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23 May 2011

Volume 98, Issue 21, Articles (21xxxx)

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Appl. Phys. Lett. 98, 212504 (2011); http://dx.doi.org/10.1063/1.3593371 (3 pages)

K. Okumura, T. Ishikura, M. Soda, T. Asaka, H. Nakamura, Y. Wakabayashi, and T. Kimura
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Significant ferrimagnetism observed in Aurivillius Bi4Ti3O12 doped by antiferromagnetic LaFeO3

Fei-Xiang Wu, Zhong Chen, Y. B. Chen, Shan-Tao Zhang, Jian Zhou, Yong-Yuan Zhu, and Yan-Feng Chen

Appl. Phys. Lett. 98, 212501 (2011); http://dx.doi.org/10.1063/1.3592737 (3 pages) | Cited 4 times

Online Publication Date: 23 May 2011

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Highly crystalline quality c-axis epitaxial nLaFeO3–Bi4Ti3O12 (n = 0.5,1.0,1.5) thin films were deposited on SrTiO3 (001) substrates by pulsed laser deposition. The x-ray diffraction and transmission electron microscopy characterizations confirm that there are designed even-odd number perovskite-block structures in n = 0.5 and 1.5 films while it has even-even number ones in n = 1.0 films. The remarkable physical property of n = 0.5 and 1.5 samples is the presence of ferrimagnetism even up to room temperature. While it is antiferromagentic property in n = 1.0 sample. The observed ferrimagentism is explained qualitatively by considering the crystal structure in nLaFeO3–Bi4Ti3O12.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.aj Insulators
81.15.Fg Pulsed laser ablation deposition
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics
61.72.up Other materials

Planar millimeter wave band-stop filters based on the excitation of confined magnetostatic waves in barium hexagonal ferrite thin film strips

Lei Lu, Young-Yeal Song, Joshua Bevivino, and Mingzhong Wu

Appl. Phys. Lett. 98, 212502 (2011); http://dx.doi.org/10.1063/1.3592817 (3 pages) | Cited 1 time

Online Publication Date: 23 May 2011

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A planar millimeter wave band-stop filter based on confined magnetostatic wave (MSW) excitations in an M-type barium hexagonal ferrite (BaM) film strip was demonstrated. The device consists of a BaM film strip on the top of a coplanar waveguide with the strip length along the signal line. For zero magnetic fields, the device shows a band-stop filtering response at 53 GHz. This response originates from the excitation of confined MSW modes across the BaM strip width. The filter operation frequency is tunable with low fields. This tuning relies on the change in the MSW dispersion with field.
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84.30.Vn Filters
84.40.Az Waveguides, transmission lines, striplines
84.40.Dc Microwave circuits

Giant anisotropic magnetoresistance in bilayered La1.2Sr1.8Mn2O7 single crystals

Wei Ning, Zhe Qu, You-Ming Zou, Lang-Sheng Ling, Lei Zhang, Chuan-Ying Xi, Hai-Feng Du, Run-Wei Li, and Yu-Heng Zhang

Appl. Phys. Lett. 98, 212503 (2011); http://dx.doi.org/10.1063/1.3593486 (3 pages) | Cited 3 times

Online Publication Date: 23 May 2011

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We report an observation of anomalous anisotropic magnetoresistance (AMR) in bilayered La1.2Sr1.8Mn2O7 single crystals. A giant AMR is found to be 80% under a magnetic field of 1 T near the metal-insulator transition temperature, where AMR is defined as AMR = [ρ(H⊥c)−ρ(H∥c)]/ρ(H⊥c)×100%, and ρ(H⊥c) and ρ(H∥c) are the resistivity with the magnetic field perpendicular and parallel to c-axis, respectively. The AMR effect shows strong temperature and magnetic field dependences, and indicates a close interrelation with the anisotropic field-tuned metal-insulator transition.
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75.47.De Giant magnetoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
71.30.+h Metal-insulator transitions and other electronic transitions

Magnetism and magnetoelectricity of a U-type hexaferrite Sr4Co2Fe36O60

K. Okumura, T. Ishikura, M. Soda, T. Asaka, H. Nakamura, Y. Wakabayashi, and T. Kimura

Appl. Phys. Lett. 98, 212504 (2011); http://dx.doi.org/10.1063/1.3593371 (3 pages) | Cited 7 times

Online Publication Date: 23 May 2011

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We report on structural, magnetic, and magnetoelectric (ME) properties of a U-type hexaferrite Sr4Co2Fe36O60 prepared by solid state reaction. Samples sintered at 1150–1180 °C in oxygen contain the fewest impurity phases and show highly insulating behavior. Powder neutron diffraction results reveal that a commensurate magnetic order with a (0,0,3/2) propagation vector develops below TN2 ∼ 350 K. Corresponding to the appearance of the magnetic order, the sample shows a small ME effect. These results suggest that Sr4Co2Fe36O60 is a room-temperature ME material in which the origin of the ME effect is similar to those of other ME hexaferrites.
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75.85.+t Magnetoelectric effects, multiferroics
61.66.Fn Inorganic compounds
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Coercivity change in an FePt thin layer in a Hall device by voltage application

Takeshi Seki, Makoto Kohda, Junsaku Nitta, and Koki Takanashi

Appl. Phys. Lett. 98, 212505 (2011); http://dx.doi.org/10.1063/1.3595318 (3 pages) | Cited 10 times

Online Publication Date: 24 May 2011

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The coercivity (Hc) of a perpendicularly magnetized FePt layer was modulated by applying the voltage (Vapp) to a Hall device through MgO and Al–O insulating layers. A change in ∼ 40 Oe in Hc was observed by changing Vapp from −13 to 13 V. From the quantitative analysis of the voltage effect on Hc, the change in the anisotropy energy by voltage application was evaluated to be 18.6 fJ/V m, which was of the same order as the theoretical prediction. The role of the MgO layer for the voltage effect was also discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
85.75.Nn Hybrid Hall devices
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

X-ray reflectance studies of interface in ion beam sputtered CoFeB/MgO bilayers

M. Raju, Sujeet Chaudhary, and D. K. Pandya

Appl. Phys. Lett. 98, 212506 (2011); http://dx.doi.org/10.1063/1.3595417 (3 pages) | Cited 4 times

Online Publication Date: 25 May 2011

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This letter reports specular and diffuse x-ray reflectance studies of the interface in the ion beam sputtered CoFeB( ∼ 5–8 nm)/MgO( ∼ 2–5 nm) bilayers. The study reveals the specific roles of oxygen ion energy, substrate temperature, and reactive gas ambient on controlling the interface width in the bilayers. Depending on oxidation-method employed for MgO growth the interface width varies between 0.51 and 0.20 nm. Energy of assist ions ( ≤ 50 eV) plays a key role compared to the growth temperature in determining the sharpness of the interface. The bottom grown CoFeB exhibited significant increase in coercivity (HC), which also depends on MgO-growth process.
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81.15.Cd Deposition by sputtering
81.15.Jj Ion and electron beam-assisted deposition; ion plating
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Direct measurement of the spin diffusion length by Andreev spectroscopy

A. Geresdi, A. Halbritter, F. Tanczikó, and G. Mihály

Appl. Phys. Lett. 98, 212507 (2011); http://dx.doi.org/10.1063/1.3593959 (3 pages) | Cited 1 time

Online Publication Date: 25 May 2011

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The application of point contact Andreev spectroscopy for the measurement of the spin diffusion length is demonstrated by studying the spin relaxation in platinum thin films grown on the top of a ferromagnetic cobalt layer. Using this local probe technique, the temperature dependence of the spin diffusion length was determined, and various sources of the spin relaxation in platinum were identified. At low temperatures the spin lifetime is found to be three orders of magnitude larger than the momentum lifetime. The applied method is selectively sensitive to spin-flip processes even in the presence of a huge background of momentum scattering.
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72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Ds Spin waves
68.55.aj Insulators

Element-specific study of epitaxial NiO/Ag/CoO/Fe films grown on vicinal Ag(001) using photoemission electron microscopy

Y. Meng, J. Li, A. Tan, E. Jin, J. Son, J. S. Park, A. Doran, A. T. Young, A. Scholl, E. Arenholz, J. Wu, C. Hwang, H. W. Zhao, and Z. Q. Qiu

Appl. Phys. Lett. 98, 212508 (2011); http://dx.doi.org/10.1063/1.3595274 (3 pages)

Online Publication Date: 26 May 2011

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NiO/Ag/CoO/Fe single crystalline films are grown epitaxially on a vicinal Ag(001) substrate using molecular beam epitaxy and investigated by photoemission electron microscopy. We find that after zero-field cooling, the in-plane Fe magnetization switches from parallel to perpendicular direction of the atomic steps of the vicinal surface at thinner CoO thickness but remains in its original direction parallel to the steps at thicker CoO thickness. CoO and NiO domain imaging result shows that both CoO/Fe and NiO/CoO spins are perpendicularly coupled, suggesting that the Fe magnetization switching may be associated with the rotatable-frozen spin transition of the CoO film.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced ferromagnetism in grain boundary of Co-doped ZnO films: A magnetic force microscopy study

M. N. Lin, H. S. Hsu, J. Y. Lai, M. C. Guo, C. Y. Lin, G. Y. Li, F. Y. Chen, J. J. Huang, S. F. Chen, C. P. Liu, and J. C. A. Huang

Appl. Phys. Lett. 98, 212509 (2011); http://dx.doi.org/10.1063/1.3593384 (3 pages) | Cited 6 times

Online Publication Date: 26 May 2011

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Microscopic grain structures and magnetic properties of Co-doped ZnO-patterned films were studied by combinatorial atomic force microscopy and magnetic force microscopy (MFM) imaging. Whereas Co-doped ZnO was not uniformly magnetized, Co ions were homogeneously doped in the films and substitute from the Zn sites. Most Co:ZnO grains were weakly ferromagnetic (FM) and surrounded by strong FM foamlike grain boundaries networks. No MFM contrast was observed in pure ZnO films grown under similar conditions. The findings clearly demonstrate that defective grain boundaries and magnetic doping have key roles FM properties of diluted magnetic oxides.
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61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films

Disentangling the Mn moments on different sublattices in the half-metallic ferrimagnet Mn3−xCoxGa

P. Klaer, C. A. Jenkins, V. Alijani, J. Winterlik, B. Balke, C. Felser, and H. J. Elmers

Appl. Phys. Lett. 98, 212510 (2011); http://dx.doi.org/10.1063/1.3592802 (3 pages) | Cited 7 times

Online Publication Date: 27 May 2011

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Ferrimagnetic Mn3−xCoxGa compounds have been investigated by magnetic circular dichroism in x-ray absorption (XMCD). Compounds with x>0.5 crystallize in the CuHg2Ti structure. A tetragonal distortion of the cubic structure occurs for x ≤ 0.5. For the cubic phase, magnetometry reveals a linearly increasing magnetization of 2x Bohr magnetons per formula unit obeying the generalized Slater–Pauling rule. XMCD confirms the ferrimagnetic character with Mn atoms occupying two different sublattices with antiparallel spin orientation and different degrees of spin localization and identifies the region 0.6<x ≤ 0.8 as most promising for a high spin polarization at the Fermi level. Individual Mn moments on inequivalent sites are compared to theoretical predictions.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
75.50.Gg Ferrimagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.70.Dm X-ray absorption spectra
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