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7 Sep 2009

Volume 95, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 95, 083506 (2009); http://dx.doi.org/10.1063/1.3216851 (3 pages)

J. Z. Sun, M. C. Gaidis, E. J. O’Sullivan, E. A. Joseph, G. Hu, D. W. Abraham, J. J. Nowak, P. L. Trouilloud, Yu Lu, S. L. Brown, D. C. Worledge, and W. J. Gallagher

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The origins of ferromagnetism in Co-doped ZnO single crystalline films: From bound magnetic polaron to free carrier-mediated exchange interaction

Z. L. Lu, H. S. Hsu, Y. H. Tzeng, F. M. Zhang, Y. W. Du, and J. C. A. Huang

Appl. Phys. Lett. 95, 102501 (2009); http://dx.doi.org/10.1063/1.3224911 (3 pages) | Cited 17 times

Online Publication Date: 8 September 2009

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High-quality Co-doped ZnO single crystalline films with a wide range of carrier concentration and good reproducibility have been grown by molecular beam epitaxy. After the systematic studies of the magnetic and transport properties of the films, we suggest that there are two distinct ferromagnetic mechanisms in different conductivity regimes. In the insulating regime, carriers tend to be localized, favoring the formation of bound magnetic polarons, which leads to ferromagnetism. In the metallic regime, however, most carriers are weakly localized and the free carrier-mediated exchange is dominant. Our experimental observations are well consistent with the recent theoretical description of magnetism in Co-doped ZnO and helpful for understanding the ferromagnetic mechanism in oxide-based diluted magnetic semiconductors.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.30.Et Exchange and superexchange interactions
71.38.-k Polarons and electron-phonon interactions
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials

Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001)

Numan Akdoğan, Bulat Rameev, Sümeyra Güler, Osman Öztürk, Bekir Aktaş, Hartmut Zabel, Rustam Khaibullin, and Lenar Tagirov

Appl. Phys. Lett. 95, 102502 (2009); http://dx.doi.org/10.1063/1.3223583 (3 pages) | Cited 5 times

Online Publication Date: 8 September 2009

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Magnetic anisotropies of Co-implanted ZnO (0001) films grown on single-crystalline Al2O3 (11math0) substrates have been studied by ferromagnetic resonance (FMR) technique for different cobalt implantation doses. The FMR data show that the easy and hard axes have a periodicity of 60° in the film plane, in agreement with the hexagonal structure of the ZnO films. This six-fold in-plane magnetic anisotropy, which is observed for the first time in ZnO-based diluted magnetic semiconductors, is attributed to the substitution of cobalt on Zn sites in the ZnO structure, and a clear indication for long range ferromagnetic ordering between substitutional cobalt ions in the single-crystalline ZnO films.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
68.55.ag Semiconductors
81.05.Dz II-VI semiconductors
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uj III-V and II-VI semiconductors

Highly luminescent garnets for magneto-optical photonic crystals

A. M. Grishin and S. I. Khartsev

Appl. Phys. Lett. 95, 102503 (2009); http://dx.doi.org/10.1063/1.3224204 (3 pages) | Cited 3 times

Online Publication Date: 8 September 2009

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We compare luminescent properties of several Er-doped garnets as building blocks in all-garnet heteroepitaxial magneto-optical photonic crystals. Pulsed laser deposited La3Ga5O12, Gd3Ga5O12, Y3Fe5O12, and rf-magnetron sputtered Bi3Fe5O12 were chosen to host Er3+ ions on dodecahedral lattice sites. Er substituents with the concentration of 0.5 at. % (0.1 garnet formula units) do not decrease giant Faraday rotation in Bi2.9Er0.1Fe5O12 garnet; meanwhile providing intense room temperature C-band photoluminescence (PL). Fe3+ ion works as a sensitizer for Er resulting in fivefold PL enhancement in iron garnets compared to gallium ones. PL lifetime in gallium garnets is in millisecond range reaching almost 6 ms in Gd2.9Er0.1Ga5O12. We conclude Er substitution in gallium and iron garnet layers used both as Bragg mirrors and microcavities promises magneto-optical photonic crystals to become an active lasing medium.
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78.66.Nk Insulators
78.55.Hx Other solid inorganic materials
78.20.Ls Magneto-optical effects
42.70.Qs Photonic bandgap materials
42.79.Bh Lenses, prisms and mirrors
42.79.Dj Gratings

Quantifying interlayer exchange coupling via layer-resolved hysteresis loops in antiferromagnetically coupled manganite/nickelate superlattices

Jihwey Park, Dong Ryeol Lee, Yongseong Choi, John W. Freeland, Ki Bong Lee, Sunil K. Sihna, K. R. Nikolaev, and Allen M. Goldman

Appl. Phys. Lett. 95, 102504 (2009); http://dx.doi.org/10.1063/1.3222944 (3 pages) | Cited 2 times

Online Publication Date: 9 September 2009

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In superlattices made of a half metallic ferromagnet La2/3Ba1/3MnO3(LBMO) and a metallic paramagnet LaNiO3(LNO), the field dependence of the LBMO magnetization was studied using depth- and element-sensitive x-ray resonant magnetic scattering measurements. The superlattices have ten bilayers of LBMO and LNO, and the LBMO layers were antiferromagnetically coupled across LNO spacer layers. From the x-ray measurements, the magnetic hysteresis loop of each LBMO layer was obtained, and subsequently the obtained layer-resolved LBMO hysteresis loops were utilized to determine the interlayer exchange coupling.
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75.30.Et Exchange and superexchange interactions
75.20.Ck Nonmetals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Microwave resonance in Fe/SiO2 nanocomposite

Ji Ma, Jiangong Li, Xia Ni, Xudong Zhang, and Juanjuan Huang

Appl. Phys. Lett. 95, 102505 (2009); http://dx.doi.org/10.1063/1.3224883 (3 pages) | Cited 14 times

Online Publication Date: 10 September 2009

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A broad resonance band in the 1–16 GHz range observed in Fe/SiO2 nanocomposite results from the coexsistence of natural resonance and exchange resonance. The natural resonance appears at 5.91 GHz and can be related to the core spins in the Fe nanoparticles, whereas the exchange resonance appears at 11.01 GHz and can be associated with the surface spins of the Fe nanoparticles in the Fe/SiO2 nanocomposite. Both resonance frequencies depend on the surface anisotropy of the Fe nanoparticles, which can be affected by the Fe particle size, and can be tuned by adjusting the Fe particle size.
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78.70.Gq Microwave and radio-frequency interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions

Defect-mediated room temperature ferromagnetism in vanadium dioxide thin films

Tsung-Han Yang, Sudhakar Nori, Honghui Zhou, and Jagdish Narayan

Appl. Phys. Lett. 95, 102506 (2009); http://dx.doi.org/10.1063/1.3224202 (3 pages) | Cited 12 times

Online Publication Date: 10 September 2009

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High quality epitaxial undoped vanadium oxide (VO2) thin films on c-plane sapphire (0001) substrate have been grown using pulsed laser deposition technique. The as-grown films exhibited excellent structural and transport properties without requiring further annealing treatments for these oxygen-deficient oxide films. The epitaxial growth has been achieved via domain matching epitaxy, where matching of integral multiples of planes occurs across the film-substrate interface. The magnetic properties of vanadium oxide (VO2) films investigated at different temperatures in the range of 10–360 K showed significant magnetic hysteresis as well as saturation of the magnetic moment. The origin of ferromagnetic properties with an estimated Curie temperature above 500 K is discussed in the absence of magnetic impurities in VO2 thin films as determined by x-ray photoelectron spectroscopy, x-ray diffraction, and transmission electron microscopy.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
79.60.Dp Adsorbed layers and thin films
75.30.Hx Magnetic impurity interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities

Experimental modeling of intergranular exchange coupling for perpendicular thin film media

Vincent Sokalski, David E. Laughlin, and Jian-Gang Zhu

Appl. Phys. Lett. 95, 102507 (2009); http://dx.doi.org/10.1063/1.3226638 (3 pages) | Cited 6 times

Online Publication Date: 11 September 2009

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We present an experimental model system that enables quantitative assessment of intergranular exchange coupling in CoCrPt-oxide perpendicular magnetic recording media. A thin film structure consisting of a high coercivity CoPt unicrystal layer and a lower coercivity CoPt layer separated by a thin oxide interlayer is used to model perpendicularly magnetized grains separated by oxide grain boundaries. Exchange coupling energy between the CoPt layers was obtained for SiOx, TiOx, and CrOx interlayers by measuring field shifts from the lower coercivity layer. Cr segregation in CoCrPt grains to grain boundaries is also modeled experimentally and found to significantly suppress exchange coupling.
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75.30.Et Exchange and superexchange interactions
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ss Magnetic recording materials
75.50.Vv High coercivity materials
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