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4 Apr 2011

Volume 98, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 98, 141903 (2011); http://dx.doi.org/10.1063/1.3548546 (3 pages)

H. Hattab, A. T. N’Diaye, D. Wall, G. Jnawali, J. Coraux, C. Busse, R. van Gastel, B. Poelsema, T. Michely, F.-J. Meyer zu Heringdorf, and M. Horn-von Hoegen
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Ballistic (precessional) contribution to the conventional magnetic switching

Ya. B. Bazaliy and Andrzej Stankiewicz

Appl. Phys. Lett. 98, 142501 (2011); http://dx.doi.org/10.1063/1.3570635 (3 pages) | Cited 3 times

Online Publication Date: 4 April 2011

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We consider a magnetic moment with an easy axis anisotropy energy, switched by an external field applied along this axis. Additional small, time-independent bias field is applied perpendicular to the axis. It is found that the magnet’s switching time is a non-monotonic function of the rate at which the field is swept from “up” to “down.” Switching time exhibits a minimum at a particular optimal sweep time. This unusual behavior is explained by the admixture of a ballistic (precessional) rotation of the moment caused by the perpendicular bias field in the presence of a variable switching field. We derive analytic expressions for the optimal switching time, and for the entire dependence of the switching time on the field sweep time. The existence of the optimal field sweep time has important implications for the optimization of magnetic memory devices.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.60.-d Domain effects, magnetization curves, and hysteresis
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy

The origin of different magnetic properties in nanosized Ca0.82La0.18MnO3: Wires versus particles

Yang Wang and Hong Jin Fan

Appl. Phys. Lett. 98, 142502 (2011); http://dx.doi.org/10.1063/1.3575571 (3 pages) | Cited 8 times

Online Publication Date: 4 April 2011

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A comparative investigation has been conducted on the nanowires and nanoparticles (both in the size range of 20–35 nm) of Ca0.82La0.18MnO3, finding that the nanowires have similar magnetic properties to the bulk, whereas the nanoparticles behave evidently different. In the nanoparticles, charge ordering and antiferromagnetic phase disappear; instead, a ferromagnetic transition is observed. Analysis of the crystal structure indicates that, for nanosized manganite systems, whether charge ordering is suppressed and ferromagnetism is developed as the size scales down depends on the level of intrinsic structural distortions; nanodimensional effect or surface effect is not determinant.
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75.75.-c Magnetic properties of nanostructures
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.25.Dk Orbital, charge, and other orders, including coupling of these orders
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Observation of spin filtering in magnetic insulator contacts to silicon

Martina Müller, Martina Luysberg, and Claus M. Schneider

Appl. Phys. Lett. 98, 142503 (2011); http://dx.doi.org/10.1063/1.3572016 (3 pages) | Cited 2 times

Online Publication Date: 5 April 2011

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The magnetic insulator EuS is used to create a spin-selective and conductivity-matched tunnel contact to silicon, in analogy to a conventional ferromagnetic metal/semiconductor configuration employed for spin injection. The spin filter efficiency of such a magnetic “spin filter” tunnel barrier is quantified using an adjacent Co ferromagnetic electrode as spin detector in a spin valve-type structure. This previously unobserved magnetoresistance effect demonstrates the efficient spin-polarizing nature of magnetic semiconductors on silicon and its prospective functionality as spin injectors/detectors in hybrid semiconductor devices.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
75.50.Pp Magnetic semiconductors

Magnetoresistance signature of resonant states in electromigrated Ni nanocontacts

J.-B. Beaufrand, J.-F. Dayen, N. T. Kemp, A. Sokolov, and B. Doudin

Appl. Phys. Lett. 98, 142504 (2011); http://dx.doi.org/10.1063/1.3576939 (3 pages)

Online Publication Date: 6 April 2011

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Fundamental insight is reported into magnetoresistance properties of ballistic-type atomic size Ni nanojunctions obtained at low temperatures. Feedback-controlled electromigration was used to reveal the ballistic nature of the transport and stabilize samples of conductance values in the range of G0 (G0 = 2e2/h). Bias voltage dependent measurements identify a clear magnetoresistance fingerprint of resonant tunneling, revealing that localized states in the nanojunctions can be responsible for nonlinear behavior in the IV curves and the related magnetoresistance properties.
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75.47.Np Metals and alloys
73.63.Rt Nanoscale contacts
73.23.Ad Ballistic transport
66.30.Qa Electromigration

Current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire

T. Suzuki, S. Fukami, N. Ishiwata, M. Yamanouchi, S. Ikeda, N. Kasai, and H. Ohno

Appl. Phys. Lett. 98, 142505 (2011); http://dx.doi.org/10.1063/1.3579155 (3 pages) | Cited 8 times

Online Publication Date: 8 April 2011

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The current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire was investigated. A threshold field decrease of 6.4 kOe/mA was observed by measuring the threshold field of Hall resistance versus the magnetic field curve with various bias currents. The decrease was probably caused by the in-plane effective field, mainly due to the Rashba effect. The effective field of the Ta/CoFeB/MgO wire was smaller and opposite in direction compared to that of Pt/Co/AlOx previously reported.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Compact tunable sub-terahertz oscillators based on Josephson junctions

Fengbin Song (宋凤斌), Franz Müller, Thomas Scheller, Alexei Semenov, Ming He, Lan Fang, Heinz-Wilhelm Hübers, and Alexander M. Klushin

Appl. Phys. Lett. 98, 142506 (2011); http://dx.doi.org/10.1063/1.3576910 (3 pages) | Cited 3 times

Online Publication Date: 8 April 2011

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Essential applications of terahertz technology are urgently in need of compact, tunable solid-state continuous wave radiation sources. However, no satisfactory solution is yet available for the frequency range of up to approximately 1.0 THz. Here, we present coherent radiation from large series arrays of Josephson junctions between 0.1 and 0.25 THz with off-chip radiation power of 7 μW. Niobium junctions oscillate at 4.2 K and the detection has been done at room temperature. The well-known obstacle to impedance matching is overcome by utilizing the excited resonances in the junction substrates serving as dielectric resonator antennae.
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85.25.Cp Josephson devices
84.40.Ba Antennas: theory, components and accessories
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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