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31 May 2010

Volume 96, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 96, 223101 (2010); http://dx.doi.org/10.1063/1.3439728 (3 pages)

Seokho Yun, Jeremy A. Bossard, Theresa S. Mayer, and Douglas H. Werner
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Enhanced low field magnetoresistance in nanocrystalline La0.7Sr0.3MnO3 synthesized on MgO nanowires

Z. Zhang, R. Ranjith, B. T. Xie, L. You, L. M. Wong, S. J. Wang, J. L. Wang, W. Prellier, Y. G. Zhao, and T. Wu

Appl. Phys. Lett. 96, 222501 (2010); http://dx.doi.org/10.1063/1.3432113 (3 pages) | Cited 13 times

Online Publication Date: 1 June 2010

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We report on the structure and transport properties of nanocrystalline manganite La0.7Sr0.3MnO3 (LSMO) synthesized on nanowires-engineered MgO substrates by pulsed laser deposition, which is compared with reference samples deposited directly on flat MgO substrates. Such LSMO/MgO nanocomposites show enhanced low field magnetoresistance, especially at low temperature, due to the dominant spin-polarized intergrain tunneling. This work suggests that growing on nanoengineered substrates is a viable route to achieve nanostructured materials with desired crystalline structure and physical properties.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.15.Fg Pulsed laser ablation deposition
61.46.Np Structure of nanotubes (hollow nanowires)

Controlled domain-wall injection in perpendicularly magnetized strips

R. Lavrijsen, J. H. Franken, J. T. Kohlhepp, H. J. M. Swagten, and B. Koopmans

Appl. Phys. Lett. 96, 222502 (2010); http://dx.doi.org/10.1063/1.3432703 (3 pages) | Cited 8 times

Online Publication Date: 1 June 2010

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For applications of domain wall (DW) motion in magnetic devices, it is vital to control the creation and position of the DW. We use Ga+ irradiation of Pt/Co/Pt strips to locally change the perpendicular magnetic anisotropy. This allows us to controllably inject DWs into a device at a tunable field. The observed initial linear decrease and subsequent increase in the DW injection field upon increasing irradiation dose are explained by micromagnetic simulations and an analytical one-dimensional model.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
75.78.Cd Micromagnetic simulations

Enhanced exchange anisotropy in IrMn/CoFeB systems and its correlation with uncompensated interfacial spins

Yuqing Du, Genhua Pan, Roy Moate, Hendrik Ohldag, Andras Kovacs, and Amit Kohn

Appl. Phys. Lett. 96, 222503 (2010); http://dx.doi.org/10.1063/1.3442480 (3 pages) | Cited 6 times

Online Publication Date: 1 June 2010

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Bottom pinned exchange bias systems of IrMn/CoFe and IrMn/CoFeB on CoFe seed layers were studied. Enhanced exchange anisotropy has been observed for IrMn/CoFeB samples annealed at 350 °C. The ferromagnetic and antiferromagnetic layers of both samples are polycrystalline and textured {110} for the CoFe and CoFeB, and {111} for IrMn. Results demonstrated that the enhanced exchange anisotropy in the IrMn/CoFeB system is closely associated with the increased uncompensated interfacial spins as evidenced by the enhanced Mn x-ray magnetic circular dichroism (XMCD) signal strength. A quantitative correlation between the Mn XMCD signal and the exchange anisotropy constant Jk was observed.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
81.40.Gh Other heat and thermomechanical treatments
75.50.Ee Antiferromagnetics
75.30.Gw Magnetic anisotropy

Electric field effect on magnetization at the Fe/MgO(001) interface

Manish K. Niranjan, Chun-Gang Duan, Sitaram S. Jaswal, and Evgeny Y. Tsymbal

Appl. Phys. Lett. 96, 222504 (2010); http://dx.doi.org/10.1063/1.3443658 (3 pages) | Cited 28 times

Online Publication Date: 2 June 2010

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Density-functional calculations are performed to explore magnetoelectric effects originating from the influence of an external electric field on magnetic properties of the Fe/MgO(001) interface. It is shown that the effect on the interface magnetization and magnetocrystalline anisotropy can be substantially enhanced if the electric field is applied across a dielectric material with a large dielectric constant. In particular, we predict an enhancement of the interface magnetoelectric susceptibility by a factor of the dielectric constant of MgO over that of the free standing Fe (001) surface. We also predict a significant effect of electric field on the interface magnetocrystalline anisotropy due to the change in the relative occupancy of the 3d-orbitals of Fe atoms at the Fe/MgO interface. These results may be interesting for technological applications such as electrically controlled magnetic data storage.
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75.85.+t Magnetoelectric effects, multiferroics
77.22.Ch Permittivity (dielectric function)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Emergence of ferromagnetism in antiferromagnetic TbMnO3 by epitaxial strain

X. Marti, V. Skumryev, C. Ferrater, M. V. García-Cuenca, M. Varela, F. Sánchez, and J. Fontcuberta

Appl. Phys. Lett. 96, 222505 (2010); http://dx.doi.org/10.1063/1.3443714 (3 pages) | Cited 12 times

Online Publication Date: 2 June 2010

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We show that in oxide thin films of spiral antiferromagnetic orthorhombic TbMnO3, ferromagnetism emerges resulting from epitaxially induced strain. The unit cell volume can be tuned (contracting up to a 2%) by varying thickness and deposition conditions; it is found that the ferromagnetic response correlates with the unit cell deformation. Such effect of strain on the magnetic properties turns out to be similar to that occurring in collinear orthorhombic antiferromagnets such as YMnO3. Owing to the intimate relationship between magnetic order and ferroelectricity in TbMnO3 these results may provide a new route to induce magnetoelectric coupling and tailor their ferroelectric response.
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75.70.Ak Magnetic properties of monolayers and thin films
68.60.Bs Mechanical and acoustical properties
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Determining magnetic nanoparticle size distributions from thermomagnetic measurements

R. S. DiPietro, H. G. Johnson, S. P. Bennett, T. J. Nummy, L. H. Lewis, and D. Heiman

Appl. Phys. Lett. 96, 222506 (2010); http://dx.doi.org/10.1063/1.3441411 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2010

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Thermomagnetic measurements are used to obtain the size distribution and anisotropy of magnetic nanoparticles. An analytical transformation method is described which utilizes temperature-dependent zero-field cooling magnetization data to provide a quantitative measurement of the average diameter and relative abundance of superparamagnetic nanoparticles. Applying this method to self-assembled MnAs nanoparticles in MnAs–GaAs composite films reveals a log-normal size distribution and reduced anisotropy for nanoparticles compared to bulk materials. This analytical technique holds promise for rapid assessment of the size distribution of an ensemble of superparamagnetic nanoparticles.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Gw Magnetic anisotropy
75.20.-g Diamagnetism, paramagnetism, and superparamagnetism

Magnetic properties and phase stability of L21 phase in Co2Mn(Ga1−xZx)(Z = Si, Ge, and Sn) Heusler alloys

A. Okubo, R. Y. Umetsu, K. Kobayashi, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 96, 222507 (2010); http://dx.doi.org/10.1063/1.3427431 (3 pages) | Cited 6 times

Online Publication Date: 3 June 2010

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For the Co2Mn(Ga1−xZx) (Z = Si, Ge, and Sn) Heusler alloys, the L21/B2 order-disorder transition temperature TtL21/B2, the Curie temperature TC, and the saturation magnetization Ms were determined. The TtL21/B2 for all the systems linearly increases with increasing x. Although the TtL21/B2 was not determined in the high x region because of melting of alloys, those of Co2MnGe and Co2MnSn could be estimated by extrapolation from the quaternary data. The Ms at 4.2 K and the TC increase with x, and the Ms for all the systems is in good agreement with the Slater Pauling rule.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.K- Solid-solid transitions
64.60.Cn Order-disorder transformations
75.40.-s Critical-point effects, specific heats, short-range order

Control of magnetic and electric responses with electric and magnetic fields in magnetoelectric heterostructures

J. Das, M. Li, S. S. Kalarickal, S. Altmannshofer, K. S. Buchanan, J. F. Li, and D. Viehland

Appl. Phys. Lett. 96, 222508 (2010); http://dx.doi.org/10.1063/1.3443715 (3 pages) | Cited 8 times

Online Publication Date: 4 June 2010

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This paper reports on the tuning of both magnetic and electric responses with electric and magnetic fields for metglas-Pb (Zr,Ti)O3 based magnetoelectric (ME) heterostructures that can be promising for communication and sensor applications. The hysteresis loop results indicate a change in the in-plane magnetization due to application of voltages that leads to a tuning of the ferromagnetic resonance frequency by up to about 210 MHz with electric field. Furthermore, these structures show a high ME voltage coefficient that results in the detection of a 2 nT ac magnetic field and a low noise floor.
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75.85.+t Magnetoelectric effects, multiferroics
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

The origin of large overestimation of the magnetic entropy changes calculated directly by Maxwell relation

Weibin Cui, Wei Liu, and Zhidong Zhang

Appl. Phys. Lett. 96, 222509 (2010); http://dx.doi.org/10.1063/1.3446843 (3 pages) | Cited 9 times

Online Publication Date: 4 June 2010

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By investigating the nature of the first-order magnetostructural phase transition, we point out the origin of large overestimation of magnetic entropy changes calculated by directly applying the Maxwell relation. Furthermore, if the mass variations in ferromagnetic and paramagnetic phases on temperature are taken into consideration in two-phase region, taking MnAsCx, (Mn, Al)As, and Mn0.994Fe0.004As compounds as example, based on the modified Maxwell relation, the large overestimation and discrepancy of magnetic entropy changes disappear. The magnetic entropy changes are equivalent with the values by Clausius–Claperyon equation, indicating the validity of this modified approach.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.Ck Nonmetals
65.40.gd Entropy
64.70.K- Solid-solid transitions
75.50.Dd Nonmetallic ferromagnetic materials
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