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4 Jul 2011

Volume 99, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 99, 011107 (2011); http://dx.doi.org/10.1063/1.3606505 (3 pages)

Kosei Ueno, Satoaki Takabatake, Ko Onishi, Hiroko Itoh, Yoshiaki Nishijima, and Hiroaki Misawa
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Magnetic field dependence of the maximum adiabatic temperature change

M. D. Kuz'min, K. P. Skokov, D. Yu. Karpenkov, J. D. Moore, M. Richter, and O. Gutfleisch

Appl. Phys. Lett. 99, 012501 (2011); http://dx.doi.org/10.1063/1.3607279 (3 pages) | Cited 9 times

Online Publication Date: 5 July 2011

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The field dependence of the maximum magnetocaloric ΔT-effect in ferromagnets with second-order phase transitions is studied by way of direct measurements. All studied materials are found to follow the formula ΔTmax = A(H+H0)2/3-AH02/3, where A and H0 are constants and H is the internal magnetic field. It is essential to distinguish the latter from external field Hext. The dependence of ΔTmax on Hext is qualitatively distinct, the difference being particularly pronounced in the low-field region. In the field range relevant to applications (0.1–2 T), ΔTmax follows a linear dependence on H2/3. It is proposed to use the slope of this dependence as a figure of merit of magnetic refrigerants.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

The perpendicular anisotropy of Co40Fe40B20 sandwiched between Ta and MgO layers and its application in CoFeB/MgO/CoFeB tunnel junction

W. X. Wang, Y. Yang, H. Naganuma, Y. Ando, R. C. Yu, and X. F. Han

Appl. Phys. Lett. 99, 012502 (2011); http://dx.doi.org/10.1063/1.3605564 (3 pages) | Cited 14 times

Online Publication Date: 5 July 2011

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Magnetic anisotropy of Co40Fe40B20 thin films sandwiched between Ta and MgO layers was investigated. Magnetic properties of CoFeB layers deposited on top and bottom of MgO layer are different. The thickness of the CoFeB layer and annealing temperature are the critical parameters to achieve and keep the perpendicular magnetic anisotropy. The phase diagram of perpendicular anisotropic strength of CoFeB layers on annealing temperatures and thicknesses of CoFeB layers is observed. According to phase diagrams, perpendicular CoFeB/MgO/CoFeB tunnel junctions were fabricated, and tunneling magnetoresistance (TMR) ratio was higher than 30% at low temperatures.
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75.30.Gw Magnetic anisotropy
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Damping phenomena in Co90Fe10/Ni multilayers and alloys

Justin M. Shaw, Hans T. Nembach, and T. J. Silva

Appl. Phys. Lett. 99, 012503 (2011); http://dx.doi.org/10.1063/1.3607278 (3 pages) | Cited 6 times

Online Publication Date: 6 July 2011

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We used perpendicular ferromagnetic resonance to measure the damping parameter in Co90Fe10/Ni multilayers over a wide range of layer thicknesses. The magnetic anisotropy within this range varied from in-plane to out-of-plane. We measured (Co90Fe10)xNi1−x alloys of identical thicknesses over the same compositional range of Co90Fe10 and Ni in order to isolate the influence of the multilayer structure. The damping parameter varied from 0.004 to 0.030 and depended only on the relative amounts of Co90Fe10 and Ni and was independent of the magnetic anisotropy and layer structure.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

The effect of particle size on coercivity and crystallinity of SmCo5

C. H. Chen, S. J. Knutson, Y. Shen, R. A. Wheeler, J. C. Horwath, and P. N. Barnes

Appl. Phys. Lett. 99, 012504 (2011); http://dx.doi.org/10.1063/1.3607958 (3 pages) | Cited 5 times

Online Publication Date: 6 July 2011

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It is observed a turning point in the particle size for which the coercivity Hci of a Sm-Co alloy reaches a peak. Using a broad size range from 20 nm to 5 mm, the turning point of the flake thickness for SmCo5 nanoflakes is determined in the range of 100–180 nm with Hci peak at ∼20 kOe. A lower coercivity at a particle size well below the turning point is likely related to a more detailed nanoscale morphology that controls coercivity. The effect of particle size on crystallinity for high energy milled powder is also discussed with four observations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials

Resonant frequency multiplication in microscopic magnetic dots

V. E. Demidov, H. Ulrichs, S. Urazhdin, S. O. Demokritov, V. Bessonov, R. Gieniusz, and A. Maziewski

Appl. Phys. Lett. 99, 012505 (2011); http://dx.doi.org/10.1063/1.3609011 (3 pages) | Cited 3 times

Online Publication Date: 7 July 2011

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We demonstrate the phenomenon of nonlinear frequency multiplication in sub-micrometer Permalloy dots. The efficiency of multiplication is strongly enhanced when the harmonic is resonant with the normal dynamical modes of the dot. We find that the characteristics of resonant enhancement are dependent on the spatial symmetry of the dynamical mode and are different for the double- and the triple-frequency harmonics. The resonant frequency tripling is particularly efficient, providing a practical route for the implementation of microscopic integrated microwave frequency multipliers.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
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