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24 Dec 2012

Volume 101, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 101, 263501 (2012); http://dx.doi.org/10.1063/1.4772532 (4 pages)

Youngki Yoon and Sayeef Salahuddin
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Thermally assisted spin-transfer torque magnetization reversal in uniaxial nanomagnets

D. Pinna, Aditi Mitra, D. L. Stein, and A. D. Kent

Appl. Phys. Lett. 101, 262401 (2012); http://dx.doi.org/10.1063/1.4773053 (4 pages) | Cited 1 time

Online Publication Date: 26 December 2012

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We simulate the stochastic Landau-Lifshitz-Gilbert dynamics of a uniaxial nanomagnet out to sub-millisecond timescales using a graphical processing unit based micromagnetic code and determine the effect of geometrical tilts between the spin-current and uniaxial anisotropy axes on the thermally assisted reversal dynamics. The asymptotic behavior of the switching time (I→0, 〈τ〉∝exp(−ξ(1−I)2)) is approached gradually, indicating a broad crossover regime between the ballistic and thermally assisted spin transfer reversal. Interestingly, the functional form of the mean switching time is shown to be independent of the angle between the spin current and magnet's uniaxial axes. These results have important implications for modeling the energetics of thermally assisted magnetization reversal of spin transfer magnetic random access memory bit cells.
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75.60.Jk Magnetization reversal mechanisms
75.75.-c Magnetic properties of nanostructures
75.78.-n Magnetization dynamics
75.30.Gw Magnetic anisotropy
75.50.Tt Fine-particle systems; nanocrystalline materials

Yoke-shaped MgO-barrier magnetic tunnel junction sensors

J. Y. Chen, N. Carroll, J. F. Feng, and J. M. D. Coey

Appl. Phys. Lett. 101, 262402 (2012); http://dx.doi.org/10.1063/1.4773180 (4 pages)

Online Publication Date: 26 December 2012

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Yoke-shaped sensors based on MgO-barrier magnetic tunnel junctions have been designed, fabricated, and studied; they show a good linear tunneling magnetoresistance (TMR) response. A nearly-perpendicular configuration of two ferromagnetic electrodes was set by two-step annealing together with shape anisotropy. The low-frequency noise characterization shows these yoke-shaped TMR sensors have relatively low magnetic 1/f noise. The field sensitivity is up to 27%/mT, while the field detectivity reaches 4.6 nT/math at 10 Hz and 460 pT/math at 1 kHz. These TMR sensors may be useful for applications such as biomagnetic detection.
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85.75.Ss Magnetic field sensors using spin polarized transport
07.55.-w Magnetic instruments and components
75.47.Lx Magnetic oxides
81.40.Gh Other heat and thermomechanical treatments

Magnetoresistive effect of a topological-insulator waveguide in the presence of a magnetic field

Yuan Li, Mansoor B. A. Jalil, Seng Ghee Tan, Guanghui Zhou, and Zhenghong Qian

Appl. Phys. Lett. 101, 262403 (2012); http://dx.doi.org/10.1063/1.4773489 (4 pages)

Online Publication Date: 26 December 2012

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We investigate the transport properties of a topological insulator (TI) waveguide in the presence of an external magnetic field. We demonstrate that the magnetic field can modulate the energy gap induced by the transverse confinement and may even result in the closure of the band gap. The dependence of the magnetic field and the temperature on the magnetoresistance (MR) is also analyzed. The MR ratio increases linearly and exhibits a nonsaturation behaviour at high fields. The MR behavior also exhibits weak temperature dependence such that a high MR is maintained over a broad temperature range. The robustness of the MR up to room temperature can be exploited for magneto-electronic device applications.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.20.At Surface states, band structure, electron density of states

Stochastic switching asymmetry in magnetoresistive stacks due to adjacent nanowire stray field

M. T. Bryan, N. A. Porter, J. S. Claydon, M. A. Bashir, G. Burnell, C. H. Marrows, T. Schrefl, and D. A. Allwood

Appl. Phys. Lett. 101, 262404 (2012); http://dx.doi.org/10.1063/1.4773370 (4 pages)

Online Publication Date: 27 December 2012

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Giant-magnetoresistance was used to measure the switching of patterned multilayer stacks either close to or removed from a ferromagnetic nanowire. Stray fields from the nanowire greatly changed the stack's free layer hysteresis characteristics. Four distinct switching modes were observed when the applied field opposed the pinned layer magnetization, but reproducible switching occurred otherwise. Micromagnetic modeling suggested that the asymmetry was due to interlayer stray field interactions and the Oersted field from the measuring current, while the switching modes were due to transverse components from the nanowire stray field. The results demonstrate the feasibility of remote electrical detection of nanowire magnetization.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Alternating domains with uniaxial and biaxial magnetic anisotropy in epitaxial Fe films on BaTiO3

Tuomas H. E. Lahtinen, Yasuhiro Shirahata, Lide Yao, Kévin J. A. Franke, Gorige Venkataiah, Tomoyasu Taniyama, and Sebastiaan van Dijken

Appl. Phys. Lett. 101, 262405 (2012); http://dx.doi.org/10.1063/1.4773482 (4 pages) | Cited 2 times

Online Publication Date: 27 December 2012

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We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a–c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a–c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
62.20.D- Elasticity
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms

Spin precession modulation in a magnetic bilayer

A. Stupakiewicz, M. Pashkevich, A. Maziewski, A. Stognij, and N. Novitskii

Appl. Phys. Lett. 101, 262406 (2012); http://dx.doi.org/10.1063/1.4773508 (4 pages)

Online Publication Date: 27 December 2012

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We report on modulation of the spin precession in a Co/garnet bilayer by femtosecond laser excitation using time-resolved magneto-optical tools. Damped oscillations in the Faraday rotation transients representing precessional motion of the magnetization vector are observed in both the 2 nm Co layer and 1.8 μm garnet of the bilayer with distinct frequencies differing by about a factor of two. The excitation efficiency of these precessions strongly depends on the out-of-plane magnetic field. The modulation effect with the coupling in a magnetic bilayer can be useful for non-thermally controlling the magnetization of nanomagnets and ultrafast switching in magnetic nanodevices.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Investigation of induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers

Stephan Geprägs, Sibylle Meyer, Stephan Altmannshofer, Matthias Opel, Fabrice Wilhelm, Andrei Rogalev, Rudolf Gross, and Sebastian T. B. Goennenwein

Appl. Phys. Lett. 101, 262407 (2012); http://dx.doi.org/10.1063/1.4773509 (4 pages) | Cited 2 times

Online Publication Date: 28 December 2012

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Using X-ray magnetic circular dichroism (XMCD) measurements, we explore the possible existence of induced magnetic moments in thin Pt films deposited onto the ferrimagnetic insulator yttrium iron garnet (Y3Fe5O12). Such a magnetic proximity effect is well established for Pt/ferromagnetic metal heterostructures. Indeed, we observe a clear XMCD signal at the Pt L3 edge in Pt/Fe bilayers, while no such signal can be discerned in XMCD traces of Pt/Y3Fe5O12 bilayers. Integrating the XMCD signals allows to estimate an upper limit for the induced Pt magnetic polarization in Pt/Y3Fe5O12 bilayers.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
81.15.Dj E-beam and hot filament evaporation deposition
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
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