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15 Mar 1999

Volume 74, Issue 11, pp. 1507-1635

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Surface pattern and large low-field magnetoresistance in La0.5Ca0.5MnO3 films

H. B. Peng, B. R. Zhao, Z. Xie, Y. Lin, B. Y. Zhu, Z. Hao, Y. M. Ni, H. J. Tao, X. L. Dong, and B. Xu

Appl. Phys. Lett. 74, 1606 (1999); http://dx.doi.org/10.1063/1.123631 (3 pages) | Cited 14 times

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Formation of an ordered surface structure in La0.5Ca0.5MnO3 films due to the mismatch of the thermal expansion coefficient between the film and the substrate has been investigated. The surface pattern consists of grain chains located on regular orthogonal cracks. The cracks serve as weak-link grain boundaries, and unusually enhanced low-field magnetoresistance (−14.4% in 400 Oe at 90 K) has been observed, which may be explained by spin-polarized tunneling across the grain boundaries. © 1999 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
65.40.De Thermal expansion; thermomechanical effects
61.72.Mm Grain and twin boundaries

Dynamic scaling of magnetic hysteresis in micron-sized Ni80Fe20 disks

W. Y. Lee, B.-Ch. Choi, J. Lee, C. C. Yao, Y. B. Xu, D. G. Hasko, and J. A. C. Bland

Appl. Phys. Lett. 74, 1609 (1999); http://dx.doi.org/10.1063/1.123632 (3 pages) | Cited 16 times

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The scaling of the magnetic hysteresis loop area of permalloy disks (20–400 μm diam) has been studied as a function of applied field amplitude H0 and frequency Ω using scanning Kerr microscopy. An increase in the dynamic coercivity with reduced size is observed for d<100 μm in the frequency range studied (0.1–800 Hz). However, the loop area A follows the scaling relation A∝H0αΩβ, with α ≈ 0.14 and β ≈ 0.50 throughout the entire size range studied. Our results demonstrate that the dynamic scaling behavior is universal even though the lateral size influences the domain structure and magnetic reversal behavior. © 1999 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
78.20.Ls Magneto-optical effects
75.60.Ch Domain walls and domain structure

Theory of magnesium/Alq3 interaction in organic light emitting devices

R. Q. Zhang, X. Y. Hou, and S. T. Lee

Appl. Phys. Lett. 74, 1612 (1999); http://dx.doi.org/10.1063/1.123633 (3 pages) | Cited 24 times

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The interaction between the magnesium (Mg) atom and Alq3 molecule in organic light emitting devices has been theoretically studied using the PM3 method of the molecular orbital theory. It has been shown that various interactions can happen when the Mg atom approaches the Alq3 molecule, leading to significant changes in the molecular geometry and electronic structure of Alq3. The resulting configurations with insertion of Mg into the central part of the Alq3 molecule are found to be energetically more favorable than those with Mg forming bond(s) with a benzene ring of Alq3. In agreement with recent experiments, this result shows that the interaction between Mg and the Alq3 molecule depends on the order of deposition. Interestingly, the density of states calculated for these systems reveals that the creation of the new electronic gap states observed in the experiments is mainly relating to the aluminum atomic orbital due to interaction, instead of a direct contribution of Mg. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
71.20.Rv Polymers and organic compounds
33.15.Bh General molecular conformation and symmetry; stereochemistry

Effect of three-dimensional strain states on magnetic anisotropy of La0.8Ca0.2MnO3 epitaxial thin films

T. K. Nath, R. A. Rao, D. Lavric, C. B. Eom, L. Wu, and F. Tsui

Appl. Phys. Lett. 74, 1615 (1999); http://dx.doi.org/10.1063/1.123634 (3 pages) | Cited 79 times

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Magnetic anisotropy of La0.8Ca0.2MnO3 (LCMO) epitaxial thin films grown on (001) SrTiO3 and LaAlO3 a substrates exhibits strong correlation with substrate-induced strain states as determined by normal and grazing incidence x-ray diffraction. In a 250 Å thick LCMO (001)T film grown on SrTiO3 substrate, an in-plane biaxial magnetic anisotropy is observed, and it is accompanied by a substrate-induced in-plane biaxial tensile strain. In contrast, the observed magnetic easy axis for a 250 Å (110)T film grown on LaAlO3 substrate is perpendicular to the film plane, and the corresponding in-plane strain is biaxial compressive. In both cases the magnetic easy axes are along the crystallographic directions under tensile strain, indicating the presence of a positive magnetostriction. In thicker films (∼4000 Å) grown on both substrates that are nearly strain relaxed, the magnetic easy axis lies in the film plane along the [110] direction of the (001) substrate. © 1999 American Institute of Physics.
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75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
75.80.+q Magnetomechanical effects, magnetostriction

90° magneto-optical polar Kerr effect in layered magnetic semiconductor/metal structures

Yu. A. Uspenskii and B. N. Harmon

Appl. Phys. Lett. 74, 1618 (1999); http://dx.doi.org/10.1063/1.123635 (3 pages) | Cited 3 times

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Using analytical and numerical methods, we show that the polar Kerr rotation θK of 90° may be attained in a large class of (magnetic-semiconductor)/metal layered structures just below the absorption edge. The corresponding reflectivity varies over wide limits. For example, in a EuS/Ag multilayer with a small period it is of several percent, while in a thick layer of EuS deposited on Ag it achieves 95%. © 1999 American Institute of Physics.
Show PACS
78.20.Ls Magneto-optical effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
78.66.Li Other semiconductors
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