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2 Nov 2009

Volume 95, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 95, 183504 (2009); http://dx.doi.org/10.1063/1.3256223 (3 pages)

Hoon-Sik Kim, Sang Min Won, Young-Geun Ha, Jong-Hyun Ahn, Antonio Facchetti, Tobin J. Marks, and John A. Rogers
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Time domain analyses of the converse magnetoelectric effect in a multiferroic metallic glass-relaxor ferroelectric heterostructure

Yajie Chen, Anton L. Geiler, Trifon Fitchorov, Carmine Vittoria, and V. G. Harris

Appl. Phys. Lett. 95, 182501 (2009); http://dx.doi.org/10.1063/1.3258023 (3 pages) | Cited 17 times

Online Publication Date: 3 November 2009

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The dynamic time domain response of the converse magnetoelectric effect in a multiferroic Metglas®/Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) heterostructure, under the application of a square waveform electric field excitation of 8 kV/cm at a frequency of 0.4 Hz, is reported. The relaxation behavior followed a stretched power-law function allowing the calculation of an intrinsic time constant. Aging behavior of magnetoelectric coupling was observed after polarization switching of 1000 cycles. These phenomena are predominantly attributed to the temporal response of polarization within the PMN-PT crystal. Results elucidate the dynamic properties of relaxor-based multiferroic heterostructures and importantly define operational constraints for low frequency device operation.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
61.43.Fs Glasses

Giant tunneling magnetoresistance up to 330% at room temperature in sputter deposited Co2FeAl/MgO/CoFe magnetic tunnel junctions

Wenhong Wang, Hiroaki Sukegawa, Rong Shan, Seiji Mitani, and Koichiro Inomata

Appl. Phys. Lett. 95, 182502 (2009); http://dx.doi.org/10.1063/1.3258069 (3 pages) | Cited 36 times

Online Publication Date: 3 November 2009

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Magnetoresistance ratio up to 330% at room temperature (700% at 10 K) has been obtained in a spin-valve-type magnetic tunnel junction (MTJ) consisting of a full-Heusler alloy Co2FeAl electrode and a MgO tunnel barrier fabricated on a single crystal MgO (001) substrate by sputtering method. The output voltage of the MTJ at one-half of the zero-bias value was found to be as high as 425 mV, which is the largest reported to date in MTJs using Heusler alloy electrodes. The present finding suggests that Co2FeAl may be one of the most promising candidates for future spintronics devices applications.
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75.47.De Giant magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
81.15.Cd Deposition by sputtering
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Coengineering of ferroelectric and exchange bias properties in BiFeO3 based heterostructures

J. Allibe, I. C. Infante, S. Fusil, K. Bouzehouane, E. Jacquet, C. Deranlot, M. Bibes, and A. Barthélémy

Appl. Phys. Lett. 95, 182503 (2009); http://dx.doi.org/10.1063/1.3247893 (3 pages) | Cited 16 times

Online Publication Date: 3 November 2009

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The magnetoelectric coupling existing in some multiferroics may allow the low-power electrical control of spintronics devices. However, room temperature magnetoelectric multiferroics are extremely rare, an exception being BiFeO3, a ferroelectric antiferromagnet. To be used for electrically controllable spintronics, BiFeO3 has to be coupled with a ferromagnetic material through an interfacial exchange interaction, and carefully engineered to show minimum leakage. Here, we propose a Mn doped/undoped bilayer strategy that allows obtaining large exchange bias as well as low leakage. This is an important step toward the manipulation of a magnetization by an electric field in a vertical geometry.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Fg Pulsed laser ablation deposition
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.80.+q Magnetomechanical effects, magnetostriction
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Direct observation of individual Barkhausen avalanches in nucleation-mediated magnetization reversal processes

Mi-Young Im, Peter Fischer, Dong-Hyun Kim, and Sung-Chul Shin

Appl. Phys. Lett. 95, 182504 (2009); http://dx.doi.org/10.1063/1.3256188 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2009

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We report the scaling behavior of Barkhausen avalanches [ H. Barkhausen, Z. Phys. 20, 401 (1919) .] along the hysteresis loop of a CoCrPt alloy film with perpendicular magnetic anisotropy for every field step of 200 Oe. Individual Barkhausen avalanches are directly observed via soft x-ray microscopy with a spatial resolution of 15 nm. The Barkhausen avalanches exhibit a power-law scaling behavior, where the scaling exponent of the power-law distribution drastically changes from 1±0.04 to 1.47±0.03 as the applied field approaches the coercivity of the CoCrPt film. We infer that this is due to the coupling of adjacent domains.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.jd Thickness
68.37.Yz X-ray microscopy
75.70.Ak Magnetic properties of monolayers and thin films

Low-temperature magnetotransport behaviors of heavily Mn-doped (Ga,Mn)As films with high ferromagnetic transition temperature

L. Chen, S. Yan, P. F. Xu, J. Lu, W. Z. Wang, J. J. Deng, X. Qian, Y. Ji, and J. H. Zhao

Appl. Phys. Lett. 95, 182505 (2009); http://dx.doi.org/10.1063/1.3259821 (3 pages) | Cited 23 times

Online Publication Date: 5 November 2009

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We report the low-temperature magnetotransport behaviors of (Ga,Mn)As films with the nominal Mn concentration x larger than 10%. The ferromagnetic transition temperature TC can be enhanced to 191 K after postgrowth annealing (Ga,Mn)As with x = 20%. The temperature Tm, corresponding to the resistivity minimum in the curve of resistivity versus temperature at temperature below TC, depends on Mn concentration, annealing condition, and magnetic field. Moreover, we find that the variable-range hopping may be the main conductive mechanism when temperature is lower than Tm.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.50.Dd Nonmetallic ferromagnetic materials
73.61.Ey III-V semiconductors
75.50.Pp Magnetic semiconductors
61.72.U- Doping and impurity implantation
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Temperature- and magnetic-field-controlled magnetic pole reversal in a molecular magnetic compound

S. M. Yusuf, Amit Kumar, and J. V. Yakhmi

Appl. Phys. Lett. 95, 182506 (2009); http://dx.doi.org/10.1063/1.3259652 (3 pages) | Cited 8 times

Online Publication Date: 6 November 2009

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A highly reversible (bipolar) switching of magnetization in a Prussian blue type molecular magnet Cu0.73Mn0.77[Fe(CN)6]⋅zH2O using low magnetic fields is demonstrated. The studied molecular compound also shows both positive and negative magnetocaloric effects below its magnetic ordering temperature. A molecular field theory calculation has also been done to explain the observed temperature dependent magnetization reversal behavior. Possible applications of the magnetic pole reversal phenomenon in magnetoelectronic and magnetocaloric devices such as magnetic memory and magnetic cooling/heating based constant temperature bath have been revealed.
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75.60.Jk Magnetization reversal mechanisms
75.50.Xx Molecular magnets
75.30.Sg Magnetocaloric effect, magnetic cooling

Observation of asymmetrical pinning of domain walls in notched Permalloy nanowires using electron holography

Kai He, David J. Smith, and Martha R. McCartney

Appl. Phys. Lett. 95, 182507 (2009); http://dx.doi.org/10.1063/1.3261753 (3 pages) | Cited 6 times

Online Publication Date: 6 November 2009

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Field-driven domain-wall motion and pinning in notched Permalloy nanowires have been observed using electron holography and Lorentz microscopy. Transverse domain walls (TDWs) were identified and different aspects of their behavior, including nucleation, injection, pinning, and depinning, were studied. The relative chirality (i.e., sense of field rotation) of the notch and the nucleation pad had a major influence in determining the TDW propagation: the walls were preferentially pinned for a notch of opposite chirality, but simply passed through when the notch had the same chirality. This asymmetrical TDW pinning accounts for the observed asymmetrical hysteresis hoop.
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75.60.Ch Domain walls and domain structure
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

All-optical detection of phase fronts of propagating spin waves in a Ni81Fe19 microstripe

K. Vogt, H. Schultheiss, S. J. Hermsdoerfer, P. Pirro, A. A. Serga, and B. Hillebrands

Appl. Phys. Lett. 95, 182508 (2009); http://dx.doi.org/10.1063/1.3262348 (3 pages) | Cited 15 times

Online Publication Date: 6 November 2009

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We present the determination of the wavelength and phase of propagating spin waves in magnetic microstructures made of Ni81Fe19 using the shorted end of a coplanar waveguide for local excitation. The spin wave characteristics have been measured by phase resolved Brillouin light scattering microscopy. This recently developed technique allows for the unambiguous experimental visualization of the phase structure of propagating spin waves and is employed here to magnetic microstructures. The results show an excellent agreement with the theoretically predicted spin-wave dispersion relations.
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84.40.Az Waveguides, transmission lines, striplines
75.30.Ds Spin waves
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Magnetic and conductive dead layer at the La0.67Ca0.33MnO3–SrTiO3:Nb interface

S. Liang, J. R. Sun, J. Wang, and B. G. Shen

Appl. Phys. Lett. 95, 182509 (2009); http://dx.doi.org/10.1063/1.3262951 (3 pages) | Cited 4 times

Online Publication Date: 6 November 2009

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Interfacial properties of the La0.67Ca0.33MnO3 films grown on SrTiO3 and SrTiO3:Nb, respectively, have been experimentally studied. An interface layer, ∼ 13 or ∼ 4.4 nm for the films on SrTiO3 or SrTiO3:Nb, with degenerated magnetic/conductive properties is found in the film. The most remarkable result is the significantly different layer width on different substrates. The built-in electric field yielded by charge exchange may be responsible for the layer shrinkage in La0.67Ca0.33MnO3/SrTiO3:Nb. A depression of this layer by magnetic field is also observed and ascribed to field-induced enhancement of the double exchange between Mn ions.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.61.Ng Insulators
68.55.aj Insulators

Spin-dependent intergranular transport in highly spin-polarized Co1−xFexS2 thin films

M. Manno, R. Frakie, B. Bolon, and C. Leighton

Appl. Phys. Lett. 95, 182510 (2009); http://dx.doi.org/10.1063/1.3262958 (3 pages) | Cited 1 time

Online Publication Date: 6 November 2009

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Magnetic and magnetotransport measurements on polycrystalline thin film Co1−xFexS2, a system that exhibits tunable conduction electron spin polarization in bulk, are reported. The films exhibit a low field hysteretic magnetoresistance (MR) due to spin-dependent intergranular tunneling, thus providing a simple probe of the spin polarization. The MR increases rapidly with x, saturating as the magnetization reaches 1.0μB/Co, demonstrating that high, doping tunable, spin polarization can be readily achieved in thin films synthesized by simple methods. Quantitative estimates yield spin polarizations as high as 90%.
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72.25.Dc Spin polarized transport in semiconductors
75.50.Pp Magnetic semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Le Other inorganic semiconductors

X-ray magnetic circular dichroism studies of Fe doped fullerene and highly oriented pyrolytic graphite

Amit Kumar, P. Thakur, N. B. Brookes, and D. K. Avasthi

Appl. Phys. Lett. 95, 182511 (2009); http://dx.doi.org/10.1063/1.3258656 (3 pages) | Cited 2 times

Online Publication Date: 6 November 2009

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We report the x-ray magnetic circular dichroism (XMCD) studies on Fe doped fullerene thin film and bulk highly oriented pyrolytic graphite. The element-specific hysteresis curves were recorded by measuring the XMCD at the Fe L3 edge as a function of the applied field strength at different temperatures. These investigations suggest that Fe doped fullerene is ferromagnetic at room temperature, while Fe atoms are driven to a nonmagnetic/paramagnetic state with the interaction of graphite matrix.
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78.20.Ls Magneto-optical effects
61.72.up Other materials
75.20.Ck Nonmetals
75.50.Dd Nonmetallic ferromagnetic materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
75.70.Ak Magnetic properties of monolayers and thin films
78.66.Tr Fullerenes and related materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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