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2 Apr 2012

Volume 100, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 100, 144101 (2012); http://dx.doi.org/10.1063/1.3697983 (4 pages)

H. Xu (徐涵), Wei Yu (余玮), M. Y. Yu (郁明阳), A. Y. Wong (黄燿煇), Z. M. Sheng (盛政明), M. Murakami (村上匡且), and J. Zhang (张杰)
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Magneto-optical magnetometry of individual 30 nm cobalt nanowires grown by electron beam induced deposition

E. Nikulina, O. Idigoras, P. Vavassori, A. Chuvilin, and A. Berger

Appl. Phys. Lett. 100, 142401 (2012); http://dx.doi.org/10.1063/1.3701153 (4 pages) | Cited 4 times

Online Publication Date: 2 April 2012

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We show that magnetometry measurements based upon the magneto-optical Kerr effect and high resolution optical microscopy can be used as a noninvasive probe of magnetization reversal for individual nano-structures. Our measurements demonstrate single pass hysteresis loop measurements for sample sizes down to 30 nm width. A quantitative signal-to-noise ratio evaluation shows that our approach achieves an at least 3-fold improvement in sensitivity if compared to focused laser based nano-magnetometry. An analysis of the physical limits of our detection scheme enables us to estimate that measurements for structures with single digit nm widths and magnetic moments of 10−16 Am2 are feasible.
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78.20.Ls Magneto-optical effects
81.07.Gf Nanowires
81.15.Jj Ion and electron beam-assisted deposition; ion plating
75.75.Cd Fabrication of magnetic nanostructures
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Low frequency noise in La0.7Sr0.3MnO3 based magnetic tunnel junctions

R. Guerrero, A. Solignac, C. Fermon, M. Pannetier-Lecoeur, Ph. Lecoeur, and R. Fernández-Pacheco

Appl. Phys. Lett. 100, 142402 (2012); http://dx.doi.org/10.1063/1.3698393 (4 pages) | Cited 2 times

Online Publication Date: 2 April 2012

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Magnetic tunnel junctions based on manganites can exhibit a high tunneling magnetoresistance ratio due to the almost full spin polarization at the Fermi level. However, the performances of magnetic tunnel junction devices are also strongly linked to their noise characteristics. Here, we present a low frequency noise study on fully epitaxial La0.7Sr0.3MnO3/SrTiO3/La0.7Sr0.3MnO3/La0.66Sr0.33Mn0.995Ru0.005O3 tunnel spin valves with tunneling magnetoresistance ratios larger than 100%. We evidence non-conventional low frequency noise dependence on temperature related to the magnetic fluctuations and structural phase transitions in the structure. We present also a comparison with the low frequency noise exhibited in Fe/MgO/Fe magnetic tunnel junctions.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Enhancement of carrier-mediated ferromagnetism in Zr/Fe-codoped In2O3 films

H. Kim, M. Osofsky, R. C. Y. Auyeung, and A. Piqué

Appl. Phys. Lett. 100, 142403 (2012); http://dx.doi.org/10.1063/1.3700864 (4 pages) | Cited 2 times

Online Publication Date: 3 April 2012

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Fe/Zr-codoped In2O3 thin films were grown on yttria stabilized zirconia substrates by pulsed laser deposition. The deposited films exhibited ferromagnetism at room temperature with strong magnetic anisotropy, which was influenced by a magnetostriction effect under tensile stress (i.e., c/a > 1). Both the saturation magnetization and anomalous Hall effect (AHE) were enhanced by increasing charge carrier density via Zr-doping. Our observations, including AHE and magnetic anisotropy, provide strong evidence of intrinsic ferromagnetism at room temperature in these materials.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.30.Gw Magnetic anisotropy
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Le Other inorganic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Pressure-induced ferromagnetism in open structure alkali metals from first principles

Shengjie Dong and Hui Zhao

Appl. Phys. Lett. 100, 142404 (2012); http://dx.doi.org/10.1063/1.3701134 (5 pages)

Online Publication Date: 3 April 2012

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Magnetic properties of heavier alkali metals K, Rb, and Cs in simple cubic and simple hexagonal structures at ambient and elevated simulated uniform hydrostatic pressure have been investigated using first-principles density-functional theory. The calculations exhibit the occurrence of both ferromagnetism enhancement and collapse as pressure increases and illuminate that the spin polarized interstitial electron blobs are formed by both s and p electrons. The distortion and nesting of the Fermi surface is also presented with increasing pressure.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.25.Ba Spin polarized transport in metals
61.66.Bi Elemental solids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
75.50.Cc Other ferromagnetic metals and alloys

Ab initio magnetocrystalline anisotropy at nanoscale: The case of FePt

Roman V. Chepulskii and W. H. Butler

Appl. Phys. Lett. 100, 142405 (2012); http://dx.doi.org/10.1063/1.3700746 (4 pages) | Cited 2 times

Online Publication Date: 4 April 2012

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The effect of the transition from bulk to nanoscale on the magnetocrystalline anisotropy (MCA) is studied from first principles for L10-ordered FePt nanoslabs and nanocrystals. It is shown that the nano size of slabs does not kill bulk MCA but may even slightly increase it. The effect of lattice parameter change on MCA is much stronger than that of slab thickness. The design of the shape of a nanocrystal may also be used to increase the MCA.
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75.30.Gw Magnetic anisotropy
61.46.-w Structure of nanoscale materials
75.75.-c Magnetic properties of nanostructures

Microstructure and magnetization reversal of L10-FePt/[Co/Pt]N exchange coupled composite films

H. H. Guo, J. L. Liao, B. Ma, Z. Z. Zhang, Q. Y. Jin, H. Wang, and J. P. Wang

Appl. Phys. Lett. 100, 142406 (2012); http://dx.doi.org/10.1063/1.3700865 (3 pages)

Online Publication Date: 4 April 2012

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Two series of perpendicular exchange coupled composites (ECC) films are prepared by dc magnetron sputtering, FePt(5)/[Co(0.2)/Pt(0.3)]N (ECC-I-N) and FePt(5)/[Co(0.2)/Pt(0.6)]N (ECC-II-N), respectively. Structure analyses reveal the epitaxial growth on (001) oriented L10 FePt island-like grains of [Co/Pt]N with (200) orientation. Coercivity HC and remanent coercivity HCR of both series samples decrease sharply compared to FePt, with the increase of the thickness of [Co/Pt]N. The angular dependence of HCR shows excellent angular tolerance.
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75.60.Jk Magnetization reversal mechanisms
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions

Tunable linear magnetoresistance in MgO magnetic tunnel junction sensors using two pinned CoFeB electrodes

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

Appl. Phys. Lett. 100, 142407 (2012); http://dx.doi.org/10.1063/1.3701277 (4 pages) | Cited 6 times

Online Publication Date: 4 April 2012

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MgO-barrier magnetic tunnel junction sensors with both CoFeB layers pinned by IrMn have been fabricated, which show a tunneling magnetoresistance (TMR) of up to 255% at room temperature. The perpendicular configuration for magnetic field sensing is set using a two-step field annealing process. The linear TMR field range and sensitivity are tuned by inserting an ultrathin Ru layer between the upper IrMn and the top-pinned CoFeB layer. The field sensitivity reaches 26%/mT, while the noise detectivity is about 90 nT/math at 10 Hz for a 0.3 nm Ru insertion layer. The bias dependence of the noise suggests that this is a useful design for sensor applications.
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07.55.-w Magnetic instruments and components

Theoretical investigation of organic magnetoresistance based on hyperfine interaction

X. X. Li, X. F. Dong, J. Lei, S. J. Xie, and A. Saxena

Appl. Phys. Lett. 100, 142408 (2012); http://dx.doi.org/10.1063/1.3701167 (4 pages) | Cited 1 time

Online Publication Date: 5 April 2012

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We present a theoretical calculation of magnetoresistance (MR) by including the hyperfine interaction to explain the recently discovered magnetoresistance effect in non-magnetic organic semiconductor devices. A good agreement between the theoretical results and the experimental data has been obtained. It is found that the hyperfine interaction is of fundamental importance for the occurrence of magnetoresistance effect. In addition, we also discuss the effect of electron-phonon coupling on magnetoresistance.
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72.20.My Galvanomagnetic and other magnetotransport effects
63.20.kd Phonon-electron interactions

Precession frequency and fast switching dependence on the in-plane and out-of-plane dual spin-torque polarizers

Hong Zhang, Zhiwei Hou, Jianwei Zhang, Zongzhi Zhang, and Yaowen Liu

Appl. Phys. Lett. 100, 142409 (2012); http://dx.doi.org/10.1063/1.3700724 (4 pages) | Cited 2 times

Online Publication Date: 6 April 2012

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Steady magnetization precession can be excited by a DC spin-polarized current in a spin-valve with combined in-plane (IP) and out-of-plane (OP) dual polarizers. The precession frequency is proportional to the strength of spin-torque generated by the OP polarizer but less sensitive to the IP polarizer, which can be successfully interpreted by an analytic model. A single current pulse with its duration as short as 150 ps is able to drive the magnetization switching. The switching probability is dominated by the value of the free layer angle φc at which the free layer magnetization rotation transforms to a damped small angle precession after stopping the current pulse.
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72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.Jp Ultrafast magnetization dynamics and switching

Enhancement of perpendicular magnetic anisotropy through reduction of Co-Pt interdiffusion in (Co/Pt) multilayers

S. Bandiera, R. C. Sousa, B. Rodmacq, and B. Dieny

Appl. Phys. Lett. 100, 142410 (2012); http://dx.doi.org/10.1063/1.3701585 (4 pages) | Cited 3 times

Online Publication Date: 6 April 2012

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We demonstrate that the effective magnetic anisotropy of sputtered (Co/Pt) multilayers can be doubled by limiting the interdiffusion occurring at Co/Pt interfaces. We present a way to decrease the interdiffusion by inserting an ultra-thin Cu layer at or near the Co/Pt interfaces. When such a material is sputtered on Co prior to the Pt deposition, the perpendicular magnetic anisotropy, as well as the thermal stability, is enhanced for Co layer thicknesses smaller than 1 nm. This is of great interest for out-of-plane magnetized spintronic devices which require high perpendicular magnetic anisotropy for down-size scalability reasons together with a free layer as thin as possible to reduce the writing energy when switched by spin transfer torque.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
66.30.Ny Chemical interdiffusion; diffusion barriers
75.30.Gw Magnetic anisotropy
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