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5 Dec 2005

Volume 87, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 87, 234101 (2005); http://dx.doi.org/10.1063/1.2140082 (3 pages)

Ben McMillen, Chuck Jewart, Michael Buric, Kevin P. Chen, Yuankun Lin, and Wei Xu
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Action of strong coupling on steplike magnetization and transport properties in phase-separated manganite

Guixin Cao, Jincang Zhang, Yan Xu, Shipeng Wang, Jian Yu, Shixun Cao, Chao Jing, and Xuechu Shen

Appl. Phys. Lett. 87, 232501 (2005); http://dx.doi.org/10.1063/1.2135882 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2005

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For phase-separated La0.275Pr0.35Ca0.375MnO3 manganite, a steplike charge-ordered antiferromagnetic-ferromagnetic transition was observed by field induction and accompanied by a sudden drop of resistivity. The results can be explained in terms of the spin reorientation in the antiferromagnetic (AFM) phase and simultaneous destruction of orbital ordering by a magnetic field. Combined with specific heat and magnetization measurements, the electronic state density at Fermi energy was greatly enhanced at 5 T, which shows the increase of carrier number due to delocalization effect, by analogy with the spin reorientation due to destruction of orbital ordering by magnetic field. The present results prove that the strong coupling among spin, charge, and orbital ordering would be the main cause of existing complex physical behavior at low temperature, which depends sensitively on the spin orientation of adjacent charge-ordered AFM domains and can be controlled by applied field.
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75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
65.40.Ba Heat capacity
75.60.Ch Domain walls and domain structure

Spin transfer switching and spin polarization in magnetic tunnel junctions with MgO and AlOx barriers

Zhitao Diao, Dmytro Apalkov, Mahendra Pakala, Yunfei Ding, Alex Panchula, and Yiming Huai

Appl. Phys. Lett. 87, 232502 (2005); http://dx.doi.org/10.1063/1.2139849 (3 pages) | Cited 75 times

Online Publication Date: 1 December 2005

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We present spin transfer switching results for MgO based magnetic tunneling junctions (MTJs) with large tunneling magnetoresistance (TMR) ratio of up to 150% and low intrinsic switching current density of 2–3×106 A/cm2. The switching data are compared to those obtained on similar MTJ nanostructures with AlOx barrier. It is observed that the switching current density for MgO based MTJs is 3 to 4 times smaller than that for AlOx based MTJs, and that can be attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In addition, we report a qualitative study of TSP for a set of samples, ranging from 0.22 for AlOx to 0.46 for MgO based MTJs, and that shows the TSP (at finite bias) responsible for the current-driven magnetization switching is suppressed as compared to zero-bias tunneling spin polarization determined from TMR.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials

Tuning porosity of YBa2Cu3O7−δ vicinal films by insertion of Y2BaCuO5 nanoparticles

R. L. S. Emergo, J. Z. Wu, T. J. Haugan, and P. N. Barnes

Appl. Phys. Lett. 87, 232503 (2005); http://dx.doi.org/10.1063/1.2140467 (3 pages) | Cited 18 times

Online Publication Date: 1 December 2005

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High critical current density (Jc) is the most critical specification for high-temperature-superconductor-coated conductors as required by numerous electric power-related applications. This has motivated an intensive research effort on the effects of microstructure on Jc. By growing YBa2Cu3O7−δ (YBCO) films at a small vicinal angle [ R. L. S. Emergo, J. Z. Wu, T. Aytug, and D. K. Christen, Appl. Phys. Lett. 85, 618 (2004) ] we have recently obtained a highly porous structure in these films accompanied with a significantly enhanced Jc. This result raises a challenging question on whether the porosity can be tailored in YBCO films to allow a higher Jc. In this study, we have explored the insertion of Y2BaCuO5 (211) nanoparticles in vicinal YBCO thick films to alter the strain at the nanometer scale; a nearly doubled pore density was obtained. A further improved Jc as the consequence of the enhanced pore density in these films suggests a direct correlation between microstructure and Jc and projects an even higher Jc in YBCO films with microstructure engineered optimally at a nanometer scale.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology

Evidence for hot electron magnetocurrent in a double barrier tunnel junction device

S. Ladak and R. J. Hicken

Appl. Phys. Lett. 87, 232504 (2005); http://dx.doi.org/10.1063/1.2140480 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2005

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Hot electron transport has been studied in three terminal Ta/TaOx/Co/AlOx/Ni81Fe19 structures fabricated by magnetron sputtering through shadow masks. With the Co base and Ta collector connected together via a small resistor, the collector current contains contributions first from hot electrons injected from the Ni81Fe19 emitter, and second from a geometrical artifact that leads to tunneling from the Fermi level in the base. Both sources of collector current lead to a room temperature magnetocurrent effect. The hot electron contribution begins to dominate as the emitter-base voltage −Veb exceeds 0.3 V.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.20.Ht High-field and nonlinear effects
73.21.Ac Multilayers
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