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15 Oct 2012

Volume 101, Issue 16, Articles (16xxxx)

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Appl. Phys. Lett. 101, 161105 (2012); http://dx.doi.org/10.1063/1.4744947 (4 pages)

Nan Niu, Tsung-Li Liu, Igor Aharonovich, Kasey J. Russell, Alexander Woolf, Thomas C. Sadler, Haitham A. R. El-Ella, Menno J. Kappers, Rachel A. Oliver, and Evelyn L. Hu
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Formation of nanoscale magnetic bubbles in ferromagnetic insulating manganite La7/8Sr1/8MnO3

T. Nagai, M. Nagao, K. Kurashima, T. Asaka, W. Zhang, and K. Kimoto

Appl. Phys. Lett. 101, 162401 (2012); http://dx.doi.org/10.1063/1.4760266 (5 pages)

Online Publication Date: 15 October 2012

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We have observed the response of spin arrangements to external magnetic fields in a multiorbital Mott insulator, ferromagnetic insulating manganite La7/8Sr1/8MnO3, by low-temperature in situ Lorentz microscopy. Magnetic fields normal to the plane of the thin-plate sample continuously change the width of domains in the serpentine-like domain structure, eventually giving rise to nanoscale elliptical magnetic bubbles of ∼200 nm major diameter at 3.6 kOe. The formation of these bubbles implies large magnetic anisotropy related to the orbital ordering and suggests the possibility of manipulating the bubbles using an electric field.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.Fk Domain structures in nanoparticles
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Gw Magnetic anisotropy

Spatially resolving variations in giant magnetoresistance, undetectable with four-point probe measurements, using infrared microspectroscopy

C. S. Kelley, S. M. Thompson, M. D. Illman, S. LeFrançois, and P. Dumas

Appl. Phys. Lett. 101, 162402 (2012); http://dx.doi.org/10.1063/1.4760282 (4 pages)

Online Publication Date: 16 October 2012

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Magnetorefractive infrared (IR) microspectroscopy is demonstrated to resolve spatial variations in giant magnetoresistance (GMR) and, by modelling, provide an insight into the origin of the variations. Spatial variations are shown to be masked in conventional four-point probe electrical or IR spectral measurements. IR microspectroscopy was performed at the SMIS beamline at the SOLEIL synchrotron, modified to enable measurements in magnetic fields. A GMR gradient was induced in a CoFe/Cu multilayer sample by annealing in a temperature gradient. Modelling revealed that variations in GMR at 900 Oe could be attributed to local variations in interlayer coupling locally changing the switching field.
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81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
78.30.Er Solid metals and alloys
78.20.Ls Magneto-optical effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.De Giant magnetoresistance

Room temperature ferromagnetic behavior in cluster free, Co doped Y2O3 dilute magnetic oxide films

C. N. Wu, S. Y. Huang, W. C. Lee, Y. H. Chang, T. S. Wu, Y. L. Soo, M. Hong, and J. Kwo

Appl. Phys. Lett. 101, 162403 (2012); http://dx.doi.org/10.1063/1.4760284 (5 pages) | Cited 1 time

Online Publication Date: 16 October 2012

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Extensive structural analysis and magnetic properties are reported on cluster free, dilute magnetic oxide of Co doped Y2O3 (Co:Y2O3) film by low temperature deposition and characterized by extended x-ray absorption fine structure, x-ray absorption near edge structure, magnetometer, and x-ray magnetic circular dichroism. Room temperature ferromagnetism was observed, and the saturation magnetic moment was modulated by oxygen vacancy concentration through post annealing process. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for this dilute magnetic oxide of medium band gap with low carrier concentration.
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75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
78.20.Ls Magneto-optical effects
75.30.Cr Saturation moments and magnetic susceptibilities
71.38.-k Polarons and electron-phonon interactions
73.61.Ng Insulators

Parallel-leaky capacitance equivalent circuit model for MgO magnetic tunnel junctions

Ajeesh M. Sahadevan, Kalon Gopinadhan, Charanjit S. Bhatia, and Hyunsoo Yang

Appl. Phys. Lett. 101, 162404 (2012); http://dx.doi.org/10.1063/1.4760279 (5 pages)

Online Publication Date: 17 October 2012

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The capacitance of MgO based magnetic tunnel junctions (MTJs) has been observed to be magnetic field dependent. We propose an equivalent circuit for the MTJs with a parallel-leaky capacitance (Cl) across the series combination of geometric and interfacial capacitance. The analysis of junctions with different tunneling magnetoresistance (TMR) values suggests higher Cl for low TMR junctions. Using Cole-Cole plots, the capacitive nature of MTJs is manifested. Fitting with Maxwell-Wagner capacitance model validates the RC parallel network model for MTJs and the extracted field dependent parameters match with the experimental values.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.20.My Galvanomagnetic and other magnetotransport effects

Metastable state in a shape-anisotropic single-domain nanomagnet subjected to spin-transfer-torque

Kuntal Roy, Supriyo Bandyopadhyay, and Jayasimha Atulasimha

Appl. Phys. Lett. 101, 162405 (2012); http://dx.doi.org/10.1063/1.4761250 (4 pages)

Online Publication Date: 17 October 2012

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We predict the existence of a metastable magnetization state in a single-domain nanomagnet with uniaxial shape anisotropy. It emerges when a spin-polarized current, which delivers a spin-transfer-torque possessing a field-like component, is injected into the nanomagnet. At a metastable state, the internal torque due to nanomagnet's shape anisotropy cancels the externally applied spin-transfer-torque and hence the net torque acting on the magnetization becomes zero. Therefore, it prevents spin-transfer-torque from switching the magnetization from one stable state along the easy axis to the other, even in the presence of room-temperature thermal fluctuations.
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75.30.Gw Magnetic anisotropy
75.78.Jp Ultrafast magnetization dynamics and switching
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Fk Domain structures in nanoparticles

Magnetocaloric properties of La(Fe,Si)13-based material and its hydride prepared by industrial mischmetal

L. F. Bao, F. X. Hu, L. Chen, J. Wang, J. R. Sun, and B. G. Shen

Appl. Phys. Lett. 101, 162406 (2012); http://dx.doi.org/10.1063/1.4760262 (5 pages)

Online Publication Date: 18 October 2012

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Here, we choose La-Ce-Pr-Nd industrial mischmetal with low purity as raw material to prepare La(Fe,Si)13-based magnetocaloric material and its hydride. It is demonstrated that the introduced impurities in the starting materials do not impair the formation of NaZn13-type structure. The multi-replacement of La by magnetic atoms Ce,Pr,Nd enhances Curie temperature TC while keeps the strong itinerant electron metamagnetic behavior. As a result, good magnetocaloric (MCE) properties appear in La0.7(Ce,Pr,Nd)0.3Fe11.6Si1.4 (LRFS) compound. The incorporation of interstitial H atom remarkably reduces hysteresis loss while increases TC to 314 K. The effective refrigeration capacity after deducting hysteresis can be increased by ∼128% upon H doping.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Hx Magnetic impurity interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
61.72.jj Interstitials

Dynamic spin injection into chemical vapor deposited graphene

A. K. Patra, S. Singh, B. Barin, Y. Lee, J.-H. Ahn, E. del Barco, E. R. Mucciolo, and B. Özyilmaz

Appl. Phys. Lett. 101, 162407 (2012); http://dx.doi.org/10.1063/1.4761932 (4 pages) | Cited 2 times

Online Publication Date: 19 October 2012

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We demonstrate dynamic spin injection into chemical vapor deposition (CVD) grown graphene by spin pumping from permalloy (Py) layers. Ferromagnetic resonance measurements at room temperature reveal a strong enhancement of the Gilbert damping at the Py/graphene interface, indeed exceeding that observed in Py/platinum interfaces. Similar results are also shown on Co/graphene layers. This enhancement in the Gilbert damping is understood as the consequence of spin pumping at the interface driven by magnetization dynamics. Our observations suggest a strong enhancement of spin-orbit coupling in CVD graphene, in agreement with earlier spin valve measurements.
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72.25.Mk Spin transport through interfaces
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Light-induced magnetization reversal of high-anisotropy TbCo alloy films

Sabine Alebrand, Matthias Gottwald, Michel Hehn, Daniel Steil, Mirko Cinchetti, Daniel Lacour, Eric E. Fullerton, Martin Aeschlimann, and Stéphane Mangin

Appl. Phys. Lett. 101, 162408 (2012); http://dx.doi.org/10.1063/1.4759109 (4 pages) | Cited 1 time

Online Publication Date: 19 October 2012

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multimedia

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Magnetization reversal using circularly polarized light provides a way to control magnetization without any external magnetic field and has the potential to revolutionize magnetic data storage. However, in order to reach ultra-high density data storage, high anisotropy media providing thermal stability are needed. Here, we evidence all-optical magnetization switching for different TbxCo1−x ferrimagnetic alloy compositions using fs- and ps-laser pulses and demonstrate all-optical switching for films with anisotropy fields reaching 6 T corresponding to anisotropy constants of 3 × 106 ergs/cm3. Optical magnetization switching is observed only for alloy compositions where the compensation temperature can be reached through sample heating.
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75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
81.40.Gh Other heat and thermomechanical treatments
78.66.Bz Metals and metallic alloys
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