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11 Jun 2012

Volume 100, Issue 24, Articles (24xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 241101 (2012); http://dx.doi.org/10.1063/1.4724309 (3 pages)

Miriam S. Vitiello, Leonardo Viti, Lorenzo Romeo, Daniele Ercolani, G. Scalari, J. Faist, F. Beltram, L. Sorba, and A. Tredicucci
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Room temperature femtotesla radio-frequency atomic magnetometer

W. Chalupczak, R. M. Godun, S. Pustelny, and W. Gawlik

Appl. Phys. Lett. 100, 242401 (2012); http://dx.doi.org/10.1063/1.4729016 (4 pages)

Online Publication Date: 12 June 2012

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A radio-frequency tunable atomic magnetometer with a sensitivity of about 1 fT/Hz1/2 in a range of 10–500 kHz is demonstrated. The magnetometer is operated in the orientation configuration in which atoms are pumped to the stretched atomic state by a scheme based on indirect optical pumping using only one unmodulated, low-power laser. The magnetometer operates with cesium atoms, which have sufficient vapor pressure near room temperature to enable high magnetometric sensitivities. The technique enables a compact and robust module to be constructed that could become an in-the-field device.
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07.55.Ge Magnetometers for magnetic field measurements

Spin dynamics of magnetic nanostructures investigated by micromagnetic simulations

R. Rückriem, P. Krone, T. Schrefl, and M. Albrecht

Appl. Phys. Lett. 100, 242402 (2012); http://dx.doi.org/10.1063/1.4729054 (5 pages)

Online Publication Date: 12 June 2012

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Micromagnetic simulations were performed to investigate the spin dynamics of cylindrical magnetic nanostructures of various sizes down to 20 nm. The presented simulation technique provides information on the equilibrium states, magnetization precession, and spatial distributions of excited spin wave modes of individual nanostructures. Larger cylindrical nanostructures reveal a flower state magnetization configuration and show rather complex edge and center modes, which depend strongly on the saturation magnetization. This behavior allows controlling the precession frequencies, which is important in microwave-assisted three-dimensional magnetic recording, where layers of different resonance frequency need to be addressed and switched individually.
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75.75.Jn Dynamics of magnetic nanoparticles
75.78.Cd Micromagnetic simulations
75.30.Ds Spin waves
75.50.Tt Fine-particle systems; nanocrystalline materials

Large magnetic moment of gadolinium substituted topological insulator: Bi1.98Gd0.02Se3

Y. R. Song, Fang Yang, Meng-Yu Yao, Fengfeng Zhu, Lin Miao, Jin-Peng Xu, Mei-Xiao Wang, H. Li, X. Yao, Fuhao Ji, S. Qiao, Z. Sun, G. B. Zhang, B. Gao, Canhua Liu, et al.

Appl. Phys. Lett. 100, 242403 (2012); http://dx.doi.org/10.1063/1.4729056 (3 pages) | Cited 1 time

Online Publication Date: 12 June 2012

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The crystal structure, electronic, and magnetic properties of Gadolinium (Gd) substituted Bi2Se3—represented by Bi1.98Gd0.02Se3—were investigated systematically by scanning tunneling microscopy, angle-resolved photoemission spectroscopy, and superconducting quantum interference device. Gd dopants with valence of 3+ were mainly found to substitute Bi atoms. Each Gd3+ ion has a magnetic moment as large as ∼6.9μB in the bulk paramagnetic state.
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75.30.Cr Saturation moments and magnetic susceptibilities
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.66.Fn Inorganic compounds
71.20.Ps Other inorganic compounds
75.20.Ck Nonmetals

Ferromagnetism of cobalt-doped anatase TiO2 studied by bulk- and surface-sensitive soft x-ray magnetic circular dichroism

V. R. Singh, K. Ishigami, V. K. Verma, G. Shibata, Y. Yamazaki, T. Kataoka, A. Fujimori, F.-H. Chang, D.-J. Huang, H.-J. Lin, C. T. Chen, Y. Yamada, T. Fukumura, and M. Kawasaki

Appl. Phys. Lett. 100, 242404 (2012); http://dx.doi.org/10.1063/1.4729123 (5 pages) | Cited 2 times

Online Publication Date: 12 June 2012

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We have studied magnetism in anatase Ti1−xCoxO2−δ (x = 0.05) thin films with various electron carrier densities, by soft x-ray magnetic circular dichroism (XMCD) measurements at the Co L2,3 absorption edges. For electrically conducting samples, the magnetic moment estimated by XMCD was <0.3 μB/Co using the surface-sensitive total electron yield mode, while it was 0.3–2.4 μB/Co using the bulk-sensitive total fluorescence yield mode. The latter value is in the same range as the saturation magnetization 0.6–2.1 μB/Co deduced by SQUID measurement. The magnetization and the XMCD intensity increased with carrier density, consistent with the carrier-induced origin of the ferromagnetism.
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75.70.Ak Magnetic properties of monolayers and thin films
73.61.Le Other inorganic semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic anisotropy engineering: Single-crystalline Fe films on ion eroded ripple surfaces

M. O. Liedke, M. Körner, K. Lenz, F. Grossmann, S. Facsko, and J. Fassbender

Appl. Phys. Lett. 100, 242405 (2012); http://dx.doi.org/10.1063/1.4729151 (4 pages)

Online Publication Date: 12 June 2012

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We present a method to preselect the direction of an induced in-plane uniaxial magnetic anisotropy (UMA) in thin single-crystalline Fe films on MgO(001). Ion beam irradiation is used to modulate the MgO(001) surface with periodic ripples on the nanoscale. The ripple direction determines the orientation of the UMA, whereas the intrinsic cubic anisotropy of the Fe film is not affected. Thus, it is possible to superimpose an in-plane UMA with a precision of a few degrees—a level of control not reported so far that can be relevant for example in spintronics.
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75.70.Ak Magnetic properties of monolayers and thin films
61.80.Jh Ion radiation effects
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys

Tunable misalignment of ferromagnetic and antiferromagnetic easy axes in exchange biased bilayers

R. L. Rodríguez-Suárez, L. H. Vilela-Leão, T. Bueno, J. B. S. Mendes, P. Landeros, S. M. Rezende, and A. Azevedo

Appl. Phys. Lett. 100, 242406 (2012); http://dx.doi.org/10.1063/1.4729040 (4 pages)

Online Publication Date: 13 June 2012

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In this paper we report experiments that show how to tune the unidirectional anisotropy field in exchange biased Ni81Fe19/Ir20Mn80 bilayers grown by sputtering. During growth the samples are held in an obliquely inclined stage, and simultaneously a static magnetic field is applied along an arbitrary direction in the film plane. While the direction of the ferromagnetic anisotropy field is given by the tilted columnar microstructures induced by the oblique sputtering, the direction of the unidirectional field can be tuned by the application of the in situ magnetic field. The magnetic properties were investigated using the ferromagnetic resonance technique.
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68.55.A- Nucleation and growth
73.40.Gk Tunneling
75.30.Gw Magnetic anisotropy
75.50.Bb Fe and its alloys
81.15.Cd Deposition by sputtering

On the Curie temperature dependency of the magnetocaloric effect

J. H. Belo, J. S. Amaral, A. M. Pereira, V. S. Amaral, and J. P. Araújo

Appl. Phys. Lett. 100, 242407 (2012); http://dx.doi.org/10.1063/1.4726110 (4 pages) | Cited 5 times

Online Publication Date: 13 June 2012

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We investigate the magnetocaloric effect dependency on the most important microscopic parameters of ferromagnetic materials, such as the Curie temperature (TC), the spin value (J), and the magnetic field change (ΔH). Second- and first-order phase transition systems are considered, using the Bean-Rodbell model [C. P. Bean and D. S. Rodbell, Phys. Rev. 126, 104 (1962)] of magnetovolume interactions on the Weiss mean-field model [P. Weiss, J. Phys. Theory Appl. 6, 661 (1907)]. The magnetocaloric effect simulations show a surprising TC−2/3 linear dependence of the maximum entropy change (ΔSmmax), which is observed for all simulated systems. An approximate state equation establishing the dependence of ΔSmmax on TC, ΔH, J, and the magnetic atoms density (N) is presented. The dependence of maximum magnetic entropy change on TC−2/3 is validated by a wide set of experimental results of second- and first-order phase transition materials that are promising for magnetic refrigeration applications at room temperature.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.80.+q Magnetomechanical effects, magnetostriction
65.40.gd Entropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Normal or inverse magnetocaloric effects at the transition between antiferromagnetism and ferromagnetism

Bing Li (李昺), Wen Liang (梁文), Weijun Ren (任卫军), Weijin Hu (胡卫进), Ji Li (李季), Changqing Jin (靳常青), and Zhidong Zhang (张志东)

Appl. Phys. Lett. 100, 242408 (2012); http://dx.doi.org/10.1063/1.4729122 (4 pages) | Cited 2 times

Online Publication Date: 13 June 2012

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The magnetocaloric effect (MCE) at the antiferromagnetic (AF) to ferromagnetic (F) phase transition in Mn1.05Ni0.85Ge and CrO1.86F0.14, and the MCE at the F-AF transition in Tb3Co have been investigated. Mn1.05Ni0.85Ge and CrO1.86F0.14 are found to exhibit the inverse MCE whereas the MCE of Tb3Co is normal. For these compounds, the dependence of the transition temperature on the applied magnetic field B has been studied. A thermodynamical analysis is presented of the sign of the magnetic-entropy change in these three compounds which are representatives of two different types of B-T diagrams. Other possible B-T diagrams are discussed and the analysis is extended to AF-F and F-AF phase transitions reported in literature.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
65.40.gd Entropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Domain wall configuration and magneto-transport properties in dual spin-valve with nanoconstriction

Byong Sun Chun, Han-Chun Wu, Su Jung Noh, In Chang Chu, Santiago Serrano-Guisan, Chanyong Hwang, Igor V. Shvets, Zhi-Min Liao, Mohamed Abid, and Young Keun Kim

Appl. Phys. Lett. 100, 242409 (2012); http://dx.doi.org/10.1063/1.4729126 (5 pages) | Cited 1 time

Online Publication Date: 13 June 2012

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We investigated the effect of external field on magneto-transport properties of synthetic antiferromagnet dual spin-valve with nanoconstriction with focus on domain wall (DW) configuration and magnetization reversal process. As magnetic field rotated from in-plane to out-of-plane along hard axis configuration, the magnetization reversal mode changed from a vortex to a transverse type, and a multistep switching process appeared due to the development of a transverse magnetization reversal mode with DW pushing towards the higher anisotropy region. The difference in the shape of nanoconstriction made an asymmetric energy barrier to the DW propagation which resulted in an asymmetry depinning field.
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75.60.Ch Domain walls and domain structure
75.60.Jk Magnetization reversal mechanisms
61.46.-w Structure of nanoscale materials
75.50.Ee Antiferromagnetics
75.50.Kj Amorphous and quasicrystalline magnetic materials

Exchange bias effects in epitaxial Fe3O4/BiFeO3 heterostructures

T. L. Qu, Y. G. Zhao, P. Yu, H. C. Zhao, S. Zhang, and L. F. Yang

Appl. Phys. Lett. 100, 242410 (2012); http://dx.doi.org/10.1063/1.4729408 (4 pages) | Cited 5 times

Online Publication Date: 13 June 2012

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High quality Fe3O4 (5–20 nm)/BiFeO3 (BFO) heterostructures have been grown by pulsed laser deposition on (001) SrTiO3 (STO) substrates. Large exchange bias (EB) effects have been observed below 200 K in Fe3O4/BFO/STO structures compared with Fe3O4/STO structures. The exchange bias field decreases when increasing temperature or the thickness of Fe3O4 layer, and does not change after annealing in 0.1 T field from 700 K to room temperature across Neel temperature of BFO. A possible mechanism was proposed based on the interface spin coupling between Fe3O4 and BFO. Our work shed new light on the study of exchange bias effect in BFO system as well as the application for magnetoelectric devices.
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71.70.Gm Exchange interactions
75.30.Ds Spin waves
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.07.Bc Nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition

Magnetization dynamics and reversal mechanism of Fe filled Ni80Fe20 antidot nanostructures

X. M. Liu, J. Ding, and A. O. Adeyeye

Appl. Phys. Lett. 100, 242411 (2012); http://dx.doi.org/10.1063/1.4729428 (5 pages)

Online Publication Date: 13 June 2012

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We investigate the magnetization dynamics and reversal mechanism of Fe filled Ni80Fe20 antidot nanostructures. The mutual magnetostatic coupling between the two ferromagnetic nanostructures leads to a significant modification to the magnetization reversal mechanism and ferromagnetic resonance mode profiles when compared with reference Fe dots and Ni80Fe20 antidot array. Our experimental results are in qualitative agreement with both the static and dynamic micromagnetic simulations.
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75.75.Jn Dynamics of magnetic nanoparticles
75.78.Cd Micromagnetic simulations
75.60.Jk Magnetization reversal mechanisms
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Ferromagnetic GeMn thin film prepared by ion implantation and ion beam induced epitaxial crystallization annealing

C. H. Chen, H. Niu, D. C. Yan, H. H. Hsieh, C. P. Lee, and C. C. Chi

Appl. Phys. Lett. 100, 242412 (2012); http://dx.doi.org/10.1063/1.4729752 (4 pages)

Online Publication Date: 15 June 2012

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Ferromagnetic GeMn was prepared by Mn implantation followed by ion beam-induced epitaxial crystallization annealing. The damage caused by Mn implantation was repaired by subsequent helium ion irradiation. Various structural analyses were performed and Mn ions were found to incorporate uniformly into the Ge lattice without the formation of any secondary phases. The remnant magnetic moment exhibited room temperature ferromagnetism. Anomalous Hall effect and field dependent magnetization were measured at the same time at room temperature indicating spin polarized free carrier transport. Additional measurement using x-ray magnetic circular dichroism also revealed that the carriers were spin-polarized.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.-b Spin polarized transport
73.61.Cw Elemental semiconductors

Origin of magnetic anisotropy and spiral spin order in multiferroic BiFeO3

J. T. Zhang, X. M. Lu, J. Zhou, H. Sun, J. Su, C. C. Ju, F. Z. Huang, and J. S. Zhu

Appl. Phys. Lett. 100, 242413 (2012); http://dx.doi.org/10.1063/1.4729555 (4 pages) | Cited 1 time

Online Publication Date: 15 June 2012

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The first-principles calculations and thermodynamic modeling are combined to investigate the magnetic properties of BiFeO3. Our calculations indicate that the single-ion anisotropy and the anisotropic superexchange coupling contribute the same magnitude to the easy-magnetization-plane anisotropy. We show that the competition between the isotropic superexchange and the Dzyaloshinskii-Moriya interaction [I. Dzyaloshinsky, J. Phys. Chem. Solids 4, 241 (1958) and T. Moriya, Phys. Rev. 120, 91 (1960)] of the nearest-neighbor Fe spins provides the microscopic mechanism for the origin of the long period spiral spin order, and the induced spontaneous magnetization exhibits a sinusoidal arrangement under the spiral order.
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75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves
75.78.-n Magnetization dynamics
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions
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