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13 Aug 2012

Volume 101, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 101, 071104 (2012); http://dx.doi.org/10.1063/1.4742749 (4 pages)

Judson D. Ryckman and S. M. Weiss
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Damping modulated terahertz emission of ferromagnetic films excited by ultrafast laser pulses

Jian Shen, Xin Fan, Zhiyuan Chen, Matthew F. DeCamp, Huaiwu Zhang, and John Q. Xiao

Appl. Phys. Lett. 101, 072401 (2012); http://dx.doi.org/10.1063/1.4737400 (4 pages) | Cited 1 time

Online Publication Date: 13 August 2012

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Ultrafast demagnetization processes in ferromagnetic films have been shown to produce terahertz (THz) emission. We present an experimental demonstration that, following ultrafast optical excitation, the magnitude of terahertz electromagnetic pulses emitted from a ferromagnetic film is proportional to the Gilbert damping constant, which is conventionally used to describe the damping of magnetization precession. The damping of a ferromagnetic thin film is tuned by using an adjacent nonmagnetic layer, which does not change the magnetization and anisotropy of the ferromagnetic film, allowing an unambiguous determination of the relationship between the THz emission and the damping constant.
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78.70.Gq Microwave and radio-frequency interactions
78.47.J- Ultrafast spectroscopy (<1 psec)
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Non-volatile voltage control of magnetization and magnetic domain walls in magnetostrictive epitaxial thin films

D. E. Parkes, S. A. Cavill, A. T. Hindmarch, P. Wadley, F. McGee, C. R. Staddon, K. W. Edmonds, R. P. Campion, B. L. Gallagher, and A. W. Rushforth

Appl. Phys. Lett. 101, 072402 (2012); http://dx.doi.org/10.1063/1.4745789 (4 pages) | Cited 4 times

Online Publication Date: 13 August 2012

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We demonstrate reproducible voltage induced non-volatile switching of the magnetization in an epitaxial thin Fe81Ga19 film. Switching is induced at room temperature and without the aid of an external magnetic field. This is achieved by the modification of the magnetic anisotropy by mechanical strain induced by a piezoelectric transducer attached to the layer. Epitaxial Fe81Ga19 is shown to possess the favourable combination of cubic magnetic anisotropy and large magnetostriction necessary to achieve this functionality with experimentally accessible levels of strain. The switching of the magnetization proceeds by the motion of magnetic domain walls, also controlled by the voltage induced strain.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure

Ferromagnetic properties of GdN thin films studied by temperature dependent circular polarized spectroscopy

H. Yoshitomi, R. Vidyasagar, S. Kitayama, T. Kita, H. Ohta, S. Okubo, Y. Fukuoka, and T. Sakurai

Appl. Phys. Lett. 101, 072403 (2012); http://dx.doi.org/10.1063/1.4746265 (5 pages) | Cited 2 times

Online Publication Date: 13 August 2012

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Magneto-optical properties of GdN thin films have been investigated by employing temperature dependent optical circular dichroism spectroscopy and angular dependent resonance field measurement. Spin-splitting in the band structure of GdN thin films has been evaluated by optical circular dichroism absorbance spectra, and the manifested spin-splitting energy ascribed to the difference between majority and minority spin band states in GdN. The plot of left circular polarization and right circular polarization bandgap reflects the half-hysteresis loop (positive side) trend, which is evidenced by magnetization measurements. The angular dependent resonance field measurements showed strong magnetic anisotropy along in-plane of GdN, which is attributed to the disturbance in the spin alignment in GdN. We demonstrate that the ferromagnetic properties depend on the film thickness. These results provide a pathway to control the spin ordering using circularly polarized light and the magnetic anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
78.66.Li Other semiconductors
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Mechanism of magnetoresistance ratio enhancement in MgO/NiFe/MgO heterostructure by rapid thermal annealing

Chong-Jun Zhao, Yang Liu, Jing-Yan Zhang, Li Sun, Lei Ding, Peng Zhang, Bao-Yi Wang, Xing-Zhong Cao, and Guang-Hua Yu

Appl. Phys. Lett. 101, 072404 (2012); http://dx.doi.org/10.1063/1.4745916 (5 pages) | Cited 2 times

Online Publication Date: 14 August 2012

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To reveal thermal effects on the film quality/microstructure evolution and the resulted magnetoresistance (MR) ratio in MgO/NiFe/MgO heterostructures, positron annihilation spectroscopy studies have been performed. It is found that the ionic interstitials in the MgO layers recombine with the nearby vacancies at lower annealing temperatures (200-300 °C) and lead to a slow increase in sample MR. Meanwhile, vacancy defects agglomeration/removal and ordering acceleration in MgO will occur at higher annealing temperatures (450-550 °C) and the improved MgO and MgO/NiFe interfaces microstructure are responsible for the observed significant MR enhancement.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.70.Bj Positron annihilation
61.72.jd Vacancies
61.72.jj Interstitials
61.72.Cc Kinetics of defect formation and annealing

High magnetostriction and coupling coefficient for sintered cobalt ferrite derived from superparamagnetic nanoparticles

K. Khaja Mohaideen and P. A. Joy

Appl. Phys. Lett. 101, 072405 (2012); http://dx.doi.org/10.1063/1.4745922 (4 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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High magnetostriction (λ) and coupling coefficient (dλ/dH) of 315 ppm and 1.97×10−9 A−1m, respectively, are obtained at room temperature for sintered cobalt ferrite derived from nanocrystalline powders. Also, the powder was compacted at a low pressure of 8 MPa and sintered for a short duration of 10 min at 1450 °C. Magnetic annealing at 300 °C in a field of 0.5 T for 30 min further enhanced the magnetostriction coefficient to 345 ppm with a higher coupling coefficient 2.12×10−9 A−1m. The magnetic field above which maximum magnetostriction is observed is reduced by almost half after magnetic annealing.
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75.80.+q Magnetomechanical effects, magnetostriction
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
75.20.Ck Nonmetals
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Nt Magnetic annealing and temperature-hysteresis effects

Carriers dependence of the magnetic properties in magnetic topological insulator Sb1.95−xBixCr0.05Te3

H. Li, Y. R. Song, Meng-Yu Yao, Fang Yang, Lin Miao, Fengfeng Zhu, Canhua Liu, C. L. Gao, Dong Qian, X. Yao, Jin-Feng Jia, Y. J. Shi, and D. Wu

Appl. Phys. Lett. 101, 072406 (2012); http://dx.doi.org/10.1063/1.4746404 (4 pages) | Cited 1 time

Online Publication Date: 14 August 2012

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Bulk carrier density and magnetic properties of Sb1.95−xBixCr0.05Te3 single crystals were studied. We found that the carrier density can be tuned by Bi substitution. Both the Curie temperature and magnetic moments are strongly related to the carrier density, which suggests the existence of intrinsic ferromagnetism in Cr-doped Sb2Te3 magnetic topological insulator that is very important for spin-related applications.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Probing a single nuclear spin in a silicon single electron transistor

F. Delgado, R. Aguado, and J. Fernández-Rossier

Appl. Phys. Lett. 101, 072407 (2012); http://dx.doi.org/10.1063/1.4746260 (4 pages)

Online Publication Date: 16 August 2012

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We study single electron transport across a single Bi dopant in a silicon nanotransistor to assess how the strong hyperfine coupling with the Bi nuclear spin I = 9/2 affects the transport characteristics of the device. In the sequential tunneling regime we find that at, temperatures in the range of 100 mK, dI/dV curves reflect the zero field hyperfine splitting as well as its evolution under an applied magnetic field. Our non-equilibrium quantum simulations show that nuclear spins can be partially polarized parallel or antiparallel to the electronic spin just tuning the applied bias.
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85.35.Gv Single electron devices
85.30.De Semiconductor-device characterization, design, and modeling

Fast domain wall dynamics in MnAs/GaAs films

M. Tortarolo, L. Thevenard, H. J. von Bardeleben, M. Cubukcu, V. Etgens, M. Eddrief, and C. Gourdon

Appl. Phys. Lett. 101, 072408 (2012); http://dx.doi.org/10.1063/1.4746381 (4 pages)

Online Publication Date: 16 August 2012

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Field-induced domain wall (DW) dynamics was investigated in MnAs/GaAs(100) films by means of longitudinal Kerr microscopy and a field pulse technique. Saw-tooth type domains were observed in the studied temperature range. DW velocities up to 950 m s−1 were measured at 200 K and up to 540 m s−1 at 290 K, at the beginning of the nucleation of the non-ferromagnetic β phase within the ferromagnetic α phase. Different propagation regimes were observed depending on the magnitude of the Walker field compared to the depinning field, which depends on the progressive nucleation of an unordered β phase. The results are interpreted in the framework of the one-dimensional model (1D) for DW propagation.
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75.60.Ch Domain walls and domain structure
75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
64.60.Q- Nucleation
75.78.Fg Dynamics of domain structures
75.50.Dd Nonmetallic ferromagnetic materials

Spin-torque effect on spin wave modes in magnetic nanowires

Voicu O. Dolocan

Appl. Phys. Lett. 101, 072409 (2012); http://dx.doi.org/10.1063/1.4747152 (4 pages)

Online Publication Date: 17 August 2012

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The interaction between a spin polarized dc electrical current and spin wave modes of a cylindrical nanowire is investigated in this report. We found that close to the critical current, the uniform mode is suppressed, while the edge mode starts to propagate into the sample. When the current exceeds the critical value, this phenomenon is even more accentuated. The edge mode becomes the uniform mode of the nanowire. The higher spin wave modes are slowly pushed away by the current until the propagating mode remains.
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75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.75.-c Magnetic properties of nanostructures
72.25.-b Spin polarized transport

Enhancement of perpendicular magnetic anisotropy thanks to Pt insertions in synthetic antiferromagnets

S. Bandiera, R. C. Sousa, S. Auffret, B. Rodmacq, and B. Dieny

Appl. Phys. Lett. 101, 072410 (2012); http://dx.doi.org/10.1063/1.4745924 (4 pages)

Online Publication Date: 17 August 2012

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Synthetic antiferromagnets are of great interest as reference layers in magnetic tunnel junctions since they allow decreasing the dipolar coupling between the two magnetic electrodes and exhibit larger pinning fields than single reference layers. In this letter, we investigate the effect of the insertion of an ultrathin Pt layer in contact with the Ru spacer in synthetic antiferromagnets with perpendicular magnetic anisotropy. Surprisingly, for Ru thickness below 0.75 nm, the antiferromagnetic coupling amplitude through Ru first increases upon Pt insertion up to a critical Pt thickness (∼0.25 nm) above which coupling decreases. In addition, the corresponding increase of perpendicular magnetic anisotropy enhances the thermal stability of the structure.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics

Optimization of Ta thickness for perpendicular magnetic tunnel junction applications in the MgO-FeCoB-Ta system

Vincent Sokalski, Matthew T. Moneck, En Yang, and Jian-Gang Zhu

Appl. Phys. Lett. 101, 072411 (2012); http://dx.doi.org/10.1063/1.4746426 (4 pages) | Cited 2 times

Online Publication Date: 17 August 2012

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The impact of Ta thickness on magnetic anisotropy and interlayer magnetic coupling is evaluated for the Ta-FeCoB-MgO thin film system commonly used in magnetic tunnel junctions. It is shown that there exists a window of Ta thickness where strong magnetic coupling of FeCoB with another magnetic layer is achievable through Ta while still maintaining properties required for use in a perpendicular magnetic tunnel junction. We also expand on existing knowledge about the role of annealing temperature, film composition, and seedlayer sequence on magnetic anisotropy in Ta/FeCoB/MgO tri-layers of varying FeCoB thickness.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Gh Other heat and thermomechanical treatments
75.30.Gw Magnetic anisotropy

Magnetic reversal in a YFe2 dominated DyFe2/YFe2 multilayer film

G. B. G. Stenning, G. J. Bowden, S. A. Gregory, J.-M. L. Beaujour, P. A. J. de Groot, G. van der Laan, L. R. Shelford, P. Bencok, P. Steadman, A. N. Dobrynin, and T. Hesjedal

Appl. Phys. Lett. 101, 072412 (2012); http://dx.doi.org/10.1063/1.4746749 (4 pages) | Cited 2 times

Online Publication Date: 17 August 2012

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Magnetic reversal in a (110)-oriented [DyFe2(60 Å)/YFe2(240 Å)]×15 multilayer film is investigated using magnetometry, micro-magnetic modeling, and element-specific soft x-ray magnetic circular dichroism. At temperatures between ∼60 and 120 K, the magnetic reversal involves a two-step process. It is shown that the reversal mechanism can be described as switching from an in-plane [001] reversed anti-ferromagnetic state, to an out-of-plane [100] transverse spring exchange state, and finally to an in-plane [00math] magnetic exchange spring state.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.60.Jk Magnetization reversal mechanisms
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