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28 May 2007

Volume 90, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 90, 221101 (2007); http://dx.doi.org/10.1063/1.2743884 (3 pages)

Siyka I. Shopova, Hongying Zhou, Xudong Fan, and Po Zhang
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Enhancement of photoinduced effects in Bi1−xCaxMnO3 thin films

V. N. Smolyaninova, E. Talanova, Rajeswari M. Kolagani, G. Yong, R. Kennedy, M. Steger, D. Schaefer, and K. Wall

Appl. Phys. Lett. 90, 222501 (2007); http://dx.doi.org/10.1063/1.2743948 (3 pages)

Online Publication Date: 30 May 2007

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A considerable increase of the photoinduced resistivity changes and the lifetime of these changes were found in the Bi0.4Ca0.6MnO3 thin films after depositing gold nanoparticles on the surface. A possible interpretation of this effect may be the enhancement of local electromagnetic field at the interface between the film and the metal nanoparticles due to the plasmon resonance, which may promote formation of larger volume of conducting phase producing larger magnitude and the lifetime of photoinduced resistivity changes.
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73.61.Ng Insulators
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Colossal electroresistance without colossal magnetoresistance in La0.9Sr0.1MnO3

N. Biškup, A. de Andrés, N. M. Nemes, M. García-Hernandez, K. V. Glazyrin, and Y. M. Mukovskii

Appl. Phys. Lett. 90, 222502 (2007); http://dx.doi.org/10.1063/1.2745220 (3 pages) | Cited 7 times

Online Publication Date: 31 May 2007

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The authors report on colossal electroresistance (ER) in the ferromagnetic insulator manganite La0.9Sr0.1MnO3. The single crystal samples exhibit a transition into a low resistive state above a certain threshold current. Pulsed measurements demonstrate that this transition is not a consequence of heating. ER behaves similarly to magnetoresistance (MR) above the orbital order temperature TOO. Below TOO the MR is only 20% while ER enhances the conductivity by several orders of magnitude. Magnetic field and electric current have opposite effects on the conductivity, therefore, it seems that only the injected carriers are able to modify the ordering of eg Mn orbitals.
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72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Sk Insulators
75.50.Dd Nonmetallic ferromagnetic materials

Signatures of enhanced ordering temperatures in digital superlattices of (LaMnO3)m/(SrMnO3)2m

A. Bhattacharya, X. Zhai, M. Warusawithana, J. N. Eckstein, and S. D. Bader

Appl. Phys. Lett. 90, 222503 (2007); http://dx.doi.org/10.1063/1.2745205 (3 pages) | Cited 26 times

Online Publication Date: 31 May 2007

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Digital superlattices of (LaMnO3)m/SrMnO3)2m (m ⩽ 3) having the same nominal composition as La1/3Sr2/3MnO3, an antiferromagnetic insulator, have been synthesized by means of molecular beam epitaxy. All superlattices show a sharp resistive maximum at temperatures near to or higher than the Néel temperature of bulk La1/3Sr2/3MnO3. No discernible signatures of magnetic ordering are observed near the resistivity peak for m ⩽ 2, but m = 3 has a susceptibility peak consistent with antiferromagnet ordering, which is canted when cooled in a small magnetic field. Analogies are drawn to dx2−y2 orbitally ordered, layered antiferromagnetic manganites to explain the observations.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
73.63.-b Electronic transport in nanoscale materials and structures

Temperature- and magnetic-field-induced phase transitions in Fe-rich FePt alloys

Chuan-Bing Rong and J. Ping Liu

Appl. Phys. Lett. 90, 222504 (2007); http://dx.doi.org/10.1063/1.2745255 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2007

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Structural and magnetic properties of the FexPt100−x (x = 78–88) alloys have been investigated. It is found that for all of the investigated compositions, a phase transition occurs from the disordered γ phase to the ordered α phase during cooling, while a reverse process takes place during heating. Moreover, magnetic fields also induce a phase transition from the γ phase to the α phase near the transition temperature. The temperature- and magnetic-field-induced phase transitions give rise to a huge negative thermal expansion and thus a giant magnetic entropy change (up to 39.8 J/kg K for the alloy with x = 79). The contribution of the magnetic field induced phase transition to the total magnetic entropy change is estimated to be around 20%–25%.
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75.30.Sg Magnetocaloric effect, magnetic cooling
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.)
81.40.Gh Other heat and thermomechanical treatments
75.50.Bb Fe and its alloys

Effects of hydrogenated annealing on structural defects, conductivity, and magnetic properties of V-doped ZnO powders

S. H. Liu, H. S. Hsu, C. R. Lin, C. S. Lue, and J. C. A. Huang

Appl. Phys. Lett. 90, 222505 (2007); http://dx.doi.org/10.1063/1.2745642 (3 pages) | Cited 20 times

Online Publication Date: 1 June 2007

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The structure, electrical property, and magnetism of 7.5% V-doped ZnO powders that were hydrogenated annealed at 300, 500, and 700 °C have been systematically investigated. The saturation magnetization and conductivity of the V:ZnO powders increase with hydrogenated annealing temperature (Tha), and the magnetization-temperature curves transform from paramagnetism to weak ferromagnetism ( ∼ 10−4μB/V atom) as Tha increases. The results suggest that ferromagnetism in V:ZnO powders is highly correlated to the structural defects.
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75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.80.Ey III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Theory for symmetric toggle magnetic random access memory

D. C. Worledge, P. L. Trouilloud, and W. J. Gallagher

Appl. Phys. Lett. 90, 222506 (2007); http://dx.doi.org/10.1063/1.2743899 (3 pages) | Cited 10 times

Online Publication Date: 1 June 2007

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The authors analyze the critical switching curve for two identical coupled magnetic free layers, as used in toggle magnetic random access memory. The continuous and discontinuous transitions between different magnetic states are described. A general criteria for toggling is derived by summing up the number of clockwise and counterclockwise transitions, leading to a larger toggle region than previously reported. It also leads to a significant chirality effect, wherein the toggle region shifts depending on the order in which the word and bit line fields are applied. Finally, the authors discuss a type of switching useful for experimentally measuring the critical switching curve.
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85.75.Dd Magnetic memory using magnetic tunnel junctions
85.70.Ay Magnetic device characterization, design, and modeling
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
84.30.Sk Pulse and digital circuits
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