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29 Aug 2005

Volume 87, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 87, 093109 (2005); http://dx.doi.org/10.1063/1.2035332 (3 pages)

J. Noborisaka, J. Motohisa, S. Hara, and T. Fukui
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Enhancement of the magnetic properties in (Ga1−xMnx)N thin films due to Mn-delta doping

H. C. Jeon, T. W. Kang, T. W. Kim, Joongoo Kang, and K. J. Chang

Appl. Phys. Lett. 87, 092501 (2005); http://dx.doi.org/10.1063/1.2032587 (3 pages) | Cited 17 times

Online Publication Date: 22 August 2005

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The effects of Mn delta-doping on the magnetic properties of (Ga1−xMnx)N thin films grown on GaN buffer layers by molecular-beam epitaxy were studied. The magnetization curve as a function of the magnetic field as 5 K indicated that ferromagnetisms existed in the Mn delta-doped (Ga1−xMnx)N and (Ga1−xMnx)N thin films and that the magnetization in the Mn delta-doped (Ga1−xMnx)N thin film was significantly enhanced. The magnetization curve as a function of the temperature showed that the Curie temperature of the Mn delta-doped (Ga1−xMnx)N thin film was estimated to be above room temperature. The increase of the magnetization in the Mn delta-doped (Ga1−xMnx)N thin film in comparison with that in the (Ga1−xMnx)N thin film was attributed to the enhancement of the carrier-mediated ferromagnetism due to increased hole concentrations. The theoretical results showed that Ga vacancies near the Mn delta-doping layer were likely to cause p-type conductance, indicating that the enhancement of the magnetic properties in (Ga1−xMnx)N thin films originated from Mn delta doping.
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75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.J- Point defects and defect clusters

Charge sensitivity of the inductive single-electron transistor

Mika A. Sillanpää, Leif Roschier, and Pertti J. Hakonen

Appl. Phys. Lett. 87, 092502 (2005); http://dx.doi.org/10.1063/1.2034096 (3 pages)

Online Publication Date: 22 August 2005

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We calculate the charge sensitivity of a recently demonstrated device where the Josephson inductance of a single Cooper-pair transistor is measured. We find that the intrinsic limit to detector performance is set by oscillator quantum noise. Sensitivity better than 10−6 e/math is possible with a high Q value ∼ 103, or using a superconducting quantum interference device amplifier. The model is compared to experiment, where charge sensitivity 3×10−5 e/math and bandwidth 100 MHz are achieved.
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85.35.Gv Single electron devices
85.25.Cp Josephson devices

Terahertz surface impedance of epitaxial MgB2 thin film

B. B. Jin, P. Kuzel, F. Kadlec, T. Dahm, J. M. Redwing, A. V. Pogrebnyakov, X. X. Xi, and N. Klein

Appl. Phys. Lett. 87, 092503 (2005); http://dx.doi.org/10.1063/1.2034107 (3 pages) | Cited 10 times

Online Publication Date: 22 August 2005

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We report on terahertz (THz) surface impedance measurement of an epitaxial MgB2 thin film using time domain THz spectroscopy. We show that the surface resistance of the MgB2 film is much lower than that of YBa2Cu3O7−δ and copper in the THz range. A linear dependence of the surface reactance on frequency is observed, yielding a penetration depth of about 100 nm at low temperatures. The measurements agree qualitatively with calculations based on impurity scattering in the Born limit. Our results clearly indicate that MgB2 thin films have a great potential for THz electronic applications.
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74.78.-w Superconducting films and low-dimensional structures
74.70.-b Superconducting materials other than cuprates
74.25.N- Response to electromagnetic fields
74.25.F- Transport properties
74.25.Ha Magnetic properties including vortex structures and related phenomena
73.50.Mx High-frequency effects; plasma effects
74.25.Gz Optical properties
78.47.-p Spectroscopy of solid state dynamics

β-phase-domain-free α‐MnAs thin films on GaAs(001) by postgrowth annealing

J. H. Song, Y. Cui, J. J. Lee, and J. B. Ketterson

Appl. Phys. Lett. 87, 092504 (2005); http://dx.doi.org/10.1063/1.2035316 (3 pages) | Cited 3 times

Online Publication Date: 23 August 2005

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Postgrowth annealing effects on a heteroepitaxial MnAs thin film grown on a GaAs(001) substrate have been investigated. The β‐MnAs phase domains of an as-grown sample, observed as dark stripes in the surface topography at room temperature, disappear completely after postgrowth annealing. In support of this finding, the paramagnetic contribution to the magnetic hysteresis loop arising from the β‐MnAs phase domains is also not observed at 300 K. We attribute the origin of these effects to relaxation of the elastic strain in the MnAs thin film.
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75.50.Dd Nonmetallic ferromagnetic materials
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology

Structural and magnetic properties of epitaxially grown MnAs films on GaAs(110)

D. Kolovos-Vellianitis, C. Herrmann, L. Däweritz, and K. H. Ploog

Appl. Phys. Lett. 87, 092505 (2005); http://dx.doi.org/10.1063/1.2035328 (3 pages) | Cited 12 times

Online Publication Date: 23 August 2005

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MnAs films were grown by molecular beam epitaxy (MBE) on GaAs(110) substrates, since this orientation was recently identified as promising for the increase of spin lifetimes in semiconductor heterojunctions, which is of interest in spin injection experiments. A single epitaxial orientation was revealed for the MnAs films which consist of both the ferromagnetic, hexagonal α‐MnAs and the paramagnetic, orthorhombic β‐MnAs phase at room temperature. This phase coexistence could be imaged as a well ordered stripe pattern, whose periodicity depends on the film thickness. The study of the ferromagnetic properties shows a strong influence of the film thickness on the measured coercive fields and saturation magnetizations.
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75.70.Ak Magnetic properties of monolayers and thin films
75.20.Ck Nonmetals
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Large exchange bias and high stability of CoFe/CrPt films with L10 CrPt as the pinning layer

B. Dai, J. W. Cai, W. Y. Lai, Y. K. An, Z. H. Mai, F. Shen, Y. Z. Liu, and Z. Zhang

Appl. Phys. Lett. 87, 092506 (2005); http://dx.doi.org/10.1063/1.2035887 (3 pages) | Cited 5 times

Online Publication Date: 24 August 2005

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We have studied an antiferromagnetic L10 CrPt film as a pinning layer. dc magnetron sputtered [Pt/Cr] multilayers on a Co0.9Fe0.1 layer exhibit no exchange bias. After being annealed at 350 °C for 5 h in a vacuum, the equiatomic [Pt/Cr] multilayer stack is transformed into a uniform CrPt alloy film with L10 phase, which pins the adjacent 120 Å CoFe layer with a pinning field of ∼ 70 Oe and a coercivity of only 28 Oe. The hysteresis loop of this exchange biased system is almost square and the interdiffusion between the CrPt and the CoFe layers is rather small. The equivalent interface exchange energy ΔE, 0.12 erg/cm2, is comparable to the typical value of FeMn biasing system. However, the blocking temperature, at which the exchange bias disappears, is as high as 600 °C, 150 °C higher than the highest value ever reported. Since it possesses extremely good thermal stability, large exchange bias, little interdiffusion, and high corrosion resistance, the antiferromagnetic CrPt film is proposed to serve as a pinning layer for magnetoresistive devices.
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66.30.Ny Chemical interdiffusion; diffusion barriers
75.50.Ee Antiferromagnetics
75.50.Bb Fe and its alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.65.Kn Corrosion protection
81.40.Gh Other heat and thermomechanical treatments
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