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1 Oct 2012

Volume 101, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 101, 141101 (2012); http://dx.doi.org/10.1063/1.4742864 (4 pages)

Po-Hsun Huang, Michael Ian Lapsley, Daniel Ahmed, Yuchao Chen, Lin Wang, and Tony Jun Huang
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Exchange bias and memory effect in double perovskite Sr2FeCoO6

R. Pradheesh, Harikrishnan S. Nair, V. Sankaranarayanan, and K. Sethupathi

Appl. Phys. Lett. 101, 142401 (2012); http://dx.doi.org/10.1063/1.4756792 (4 pages)

Online Publication Date: 1 October 2012

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We report on the observation of exchange bias (EB) and memory effect in double perovskite Sr2FeCoO6. Antiphase boundaries between the ferromagnetic and the antiferromagnetic regions in the disordered glassy phase are assumed as responsible for the observed effect, which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass (SG) phase itself is characterized through memory, ageing, and magnetic relaxation experiments. The spin glass transition temperature, Tg, versus Hdc2/3 follows the Almeida-Thouless line yielding a freezing temperature, Tf = 73K. Time-dependent magnetic relaxation studies reveal the magnetization dynamics of the underlying glassy phase in this double perovskite.
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75.30.Et Exchange and superexchange interactions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.78.-n Magnetization dynamics

Dynamic response of exchange bias in graphene nanoribbons

S. Narayana Jammalamadaka, S. S. Rao, J. Vanacken, V. V. Moshchalkov, Wei Lu, and J. M. Tour

Appl. Phys. Lett. 101, 142402 (2012); http://dx.doi.org/10.1063/1.4755840 (5 pages)

Online Publication Date: 1 October 2012

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The dynamics of magnetic hysteresis, including the training effect and the field sweep rate dependence of the exchange bias, is experimentally investigated in exchange-coupled potassium split graphene nanoribbons (GNRs). We find that, at low field sweep rate, the pronounced absolute training effect is present over a large number of cycles. This is reflected in a gradual decrease of the exchange bias with the sequential field cycling. However, at high field sweep rate above 0.5 T/min, the training effect is not prominent. With the increase in field sweep rate, the average value of exchange bias field grows and is found to follow power-law behavior. The response of the exchange bias field to the field sweep rate variation is linked to the difference in the time it takes to perform a hysteresis loop measurement compared with the relaxation time of the anti-ferromagnetically aligned spins. The present results may broaden our current understanding of magnetism of GNRs and would be helpful in establishing the GNRs-based spintronic devices.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.Jn Dynamics of magnetic nanoparticles
75.30.Et Exchange and superexchange interactions

Perpendicular magnetic anisotropy of cobalt films intercalated under graphene

N. Rougemaille, A. T. N'Diaye, J. Coraux, C. Vo-Van, O. Fruchart, and A. K. Schmid

Appl. Phys. Lett. 101, 142403 (2012); http://dx.doi.org/10.1063/1.4749818 (3 pages)

Online Publication Date: 2 October 2012

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Magnetic properties of nanometer-thick Co films intercalated at the graphene/Ir(111) interface are investigated using spin-polarized low-energy electron microscopy and Auger electron spectroscopy. We show that the graphene top layer promotes perpendicular magnetic anisotropy in the Co film underneath, even for relatively thick intercalated deposits. The magnetic anisotropy energy is significantly larger for the graphene/Co interface than for the free Co surface. Hybridization of the graphene and Co electron orbitals is believed to be at the origin of the observed perpendicular magnetic anisotropy.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
79.20.Fv Electron impact: Auger emission

Investigation of room temperature ferromagnetism of 3C-SiC by vanadium carbide doping

Hui Wang, Cheng-Feng Yan, Hai-Kuan Kong, Jian-Jun Chen, Jun Xin, and Er-Wei Shi

Appl. Phys. Lett. 101, 142404 (2012); http://dx.doi.org/10.1063/1.4756939 (4 pages) | Cited 3 times

Online Publication Date: 2 October 2012

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Undoped and vanadium carbide (VC) doped 3C-SiC powders have been prepared, and an in-depth study is performed on the VC-doping dependence of room temperature ferromagnetism (FM). It is demonstrated that the FM originates in vacancy defects. The saturation magnetization (Ms) of VC is about 800 times than that of undoped 3C-SiC, while the Ms of VC-doped 3C-SiC is even smaller than that of the undoped one. The increase of doping concentration would result in the decrease of vacancy concentration and the increase of carrier concentration, suggesting that the FM of 3C-SiC is related to both vacancy and carrier concentrations.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.up Other materials
72.20.Fr Low-field transport and mobility; piezoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials

Single particle demultiplexer based on domain wall conduits

A. Torti, V. Mondiali, A. Cattoni, M. Donolato, E. Albisetti, A. M. Haghiri-Gosnet, Paolo Vavassori, and R. Bertacco

Appl. Phys. Lett. 101, 142405 (2012); http://dx.doi.org/10.1063/1.4755785 (5 pages)

Online Publication Date: 2 October 2012

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The remote manipulation of micro and nano-sized magnetic particles carrying molecules or biological entities over a chip surface is of paramount importance for future on-chip applications in biology and medicine. In this paper, we present a method for the on-chip demultiplexing of individual magnetic particles using bifurcated magnetic nano-conduits for the propagation of constrained domain walls (DWs). We demonstrate that the controlled injection and propagation of a domain wall in a bifurcation allow capturing, transporting, and sorting a single magnetic particle between two predefined paths. The cascade of n levels of such building blocks allows for the implementation of a variety of complex sorting devices as, e.g., a demultiplexer for the controlled sorting among 2n paths.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
87.85.Rs Nanotechnologies-applications

Bit error rate investigation of spin-transfer-switched magnetic tunnel junctions

Zihui Wang, Yuchen Zhou, Jing Zhang, and Yiming Huai

Appl. Phys. Lett. 101, 142406 (2012); http://dx.doi.org/10.1063/1.4756787 (4 pages) | Cited 1 time

Online Publication Date: 3 October 2012

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A method is developed to enable a fast bit error rate (BER) characterization of spin-transfer-torque magnetic random access memory magnetic tunnel junction (MTJ) cells without integrating with complementary metal-oxide semiconductor circuit. By utilizing the reflected signal from the devices under test, the measurement setup allows a fast measurement of bit error rates at >106, writing events per second. It is further shown that this method provides a time domain capability to examine the MTJ resistance states during a switching event, which can assist write error analysis in great detail. BER of a set of spin-transfer-torque MTJ cells has been evaluated by using this method, and bit error free operation (down to 10−8) for optimized in-plane MTJ cells has been demonstrated.
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75.70.Ak Magnetic properties of monolayers and thin films
02.50.-r Probability theory, stochastic processes, and statistics
02.60.-x Numerical approximation and analysis
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Magnetization of 2.6 T in gadolinium thin films

G. Scheunert, W. R. Hendren, C. Ward, and R. M. Bowman

Appl. Phys. Lett. 101, 142407 (2012); http://dx.doi.org/10.1063/1.4757126 (4 pages) | Cited 3 times

Online Publication Date: 3 October 2012

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See Also: Erratum

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There is renewed interest in rare-earth elements and gadolinium in particular for a range of studies in coupling physics and applications. However, it is still apparent that synthesis impacts understanding of the intrinsic magnetic properties of thin gadolinium films, particularly for thicknesses of topicality. We report studies on 50 nm thick nanogranular polycrystalline gadolinium thin films on SiO2 wafers that demonstrate single-crystal like behavior. The maximum in-plane saturation magnetization at 4 K was found to be 4πMS4 K = (2.61 ± 0.26) T with a coercivity of HC4 K = (160 ± 5) Oe. A maximum Curie point of TC = (293 ± 2) K was measured via zero-field-cooled–field-cooled magnetization measurements in close agreement with values reported in bulk single crystals. Our measurements revealed magnetic transitions at T1 = (12 ± 2) K (as deposited samples) and T2 = (22 ± 2) K (depositions on heated substrates) possibly arising from the interaction of paramagnetic face-centred cubic grains with their ferromagnetic hexagonal close-packed counterparts.
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75.70.Ak Magnetic properties of monolayers and thin films
75.75.Cd Fabrication of magnetic nanostructures
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Interdependence of reversal asymmetry and training effect in Ir22Mn78/Ni81Fe19 bilayers probed with magnetoresistance

Himanshu Fulara, Sujeet Chaudhary, and Subhash C. Kashyap

Appl. Phys. Lett. 101, 142408 (2012); http://dx.doi.org/10.1063/1.4757603 (5 pages) | Cited 1 time

Online Publication Date: 4 October 2012

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Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establishes that the two distinct training mechanisms are operative. The first one is exhibited by an abrupt single cycle training effect and an accompanying pronounced reversal asymmetry, attributed to the presence of biaxial anisotropy in the IrMn layer. The second one displays a gradual cycling dependence due to thermal depinning of uncompensated antiferromagnetic spins.
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75.60.Jk Magnetization reversal mechanisms
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
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