Wei-Feng Rao, Ke-Wei Xiao, Tian-Le Cheng, Jie E. Zhou, and Yu U. Wang
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Reverse Schottky-asymmetry spin current detectors

Yuan Lu and Ian Appelbaum

Appl. Phys. Lett. 97, 162501 (2010); http://dx.doi.org/10.1063/1.3504659 (3 pages)

Online Publication Date: 18 October 2010

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By reversing the Schottky barrier-height asymmetry in hot-electron semiconductor-metal-semiconductor ballistic spin filtering spin detectors, we have achieved the following: (1) demonstration of >50% spin polarization in silicon, resulting from the increase of detection efficiency by elimination of the ferromagnet/silicon interface on the transport channel detector contact and (2) evidence of spin transport at temperatures as high as 260 K, enabled by an increase in detector Schottky barrier height.
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85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
72.25.Mk Spin transport through interfaces
73.30.+y Surface double layers, Schottky barriers, and work functions
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Magnetic force microscopy of epitaxial magnetite films through the Verwey transition

A. K. H. Lee, P. B. Jayathilaka, C. A. Bauer, M. C. Monti, J. T. Markert, A. de Lozanne, and Casey W. Miller

Appl. Phys. Lett. 97, 162502 (2010); http://dx.doi.org/10.1063/1.3502606 (3 pages)

Online Publication Date: 18 October 2010

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Magnetic force microscopy was performed on 300 nm thick magnetite films grown epitaxially on MgO (001) at temperatures ranging from well below to well above the Verwey transition temperature, TV. Frequency shift images were acquired at different locations on the sample as temperature was increased through the Verwey transition. The magnetic domain features are persistent at all temperatures, which indicates that the domains are pinned across the phase transition, probably due to antiphase boundaries. An enhancement of magnetic contrast below TV indicates the moments tilt out of the plane below TV, which is corroborated by superconducting quantum interference device magnetometry.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.-a Thin film structure and morphology
75.30.Cr Saturation moments and magnetic susceptibilities

Phase periodic conductance oscillations at subgap Andreev resonances in Nb–Al–AlOx–Al–Nb tunnel junctions

Kartik Senapati, Mark G. Blamire, and Zoe H. Barber

Appl. Phys. Lett. 97, 162503 (2010); http://dx.doi.org/10.1063/1.3504258 (3 pages)

Online Publication Date: 18 October 2010

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We show evidence of a magnetic field dependent oscillation of subgap dynamic conductivity in a series of Nb–Al–AlOx–Al–Nb Josephson tunnel junctions in the voltage biased state. Our measurements show that the amplitude of conductance oscillations was maximum close to the subharmonic conductance peaks of the junctions, which are collective resonances of multiple Andreev reflected quasiparticles via pinholes in the tunnel barrier. The period of oscillations was commensurate with the macroscopic phase evolution of the junction. This observation suggests that under certain conditions practical Josephson tunnel junctions are analogous to Andreev interferometers, where the junction itself acts as the flux quantizer.
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85.25.Cp Josephson devices
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions

High room temperature ferromagnetic moment of Ho substituted nanocrystalline BiFeO3

Pankaj Thakuria and P. A. Joy

Appl. Phys. Lett. 97, 162504 (2010); http://dx.doi.org/10.1063/1.3502481 (3 pages) | Cited 1 time

Online Publication Date: 19 October 2010

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Magnetic properties of trivalent rare-earth ion substituted nanocrystalline BiFeO3 have been studied for the compositions Bi0.875R0.125FeO3 (R = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb). All compositions show ferromagnetic characteristics at room temperature, with enhanced magnetization after substitution. Very high magnetization (at 6 T), almost three times that of the unsubstituted composition, is observed for R = Ho, and highest remnant magnetization is obtained for R = Nd and Sm. The magnetic transition temperature is increased by ∼ 20 K for R = La. The results show that it is possible to tune the magnetic characteristics of the nanocrystalline multiferroic BiFeO3 by the choice of the rare-earth ion.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
75.50.Dd Nonmetallic ferromagnetic materials
75.85.+t Magnetoelectric effects, multiferroics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Analytical solutions of the Ginzburg–Landau equations for deformable superconductors in a weak magnetic field

Huadong Yong, Fangzhong Liu, and Youhe Zhou

Appl. Phys. Lett. 97, 162505 (2010); http://dx.doi.org/10.1063/1.3504661 (3 pages) | Cited 1 time

Online Publication Date: 21 October 2010

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The objective of this paper is to obtain the analytical solutions which satisfy the differential Ginzburg–Landau equations and some boundary conditions. Based on the linear deformation theory, the effects of prestrain on the wave function and magnetic potential of deformable superconductors have been investigated in the presence of a weak magnetic field. The results show that for the superconductors with a linearly elastic deformation, the wave function in the materials should be considered for two different cases, i.e., type I and type II. The prestrain effect in deformable superconductors should not be neglected in determining the superconductivity in superconductors.
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74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
74.20.De Phenomenological theories (two-fluid, Ginzburg-Landau, etc.)

Tuning the permeability of permalloy films for on-chip inductor applications

Tawab Dastagir, Wei Xu, Saurabh Sinha, Hao Wu, Yu Cao, and Hongbin Yu

Appl. Phys. Lett. 97, 162506 (2010); http://dx.doi.org/10.1063/1.3502478 (3 pages) | Cited 3 times

Online Publication Date: 21 October 2010

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In this work, we demonstrate that the permeability of 1 μm thick NiFe/Cr multilayer films can be tuned by varying the thickness of individual NiFe layers while keeping the total multilayer film thickness constant. Our results show that the permeability can be increased from 170 to 650 by varying the NiFe thicknesses from 100 to 50 nm. The thickness dependant permeability variation was attributed to the presence of stripe domains, as examined by hysteresis measurements and magnetic force microscope imaging. Films with thinner NiFe layers coupled with on-chip spiral inductors enable an inductance increase by a factor of 6.
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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)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.Fg Dynamics of domain structures

Tilting of the spin orientation induced by Rashba effect in ferromagnetic metal layer

Ung Hwan Pi, Kee Won Kim, Ji Young Bae, Sung Chul Lee, Young Jin Cho, Kwang Seok Kim, and Sunae Seo

Appl. Phys. Lett. 97, 162507 (2010); http://dx.doi.org/10.1063/1.3502596 (3 pages) | Cited 5 times

Online Publication Date: 22 October 2010

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We devised a method to measure the virtual magnetic field induced by Rashba effect in ferromagnetic metal layer. Transverse Rashba magnetic field makes the magnetization direction tilted out of the easy axis, which could be detected by the change in anomalous hall resistances. Through a specified measurement of the second harmonics of the hall resistance, the Rashba field could be obtained with high sensitivity even at low current regime. The results are compared with the prior reports based on the measurement of the transverse field required for the nucleation of reversed domain.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Cc Other ferromagnetic metals and alloys

rf auto-oscillations in antiferromagnetically coupled layers with different coupling strengths

Takeshi Seki, Hiroyuki Tomita, Teruya Shinjo, and Yoshishige Suzuki

Appl. Phys. Lett. 97, 162508 (2010); http://dx.doi.org/10.1063/1.3505357 (3 pages) | Cited 4 times

Online Publication Date: 22 October 2010

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rf auto-oscillation induced by spin-transfer torque was investigated in Fe/Cr/Fe systems that had antiferromagnetically coupled Fe layers. As the coupling strength increased, the generation linewidth (Δf) reduced remarkably whereas the oscillation frequency (f) and the onset current of the auto-oscillation increased. The strong antiferromagnetic coupling led to less variation in f depending on the bias current. These results indicate that the antiferromagnetic coupling allows us to reduce Δf and to control the nonlinearity of the rf auto-oscillation.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.47.De Giant magnetoresistance
72.25.Mk Spin transport through interfaces

Interface effects on an ultrathin Co film in multilayers based on the organic semiconductor Alq3

A. A. Sidorenko, C. Pernechele, P. Lupo, M. Ghidini, M. Solzi, R. De Renzi, I. Bergenti, P. Graziosi, V. Dediu, L. Hueso, and A. T. Hindmarch

Appl. Phys. Lett. 97, 162509 (2010); http://dx.doi.org/10.1063/1.3505495 (3 pages) | Cited 2 times

Online Publication Date: 22 October 2010

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The effect of the AlOx barrier thickness on magnetic and morphological properties of Ta/Co/(AlOx)/Alq3/Si hybrid structures was systematically studied by means of atomic force microscopy, superconducting quantum interference device magnetometry, and nuclear magnetic resonance (NMR). All used techniques pointed out that the barrier thickness of 2 nm is required to obtain a magnetically good cobalt layer on top of Alq3. 59Co NMR measurements revealed that the AlOx barrier gives rise to the formation of an interface layer with “defective” cobalt favoring growth of “bulk” cobalt with good magnetic properties.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.60.-k Nuclear magnetic resonance and relaxation
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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