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1 Jan 2007

Volume 90, Issue 1, Articles (01xxxx)

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Appl. Phys. Lett. 90, 012105 (2007); http://dx.doi.org/10.1063/1.2428402 (3 pages)

Jan Bauer, Frank Fleischer, Otwin Breitenstein, Luise Schubert, Peter Werner, Ulrich Gösele, and Margit Zacharias
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Electrical field control magnetic phase transition in nanostructured MnxGe1−x

Jingjing Chen, Kang L. Wang, and Kosmas Galatsis

Appl. Phys. Lett. 90, 012501 (2007); http://dx.doi.org/10.1063/1.2424658 (3 pages) | Cited 26 times

Online Publication Date: 2 January 2007

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The authors have investigated the magnetic, electrical, and structural properties of MnxGe1−x (on Ge substrate) nanostructured films produced by a nanopattern assisted Mn implantation followed by annealing. The semiconducting property and hole-mediated ferromagnetism mechanism enabled them to control the magnetic phase transition in the diluted magnetic semiconductor channel by a gate bias.
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75.50.Pp Magnetic semiconductors
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
75.50.Tt Fine-particle systems; nanocrystalline materials
61.72.Cc Kinetics of defect formation and annealing

Growth and multiferroic properties of hexagonal HoMnO3 films

J.-W. Kim, L. Schultz, K. Dörr, B. B. Van Aken, and M. Fiebig

Appl. Phys. Lett. 90, 012502 (2007); http://dx.doi.org/10.1063/1.2425027 (3 pages) | Cited 16 times

Online Publication Date: 2 January 2007

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Hexagonal, twin-free HoMnO3 (0001) films of 25–240 nm thickness were grown epitaxially on Y2O3:ZrO2(111) substrates using pulsed laser deposition. Ferroelectric polar order and Mn3+ antiferromagnetism were observed by optical second harmonic generation. Magnetization data reveal Ho3+ ordering which is, with subtle deviations, similar to that of bulk crystals. However, three phase transitions below 6 K and thermal hysteresis of magnetization at T<42 K were detected.
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81.15.Fg Pulsed laser ablation deposition
75.70.Ak Magnetic properties of monolayers and thin films
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.80.+q Magnetomechanical effects, magnetostriction

Exchange bias tuned by cooling field in phase separated Y0.2Ca0.8MnO3

T. Qian, G. Li, T. Zhang, T. F. Zhou, X. Q. Xiang, X. W. Kang, and X. G. Li

Appl. Phys. Lett. 90, 012503 (2007); http://dx.doi.org/10.1063/1.2426887 (3 pages) | Cited 42 times

Online Publication Date: 2 January 2007

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The effect of cooling field HFC on the exchange bias field HEB in a spontaneous lamellar ferromagnetic/antiferromagnetic phase separated Y0.2Ca0.8MnO3 has been studied. It is found that with increasing HFC from 1 to 6 T the value of HEB decreases by 37% at 2 K and is inversely proportional to the ferromagnetic layer thickness tFM. This suggests that the tuning of HEB by HFC in Y0.2Ca0.8MnO3 arises from the variation of tFM with HFC. This phenomenon is essentially different from other types of magnetic tunings.
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75.30.Et Exchange and superexchange interactions
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics

Awaking of ferromagnetism in GaMnN through control of Mn valence

S. Sonoda, I. Tanaka, F. Oba, H. Ikeno, H. Hayashi, T. Yamamoto, Y. Yuba, Y. Akasaka, K. Yoshida, M. Aoki, M. Asari, T. Araki, Y. Nanishi, K. Kindo, and H. Hori

Appl. Phys. Lett. 90, 012504 (2007); http://dx.doi.org/10.1063/1.2408646 (3 pages) | Cited 8 times

Online Publication Date: 2 January 2007

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Room temperature ferromagnetism of GaMnN thin film is awaked by a mild hydrogenation treatment of a sample synthesized by molecular beam epitaxy. Local environment of Mn atoms is monitored by Mn-L2,3 near edge x-ray absorption fine structure technique. Doped Mn ions are present at substitutional sites of Ga both before and after the hydrogenation. No secondary phase can be detected. Major valency of Mn changes from 3+ to 2+ by the hydrogenation. The present result supports the model that the ferromagnetism occurs when Mn2+ and Mn3+ are coexistent and holes in the midgap Mn band mediate the magnetic coupling.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.70.Dm X-ray absorption spectra
78.66.Fd III-V semiconductors

Effect of Ta getter on the quality of MgO tunnel barrier in the polycrystalline CoFeB/MgO/CoFeB magnetic tunnel junction

Y. S. Choi, Y. Nagamine, K. Tsunekawa, H. Maehara, D. D. Djayaprawira, S. Yuasa, and K. Ando

Appl. Phys. Lett. 90, 012505 (2007); http://dx.doi.org/10.1063/1.2426902 (3 pages) | Cited 18 times

Online Publication Date: 2 January 2007

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X-ray photoelectron spectroscopy and high-resolution Rutherford backscattering reveal that Ta getter presputtering enhances the stoichiometry and lowers the interstitial defect density of MgO barrier. This results in higher magnetoresistance ratio, 205%, of magnetic tunnel junction, compared to 46% for no Ta getter, at 1.2 nm MgO thickness. Fitting yields the corresponding barrier height of the MgO of 3.0 eV, which is higher compared to 2.3 eV for without Ta getter. However, the tunnel junction prepared with Ta getter shows lower resistance-area product by an order of magnitude. Microstructure of MgO barrier and oxidation of bottom electrode can be attributed to the contradictory results.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys
75.50.Bb Fe and its alloys
61.72.J- Point defects and defect clusters
61.72.Yx Interaction between different crystal defects; gettering effect
61.66.Bi Elemental solids
61.66.Dk Alloys

aMagnetic control of spin reorientation and magnetodielectric effect below the spin compensation temperature in TmFeO3

R. Muralidharan, T.-H. Jang, C.-H. Yang, Y. H. Jeong, and T. Y. Koo

Appl. Phys. Lett. 90, 012506 (2007); http://dx.doi.org/10.1063/1.2426928 (3 pages) | Cited 8 times

Online Publication Date: 3 January 2007

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The onset of antiferromagnetic transition, spin reorientation, and spin compensation of TmFeO3 single crystals were investigated by the magnetic and heat capacity measurements. Control of spin reorientation by magnetic field and anomalous hysteretic behavior in domain switching were clarified. No appreciable magnetodielectric effect was observed in spin reorientation temperature region. On the other hand, below the spin compensation temperature both a dielectric anomaly along the c axis and a concomitant magnetodielectric effect up to ∼ 4% at 80 kOe were observed. This suggests that rare-earth orthoferrites can be another candidate for magnetodielectric system through the mediation of spin compensation phenomena.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics

Confinement quantization of parallel pump instability threshold in a metallic ferromagnetic stripe

M. Kostylev, J.-G. Hu, and R. L. Stamps

Appl. Phys. Lett. 90, 012507 (2007); http://dx.doi.org/10.1063/1.2426970 (3 pages) | Cited 7 times

Online Publication Date: 3 January 2007

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Lateral quantization of an excitation in a confined geometry is shown to lead to multiple cutoff thresholds for parametric processes. This idea is illustrated with a calculation of parallel pump instability thresholds for a ferromagnetic metallic stripe. The lateral quantization by the strip geometry results in thresholds which change discontinuously with increasing stripe width. Magnetostatic interactions create a secondary fine structure of kinks on the threshold curve. This effect should be possible to detect experimentally and be used for precise measurement of microwave losses in patterned magnetic metals.
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75.30.Ds Spin waves
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Highly spin-polarized tunneling in fully epitaxial Co2Cr0.6Fe0.4Al/MgO/Co50Fe50 magnetic tunnel junctions with exchange biasing

Takao Marukame, Takayuki Ishikawa, Shinya Hakamata, Ken-ichi Matsuda, Tetsuya Uemura, and Masafumi Yamamoto

Appl. Phys. Lett. 90, 012508 (2007); http://dx.doi.org/10.1063/1.2428412 (3 pages) | Cited 57 times

Online Publication Date: 4 January 2007

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Fully epitaxial magnetic tunnel junctions (MTJs) with exchange biasing were fabricated with a full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film and a MgO tunnel barrier, where a Co50Fe50 upper electrode was used in a synthetic ferrimagnetic Co50Fe50/Ru/Co90Fe10 trilayer exchange-biased with an IrMn layer through the Co90Fe10/IrMn interface. The fabricated MTJs exhibited clear exchange-biased tunnel magnetoresistance (TMR) characteristics with high TMR ratios of 109% at room temperature and 317% at 4.2 K. A high tunneling spin polarization of 0.88 at 4.2 K was estimated for epitaxial CCFA films with the B2 structure.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.-m Magnetotransport phenomena; materials for magnetotransport
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys

Lattice-mismatch-strain induced inhomogeneities in epitaxial La0.7Ca0.3MnO3 films

Guanyin Gao, Shaowei Jin, and Wenbin Wu

Appl. Phys. Lett. 90, 012509 (2007); http://dx.doi.org/10.1063/1.2429903 (3 pages) | Cited 15 times

Online Publication Date: 4 January 2007

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Epitaxial La0.7Ca0.3MnO3 (LCMO) films of 15–150 nm thick have been grown on SrTiO3(001) [STO(001)] and (LaAlO3)0.3(Sr2AlTaO6)0.7(001) [LSAT(001)] substrates with lattice mismatches of 1.11% and 0.15%, respectively. Asymmetric x-ray reciprocal space mapping was used to determine the strain state evolution in the films. For LCMO/STO(001), as the film thickness increases, at about 30 nm a change from fully to partially strained has been induced, and a further annealing at 900 °C can fully relax the films. For LCMO/LSAT(001), however, due to the negligible lattice mismatch, even at 15 nm the films are almost fully relaxed. Correspondingly, for the fully relaxed LCMO films a paramagnetic to ferromagnetic transition at TC of about 260 K was observed, and for those partially relaxed, both the structure and magnetic transition are inhomogeneous, two thickness-dependent TC were detected for each film. The results show strong evidence that the transition temperature is correlated with the strain state in epitaxial LCMO films.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Gh Other heat and thermomechanical treatments
64.70.K- Solid-solid transitions

Elongated grains in textured substrate tapes and their effect on transport currents in superconductor layers

J. Eickemeyer, D. Selbmann, R. Hühne, H. Wendrock, J. Hänisch, A. Güth, L. Schultz, and B. Holzapfel

Appl. Phys. Lett. 90, 012510 (2007); http://dx.doi.org/10.1063/1.2429905 (3 pages) | Cited 6 times

Online Publication Date: 5 January 2007

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The development of cube textured flexible metallic substrate tapes is of basic interest for the economic production of YBa2Cu3Ox (YBCO) coated superconductors. Nickel tapes microalloyed with silver were prepared with the specific feature of an elongated grain structure. Cube textured NiO films were grown by surface oxidation epitaxy on these tapes retaining the elongated grains. Further, buffer layers and YBCO were deposited thereon. The YBCO layer transports an up to four times higher critical current density (Jc = 2.35 MA/cm2) in the direction of grain elongation compared to the transversal one (Jc = 0.55 MA/cm2).
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74.25.F- Transport properties
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures

Reversible exchange bias and uncompensated magnetization in FexNi1−xF2/Co bilayers

Miyeon Cheon, Zhongyuan Liu, and David Lederman

Appl. Phys. Lett. 90, 012511 (2007); http://dx.doi.org/10.1063/1.2429997 (3 pages) | Cited 7 times

Online Publication Date: 5 January 2007

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The exchange bias of epitaxial (110) FexNi1−xF2/polycrystalline Co bilayers was studied. FexNi1−xF2 is an antiferromagnet with a tunable magnetic anisotropy. A large uncompensated magnetization was observed in the hysteresis loops and its sign was correlated with the sign of the exchange bias. The exchange bias as well as the uncompensated magnetization could be reversed at low temperatures by applying large external fields as a result of the weak magnetic anisotropy of the antiferromagnet. Micromagnetic calculations support the authors’ interpretation of the experimental data. This mechanism is expected to be valid for a wide variety of systems.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Frequency dependence of the nonlinear response in YBa2Cu3O7−x transmission lines

Jordi Mateu, James C. Booth, and Brian H. Moeckly

Appl. Phys. Lett. 90, 012512 (2007); http://dx.doi.org/10.1063/1.2430286 (3 pages) | Cited 4 times

Online Publication Date: 5 January 2007

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The authors evaluate the frequency dependence of the nonlinear response in high-temperature superconductor YBa2Cu3O7−x thin films by simultaneously measuring the nonlinear intermodulation products and harmonic generation in broadband superconducting transmission lines at 76 K. The frequencies of the two-tone incident signal are set to produce spurious signals from 1 to 21 GHz. They extract a nonlinear term ∣ΔR2+jωΔL2∣ by applying a model of spurious signal generation in superconducting transmission lines to their measurement results. They found that this nonlinear term follows a linear dependence on frequency, indicating a dominant contribution of the nonlinear inductance ΔL2 over the nonlinear resistance ΔR2, (ωΔL2⪢ΔR2), for the superconducting nonlinear response.
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74.72.-h Cuprate superconductors
74.78.-w Superconducting films and low-dimensional structures
84.40.Az Waveguides, transmission lines, striplines
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