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11 Feb 2008

Volume 92, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 92, 063101 (2008); http://dx.doi.org/10.1063/1.2839572 (3 pages)

M. N. Ou, T. J. Yang, S. R. Harutyunyan, Y. Y. Chen, C. D. Chen, and S. J. Lai
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Surface ferromagnetism and exchange bias in vacuum annealed Co3−yZnyO4 films

C. Sudakar, P. Kharel, G. Lawes, R. Suryanarayanan, R. Naik, and V. M. Naik

Appl. Phys. Lett. 92, 062501 (2008); http://dx.doi.org/10.1063/1.2836792 (3 pages) | Cited 7 times

Online Publication Date: 11 February 2008

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We report on the structural and the magnetic properties of spin coated Co3−yZnyO4 thin films. The microstructure of high vacuum annealed films exhibit a crystalline Zn:CoO core with a disordered oxygen deficient amorphous Co:ZnO surface. Weak ferromagnetism (m ∼ 15 mμB/Co) and an exchange bias (HE ∼ 500 Oe) are observed at 10 K despite the absence of any Co metal clusters. HE is smaller for samples with smaller Zn fractions (for Co3O4-HV, HE ∼ 250 Oe). Adding Zn significantly enhances HE. The exchange anisotropy in an antiferromagnetic material due to surface disordered weak ferromagnetism and its overall implications to dilute magnetic semiconducting oxides are discussed.
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75.70.Rf Surface magnetism
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
68.55.J- Morphology of films
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials

Magnetic properties of Heusler compounds Ru2CrGe and Ru2CrSn

Hironari Okada, Keiichi Koyama, Kazuo Watanabe, Yosuke Kusakari, Takeshi Kanomata, and Hironori Nishihara

Appl. Phys. Lett. 92, 062502 (2008); http://dx.doi.org/10.1063/1.2841654 (3 pages) | Cited 3 times

Online Publication Date: 11 February 2008

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We have succeeded in synthesizing the Heusler compounds Ru2CrGe and Ru2CrSn and performed magnetization measurements in high magnetic fields up to 18 T in order to investigate the magnetic properties of Ru2CrGe and Ru2CrSn. We confirmed that the compounds have an ordered Heusler L21 structure. It was found that Ru2CrGe is an antiferromagnet with the Néel temperature TN = 13 K and Ru2CrSn shows a spin-glass-like behavior below 7 K. The Heisenberg exchange constants determined on the basis of the experimental results for Ru2CrGe are different from the values of Mn-based Heusler compounds.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.50.Lk Spin glasses and other random magnets

Interfacial potential in La1−xCaxMnO3/SrTiO3:Nb junctions with different Ca contents

W. M. Lü, J. R. Sun, D. J. Wang, Y. W. Xie, S. Liang, Y. Z. Chen, and B. G. Shen

Appl. Phys. Lett. 92, 062503 (2008); http://dx.doi.org/10.1063/1.2841643 (3 pages) | Cited 10 times

Online Publication Date: 11 February 2008

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Manganite-based heterojunctions La1−xCaxMnO3/SrTiO3:Nb (0.05 wt %) with x = 0.1, 0.2, 0.33, 0.65, 0.75, and 1 have been fabricated, and the effects of Ca content on the interfacial potential are experimentally studied. Rectifying behavior well described by the Shockley equation is observed, and the interfacial potential (VD) is obtained for all of the junctions based on an analysis of the current-voltage characteristics. The most remarkable result of the present work is the strong dependence of the interfacial potential on the carrier content of La1−xCaxMnO3 films: VD increases monotonously from ∼ 0.6 to  ∼ 1.1 V as x sweeps from 0.1 to 1. Influence on VD of the Fermi energy and Jahn–Teller effect in La1−xCaxMnO3 films are discussed.
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75.47.Gk Colossal magnetoresistance
75.47.Lx Magnetic oxides
73.40.Ei Rectification
73.20.At Surface states, band structure, electron density of states
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Effects of perpendicular anisotropy on the interlayer coupling in perpendicularly magnetized [Pd/Co]/Cu/[Co/Pd] spin valves

Naganivetha Thiyagarajah, Seongtae Bae, Ho Wan Joo, Young Chul Han, and Jongryoul Kim

Appl. Phys. Lett. 92, 062504 (2008); http://dx.doi.org/10.1063/1.2839596 (3 pages) | Cited 14 times

Online Publication Date: 12 February 2008

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The effects of perpendicular anisotropy on the interlayer coupling in perpendicularly magnetized [Pd/Co]/Cu/[Co/Pd] spin valves have been explored. It was clearly confirmed that the perpendicular anisotropy of soft and hard [Co/Pd] multilayers plays a crucial role in determining the physical characteristics of perpendicular interlayer coupling in the [Pd/Co]/Cu/[Co/Pd] spin valves. In addition, theoretical calculations demonstrated that the behavior of experimentally observed perpendicular interlayer coupling dominantly followed a Ruderman–Kittel–Kasuya–Yoshida oscillation modified by including a physical parameter directly relevant to the angle deviation of soft or hard [Co/Pd] magnetizations from the perpendicular direction in the spin valves rather than a topologically induced interlayer coupling.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.47.De Giant magnetoresistance

Large magnetization in high Gd concentration GaGdN and Si-doped GaGdN grown at low temperatures

Yi Kai Zhou, Sung Woo Choi, Shuichi Emura, Shigehiko Hasegawa, and Hajime Asahi

Appl. Phys. Lett. 92, 062505 (2008); http://dx.doi.org/10.1063/1.2841657 (3 pages) | Cited 13 times

Online Publication Date: 12 February 2008

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GaGdN layers were grown at temperatures below 300 °C by radio-frequency plasma-assisted molecular-beam epitaxy on sapphire substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained. X-ray diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth at low temperatures. Local structure around the Gd atom was investigated by extended x-ray absorption fine structure measurement using Gd LIII edge. It was shown that Gd atoms were mainly incorporated into the Ga sites in the GaGdN layers. All the samples grown at low temperatures exhibited ferromagnetic characteristics. It is considerable that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism occurs in the low-temperature-grown GaGdN. Furthermore, Si was doped into GaGdN layers during growth in order to increase carrier density, and larger magnetization was observed.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
78.70.Dm X-ray absorption spectra
64.75.Qr Phase separation and segregation in semiconductors

Spin reorientation transition of ferromagnetic nanowires with perpendicular magnetic anisotropy

Sug-Bong Choe

Appl. Phys. Lett. 92, 062506 (2008); http://dx.doi.org/10.1063/1.2857542 (3 pages) | Cited 9 times

Online Publication Date: 14 February 2008

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We present an analytic theory of the magnetization phase in ferromagnetic nanowires with perpendicular magnetic anisotropy. In nanowire geometry, the shape anisotropy is reduced considerably in contrast to continuous films. Consequently, the spin reorientation transition occurs from in plane to out of plane with respect to the wire width. The stable domain size in the out-of-plane phase is sensitive to the wire width and approaches the single domain state on narrowing the width further. A phase diagram of the three phases is proposed with respect to the wire width and the saturation magnetization.
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61.46.-w Structure of nanoscale materials
75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves
75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Half-metallic electronic structures of quaternary ferromagnetic chalcospinels: CdxCu1−xCr2S4 and CdxCu1−xCr2Se4

Y.-H. A. Wang, A. Gupta, M. Chshiev, and W. H. Butler

Appl. Phys. Lett. 92, 062507 (2008); http://dx.doi.org/10.1063/1.2841848 (3 pages) | Cited 14 times

Online Publication Date: 15 February 2008

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First-principles calculations indicate that the chalcogenide spinels CdxCu1−xCr2S4 and CdxCu1−xCr2Se4 can be ferromagnetic metals, half-metals, or semiconductors depending on the Cd concentration x. In particular, CdxCu1−xCr2S4 can be tuned to be effectively half-metallic for x values between 0.25 and 0.875 and CdxCu1−xCr2Se4 can be half-metallic for x between 0.625 and 0.875. For x<0.25 for CdxCu1−xCr2S4 and for x<0.625 for CdxCu1−xCr2Se4, these materials are predicted to be ferromagnetic metals. For x>0.875 both systems are predicted to be ferromagnetic semiconductors.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Optical magnetoelectric effect at CaRuO3–CaMnO3 interfaces as a polar ferromagnet

Hiroyuki Yamada, H. Sato, H. Akoh, N. Kida, T. Arima, M. Kawasaki, and Y. Tokura

Appl. Phys. Lett. 92, 062508 (2008); http://dx.doi.org/10.1063/1.2857466 (3 pages) | Cited 4 times

Online Publication Date: 15 February 2008

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A correlated electron interface between paramagnetic CaRuO3 and antiferromagnetic CaMnO3 has been characterized with optical magnetoelectric (OME) effect as an interface-selective probe for spin and charge states. To detect the OME effect, i.e., nonreciprocal directional dichroism for visible or near-infrared light, we have constructed a “tricolor” superlattice with artificially broken inversion symmetry by stacking CaRuO3, CaMnO3, and CaTiO3, and patterned a grating structure with 4 μm period on the superlattice. The observed intensity modulation (0.3% at 50 K) in the Bragg diffraction verifies a charge transfer and concomitant ferromagnetism at the CaRuO3–CaMnO3 interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
75.50.Ee Antiferromagnetics
78.20.Fm Birefringence

Ferromagnetism in Cu-doped ZnO films: Role of charge carriers

Ashutosh Tiwari, Michael Snure, Dhananjay Kumar, and Jeremiah T. Abiade

Appl. Phys. Lett. 92, 062509 (2008); http://dx.doi.org/10.1063/1.2857481 (3 pages) | Cited 44 times

Online Publication Date: 15 February 2008

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We report the observation of room temperature ferromagnetism in Cu-doped (5%) ZnO films grown on c-plane sapphire substrates. Films were prepared by pulsed laser deposition technique and were thoroughly characterized using several state-of-the-art characterization techniques. Hall measurements showed that the films are of n-type with a carrier concentration of 3×1017 cm−3. Magnetization measurements showed that the films exhibit room temperature ferromagnetism with a saturation magnetization of ∼ 1.45μB/Cu atom. When additional carriers were introduced in the films, ferromagnetism was completely vanished. Our results show that the p-type nature of the film is not essential for realizing ferromagnetic characteristics; however, the concentration of n-type carriers should not exceed a critical value.
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68.55.ag Semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Fg Pulsed laser ablation deposition
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ga II-VI semiconductors
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