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7 Jun 2010

Volume 96, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 96, 231104 (2010); http://dx.doi.org/10.1063/1.3443734 (3 pages)

Hiroto Sekiguchi, Katsumi Kishino, and Akihiko Kikuchi
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Asymmetrical giant magnetoimpedance in exchange-biased NiFe

C. García, J. M. Florez, P. Vargas, and C. A. Ross

Appl. Phys. Lett. 96, 232501 (2010); http://dx.doi.org/10.1063/1.3446894 (3 pages) | Cited 5 times

Online Publication Date: 7 June 2010

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Linear asymmetrical magnetoimpedance (MI) has been obtained in thin multilayer strips of exchange-coupled FeNi(5 nm)/IrMn(15 nm)/FeNi(40 nm)/Cu(100 nm)/FeNi(40 nm)/IrMn(15 nm)/FeNi(5 nm), in which the MI response is enhanced by including a Cu layer between the two 40 nm NiFe layers. The antiferromagnetic layer creates an exchange bias that shifts both the hysteresis loop and the MI response. The asymmetrical MI peak positions are shifted to higher magnetic field as the probe frequency increases. Linear MI behavior can be tuned around zero external field without the need for external biasing fields or additional coils, by changing the frequency. The impedance of a planar magnetic conductor was modeled based on a modified Stoner–Wohlfarth energy density.
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75.47.De Giant magnetoresistance
72.15.Gd Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Negative magnetoresistance in a V3+/V4+ mixed valent vanadate

A. Maignan, O. I. Lebedev, G. Van Tendeloo, C. Martin, and S. Hébert

Appl. Phys. Lett. 96, 232502 (2010); http://dx.doi.org/10.1063/1.3446892 (3 pages)

Online Publication Date: 8 June 2010

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The magnetotransport and magnetic properties of the PbV6O11 vanadate, crystallizing in the P63mc space group, reveal the existence of a negative magnetoresistance related to its ferromagnetic state (TC ∼ 90 K). The maximum effect is observed at 20 K reaching −30% in 9 T. The structural study of this ceramic reveals a V/Pb ratio smaller than expected from the formula. This is explained by the presence of numerous stacking faults observed by high resolution transmission electron microscopy. The existence of these planar defects acting as resistive barriers along the c axis could be responsible for tunneling magnetoresistance.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
61.72.Nn Stacking faults and other planar or extended defects
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
75.50.Dd Nonmetallic ferromagnetic materials

La-doped EuO: A rare earth ferromagnetic semiconductor with the highest Curie temperature

H. Miyazaki, H. J. Im, K. Terashima, S. Yagi, M. Kato, K. Soda, T. Ito, and S. Kimura

Appl. Phys. Lett. 96, 232503 (2010); http://dx.doi.org/10.1063/1.3416911 (3 pages) | Cited 14 times

Online Publication Date: 9 June 2010

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We report the fabrication of single-crystalline La-doped EuO thin films with a Curie temperature (TC) of about 200 K, the highest among rare-earth compounds without transition metals. From first-principle band calculation and x-ray diffraction measurement, the observed increase in TC cannot be explained only by the increase in hybridization intensity due to lattice contraction and the increase in up-spin electrons of the Eu 5d state caused by the electron doping. Hybridization between the Eu 4f and donor states and/or Ruderman–Kittel–Kasuya–Yoshida interaction mediated by the doped La 5d state is a possible origin of the increase in TC.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Et Exchange and superexchange interactions

Oxygen vacancy controlled tunable magnetic and electrical transport properties of (Li, Ni)-codoped ZnO thin films

E. Senthil kumar, S. Venkatesh, and M. S. Ramachandra Rao

Appl. Phys. Lett. 96, 232504 (2010); http://dx.doi.org/10.1063/1.3449122 (3 pages) | Cited 5 times

Online Publication Date: 9 June 2010

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We investigated the electrical, magnetic, and magnetotransport properties of Li–Ni codoped ZnO thin films in the electron dominated, hole dominated, and insulating regimes. In a narrow window of oxygen growth pressure, 10−3–10−2 mbar, the films exhibited p-type conductivity with a maximum hole concentration ∼ 8.2×1017 cm−3. Magnetoresistance exhibited by the films is attributed to scattering of charge carriers due to localized magnetic moments. Insulating films showed superparamagnetic behavior, whereas both n-type and p-type films showed room temperature ferromagnetism. Our findings suggest that oxygen vacancies and Ni ions in cation site are jointly responsible for ferromagnetism that is not dependent on the carrier type.
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72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ga II-VI semiconductors
68.55.ag Semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities

Room temperature ferromagnetism in pristine MgO thin films

C. Moyses Araujo, Mukes Kapilashrami, Xu Jun, O. D. Jayakumar, Sandeep Nagar, Yan Wu, Cecilia Århammar, Börje Johansson, Lyubov Belova, Rajeev Ahuja, Gillian A. Gehring, and K. V. Rao

Appl. Phys. Lett. 96, 232505 (2010); http://dx.doi.org/10.1063/1.3447376 (3 pages) | Cited 22 times

Online Publication Date: 10 June 2010

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Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm3 is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.
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75.30.Hx Magnetic impurity interactions
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Impedance spectroscopy of micron sized magnetic tunnel junctions with MgO tunnel barrier

Snorri Ingvarsson, Mustafa Arikan, Matthew Carter, Weifeng Shen, and Gang Xiao

Appl. Phys. Lett. 96, 232506 (2010); http://dx.doi.org/10.1063/1.3449573 (3 pages) | Cited 3 times

Online Publication Date: 11 June 2010

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We have studied the magnetoimpedance of micron sized magnetic tunnel junction sensors with 1.7 nm MgO tunnel barrier. We performed ac impedance spectroscopy in the frequency range between 100 Hz–40 MHz as a function of applied magnetic field in the sensing direction. We model our devices with a simple RLC circuit. Fitting the model to our data results in frequency independent R, L, and C, and our low frequency results are in agreement with dc measurements. Despite excellent agreement with published result on interface capacitance for MgO barrier magnetic tunnel junctions similar to ours we do not observe any magnetocapacitance in our devices.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
75.47.-m Magnetotransport phenomena; materials for magnetotransport

Electron spin resonance probed suppressing of the cycloidal spin structure in doped bismuth ferrites

J. W. Lin, Y. H. Tang, C. S. Lue, and J. G. Lin

Appl. Phys. Lett. 96, 232507 (2010); http://dx.doi.org/10.1063/1.3451463 (3 pages) | Cited 5 times

Online Publication Date: 11 June 2010

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The weak magnetism of bismuth ferrites Bi1−xDyxFeO3 with x = 0.0 to 0.40 is studied via the electron spin resonance (ESR) of X-band (9.53 GHz) at various temperatures. The g-factor of pure BiFeO3 is 2.0, which originates from its cycloidal spin structure; while for the doped Bi1−xDyxFeO3 samples with x>0.10, ESR spectra reveal a second phase with a different g-factor around 1, which is attributed to the homogeneous magnetized phase of Bi1−xDyxFeO3. The temperature dependent ESR data further suggest a picture of the doping-induced transformation from cycloidal to canted antiferromagnetic state.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
76.30.-v Electron paramagnetic resonance and relaxation
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics

Correlation between local structure distortions and martensitic transformation in Ni–Mn–In alloys

D. N. Lobo, K. R. Priolkar, P. A. Bhobe, D. Krishnamurthy, and S. Emura

Appl. Phys. Lett. 96, 232508 (2010); http://dx.doi.org/10.1063/1.3454277 (3 pages) | Cited 4 times

Online Publication Date: 11 June 2010

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The local structural distortions arising as a consequence of increasing Mn content in Ni2Mn1+xIn1−x (x = 0, 0.3, 0.4, 0.5, and 0.6) and its effect on martensitic transformation have been studied using extended x-ray absorption fine structure (EXAFS) spectroscopy. Using the room temperature EXAFS at the Ni and Mn K-edges in the above compositions, the changes associated with respect to the local structure of these absorbing atoms are compared. It is seen that in the alloys exhibiting martensitic transformation (x ≥ 0.4) there is a significant difference between the Ni–In and Ni–Mn bond lengths even in the austenitic phase indicating atomic volume to be the main factor in inducing martensitic transformation in Ni–Mn–In Heusler alloys.
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64.70.kd Metals and alloys
61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra
61.50.Lt Crystal binding; cohesive energy
81.30.Kf Martensitic transformations
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