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19 Dec 2011

Volume 99, Issue 25, Articles (25xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 253701 (2011); http://dx.doi.org/10.1063/1.3666819 (3 pages)

Jun Huang, Hui Li, Wei Chen, Guo-Hua Lv, Xing-Quan Wang, Guo-Ping Zhang, Kostya Ostrikov, Peng-Ye Wang, and Si-Ze Yang
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X-ray magnetic circular dichroism of ferromagnetic Co4N epitaxial films on SrTiO3(001) substrates grown by molecular beam epitaxy

Keita Ito, Kazunori Harada, Kaoru Toko, Mao Ye, Akio Kimura, Yukiharu Takeda, Yuji Saitoh, Hiro Akinaga, and Takashi Suemasu

Appl. Phys. Lett. 99, 252501 (2011); http://dx.doi.org/10.1063/1.3670353 (3 pages) | Cited 3 times

Online Publication Date: 19 December 2011

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5-nm thick Co4N layers capped with 3-nm thick Au layers were grown epitaxially on SrTiO3(001) substrates by molecular beam epitaxy using solid Co and a radio-frequency NH3 plasma. Spin and orbital magnetic moments of the Co4N layers were estimated using x-ray magnetic circular dichroism (XMCD) measurements at 300 K. The site-averaged Co 3d spin magnetic moment is evaluated to be about 1.4 μB, which is smaller than that predicted theoretically (1.58 μB). The element-specific XMCD intensities for the Co L3 edge and N K edge show that the magnetic moment is induced at the N atoms.
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78.20.Ls Magneto-optical effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.aj Insulators
75.50.Dd Nonmetallic ferromagnetic materials

Correlation between the ferromagnetic metal percolation and the sign evolution of angular dependent magnetoresistance in Pr0.7Ca0.3MnO3 film

Y. Q. Zhang, H. Meng, X. W. Wang, J. J. Liu, J. Du, and Z. D. Zhang

Appl. Phys. Lett. 99, 252502 (2011); http://dx.doi.org/10.1063/1.3670399 (4 pages)

Online Publication Date: 20 December 2011

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Angular dependent magnetoresistance (AMR) phenomena in Pr0.7Ca0.3MnO3 film have been investigated. A transition between cos2θ dependent AMR in an insulating state at low fields and sin2θ dependent AMR in a metal state at high fields is observed at intermediate fields, depending on the temperature and/or strength of an applied magnetic field. Although the AMR sign evolution process from cos2θ dependence to sin2θ dependence at low temperature is different from that at high temperature due to existence of ferromagnetic insulator besides charge ordering antiferromagnetic insulator, we believe that such AMR sign evolutions are closely related with magnetic-field-induced ferromagnetic metal percolation behavior.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Ee Antiferromagnetics
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

(001) textured L10-FePt pseudo spin valve with TiN spacer

P. Ho, G. C. Han, K. H. He, G. M. Chow, and J. S. Chen

Appl. Phys. Lett. 99, 252503 (2011); http://dx.doi.org/10.1063/1.3671988 (4 pages) | Cited 2 times

Online Publication Date: 21 December 2011

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TiN was investigated as a potential spacer material in L10-FePt based pseudo spin valves (PSV). PSVs with the structure MgO/L10-Fe50Pt50 (20 nm)/TiN (5 nm)/L10-Fe50Pt50 (x nm) were fabricated, where x was varied from 5 to 20 nm. The highest giant magnetoresistance (GMR) ratio of 0.61% was obtained for the PSV with a top L10-FePt thickness of 20 nm. Contributions to the GMR arose from both the spin dependent scattering at the FePt/TiN interfaces and domain wall resistivity. Magnon magnetoresistance was also observed in the fabricated PSVs.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
75.60.Ch Domain walls and domain structure
68.55.-a Thin film structure and morphology

Unusual magnetic anisotropy in the ferromagnetic shape-memory alloy Ni50Fe23Ga27

J. F. Qian (钱金凤), E. K. Liu (刘恩克), L. Feng (冯琳), W. Zhu (朱伟), G. J. Li (李贵江), W. H. Wang (王文洪), G. H. Wu (吴光恒), Z. W. Du (杜志伟), and X. Fu (付新)

Appl. Phys. Lett. 99, 252504 (2011); http://dx.doi.org/10.1063/1.3671666 (3 pages)

Online Publication Date: 21 December 2011

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Unusual magnetic anisotropy of the ferromagnetic shape-memory alloy Ni50Fe23Ga27 has been observed. The anisotropy of the austenite becomes very large, even larger than that of the martensite in ribbon samples. Lowering the temperature from 300 K to 80 K, the saturation field of the austenite is dramatically increased from 200 Oe up to 6 kOe. This high-anisotropy behavior clearly highlights the demagnetization effect of the martensitic transformation. The physical mechanism is attributed to a collective effect coming from the atomic disorder, the premartensitic transformation, and the off-stoichiometric Ga-rich composition of the alloys.
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75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.60.-d Domain effects, magnetization curves, and hysteresis
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
61.66.Bi Elemental solids
61.66.Dk Alloys

Observations of laser induced magnetization dynamics in Co/Pd multilayers with coherent x-ray scattering

B. Wu, D. Zhu, Y. Acremann, T. A. Miller, A. M. Lindenberg, O. Hellwig, J. Stöhr, and A. Scherz

Appl. Phys. Lett. 99, 252505 (2011); http://dx.doi.org/10.1063/1.3670305 (3 pages) | Cited 2 times

Online Publication Date: 22 December 2011

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We report on time-resolved coherent x-ray scattering experiments of laser induced magnetization dynamics in Co/Pd multilayers with a high repetition rate optical pump x-ray probe setup. Starting from a multi-domain ground state, the magnetization is uniformly reduced after excitation by an intense 50 fs laser pulse. Using the normalized time correlation, we study the magnetization recovery on a picosecond timescale. The dynamic scattering intensity is separated into an elastic portion at length scales above 65 nm, which retains memory of the initial domain magnetization, and a fluctuating portion at smaller length scales corresponding to domain boundary motion during recovery.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.78.Fg Dynamics of domain structures
75.60.Ch Domain walls and domain structure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.70.Ck X-ray scattering

Large coercivity in nanostructured rare-earth-free MnxGa films

T. J. Nummy, S. P Bennett, T. Cardinal, and D. Heiman

Appl. Phys. Lett. 99, 252506 (2011); http://dx.doi.org/10.1063/1.3671329 (3 pages) | Cited 6 times

Online Publication Date: 22 December 2011

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The magnetic hysteresis of MnxGa films exhibit remarkably large coercive fields as high as μoHC = 2.5 T when fabricated with nanoscale particles of a suitable size and orientation. This coercivity is an order of magnitude larger than in well-ordered epitaxial film counterparts and bulk materials. The enhanced coercivity is attributed to the combination of large magnetocrystalline anisotropy and ∼50-100 nm size nanoparticles. The large coercivity is also replicated in the electrical properties through the anomalous Hall effect. The magnitude of the coercivity approaches that found in rare-earth magnets, making them attractive for rare-earth-free magnet applications.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.22.-f Electronic structure of nanoscale materials and related systems
75.30.Gw Magnetic anisotropy
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Origin of the collapse of tunnel magnetoresistance at high annealing temperature in CoFeB/MgO perpendicular magnetic tunnel junctions

H. D. Gan, H. Sato, M. Yamanouchi, S. Ikeda, K. Miura, R. Koizumi, F. Matsukura, and H. Ohno

Appl. Phys. Lett. 99, 252507 (2011); http://dx.doi.org/10.1063/1.3671669 (3 pages) | Cited 4 times

Online Publication Date: 23 December 2011

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We have investigated a tunnel magnetoresistance (TMR) ratio of CoFeB/MgO perpendicular magnetic tunnel junctions (p-MTJs) with a 40 nm diameter as a function of an annealing temperature Ta. The TMR ratio at room temperature (RT) increases with increasing Ta and reaches 149% at Ta = 350 °C, and further increase of Ta results in a strong reduction of the TMR ratio, i.e., 2% at Ta = 400 °C. The temperature dependence of the junction resistance versus magnetic field loops reveals that the reduced TMR ratio at RT is due to the disappearance of a stable antiparallel magnetization configuration. We find that reduction of dipole coupling restores the TMR ratio.
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75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
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