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31 Jan 2000

Volume 76, Issue 5, pp. 523-656

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Observation of an antiparallel magnetic state in Fe3O4/Mn3O4 superlattices

G. Chern, Lance Horng, T. Y. Hou, and M. Z. Lin

Appl. Phys. Lett. 76, 598 (2000); http://dx.doi.org/10.1063/1.125829 (3 pages) | Cited 7 times

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[Fe3O4(20 Å)/Mn3O4(80 Å)]x20 and [Fe3O4(20 Å)/MgO(80 Å)]x20 superlattices on MgO(001) are fabricated by molecular beam epitaxy in order to compare the magnetic coupling in ferrimagnetic–ferrimagnetic and ferrimagnetic–nonmagnetic systems. The magnetic response is measured as a function of applied-field (−50 to 50 kOe) parallel to the film surface and temperature (5–300 K). A strong reduction of magnetization, from 115 to 45 emu/cm3, is observed only from the Fe3O4/Mn3O4 superlattice at temperature below ∼60 K. This observation indicates that the magnetic moments in two constituents are antiparallel and the Curie temperature (Tc) of Mn3O4 is enhanced for 15 K. In addition, the remanent magnetization shows a compensation point (Tcp) at about 32 K at which the opposing spins are balanced. Detailed magnetic hysteresis loops measured at different temperature further explore magnetic phase transitions as a function of external field and temperature. A possible phase diagram is similar to the previous Gd/Fe multilayered system in that Mn3O4 is parallel and Fe3O4 antiparallel to the applied field below Tcp while Fe3O4 is parallel and Mn3O4 antiparallel to the applied field above Tcp. Moreover, a spin-flop-like phase is observed above a critical external field, H∗, ∼10 kOe. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Fabrication of a Josephson junction using an atomic force microscope

Insang Song, Byong Man Kim, and Gwangseo Park

Appl. Phys. Lett. 76, 601 (2000); http://dx.doi.org/10.1063/1.125830 (3 pages) | Cited 15 times

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A Josephson junction was fabricated by inducing a selective surface modification on a YBa2Cu3O7−y strip with an atomic force microscope (AFM). The surface modification in the field of conductive AFM tip results in the controlled growth of protrusions across the entire strip. By properly regulating the extent of AFM modification, we achieved a Josephson junction. The self-radiation power of about 50 pW at a resonant frequency of 22 GHz was detected from this junction, which is in excellent agreement with the Josephson frequency-voltage relationship. © 2000 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
07.79.Lh Atomic force microscopes
74.72.-h Cuprate superconductors
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
74.25.N- Response to electromagnetic fields

Analyzing the polarization distribution in poled polymer films by scanning Kelvin microscopy

Robert Blum, Andrei Ivankov, Stefan Schwantes, and Manfred Eich

Appl. Phys. Lett. 76, 604 (2000); http://dx.doi.org/10.1063/1.125831 (3 pages) | Cited 2 times

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We present a method for analyzing the homogeneity of the χ(2) distribution in poled nonlinear optical polymer films. The second-order nonlinear coefficient in these polymers is commonly induced by electric-field poling methods which can lead to a χ(2) distribution with poor spatial homogeneity. In this letter, we analyze the χ(2) distribution using scanning Kelvin microscopy. This allows us to detect the height and the direction of the induced polarization through the probing of the countercharges that are present on the polymer surface. We compare the response to that obtained from the scanning second-harmonic microscopy method, in which the direction of the orientation, and thus the phase of χ(2), cannot be seen. © 2000 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
77.22.Ej Polarization and depolarization
77.84.Jd Polymers; organic compounds
42.65.An Optical susceptibility, hyperpolarizability
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.25.+i Surface conductivity and carrier phenomena

Pinhole analysis in magnetic tunnel junctions

R. Schad, D. Allen, Giovanni Zangari, Iulica Zana, D. Yang, Mark Tondra, and Dexin Wang

Appl. Phys. Lett. 76, 607 (2000); http://dx.doi.org/10.1063/1.125832 (3 pages) | Cited 16 times

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Pinholes in the insulating layer of magnetic tunnel junctions are local shortcuts and cause malfunction of such devices. The need for reduction of the tunnel resistance by reduction of the insulator thickness will make this problem even more severe. Therefore, the development of low-resistance magnetic tunnel junctions requires analyzing the pinhole density. We developed a method for pinhole imaging using electrodeposition of copper. Selective nucleation at pinholes produces characteristic structures that can be visualized by conventional microscopy techniques. The experimental conditions were carefully chosen in order to avoid uncontrolled damage of the insulator layer. © 2000 American Institute of Physics.
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75.45.+j Macroscopic quantum phenomena in magnetic systems
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.35.Dv Composition, segregation; defects and impurities
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Pq Electrodeposition, electroplating
75.50.Bb Fe and its alloys

Spin-tunnel-junction thermal stability and interface interdiffusion above 300 °C

S. Cardoso, P. P. Freitas, C. de Jesus, P. Wei, and J. C. Soares

Appl. Phys. Lett. 76, 610 (2000); http://dx.doi.org/10.1063/1.125833 (3 pages) | Cited 80 times

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Spin tunnel junctions (CoFe/Al2O3/CoFe/MnIr) were fabricated with tunneling magnetoresistance (TMR) of 39%–41% after anneal at 300 °C, decreasing to 4%–6% after anneal at 410 °C. Junction resistance decreases from (0.8–1.6) to (0.5–0.8) M Ω μm2 during anneal. The pinned-layer moment decreases by 44% after anneal at 435 °C, but the free-layer moment does not change. The current–voltage characteristics change significantly and become asymmetric above 300 °C. Rutherford backscattering analysis (RBS) shows that above 300 °C, strong interdiffusion starts at the CoFe/MnIr interface with Mn moving into CoFe, causing the electrode moment to decrease. Mn eventually reaches the Al2O3/CoFe interface contributing to the TMR decrease. RBS analysis of a separate CoFe/Al2O3/CoFe structure shows only minor structural changes at the CoFe/Al2O3 interfaces after anneal at 435 °C, possibly leading to a second mechanism for the loss of interface polarization and TMR. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.60.Dv Thermal stability; thermal effects
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
75.45.+j Macroscopic quantum phenomena in magnetic systems
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Control of domain structures and magnetotransport properties in patterned ferromagnetic wires

T. Taniyama, I. Nakatani, T. Yakabe, and Y. Yamazaki

Appl. Phys. Lett. 76, 613 (2000); http://dx.doi.org/10.1063/1.125834 (3 pages) | Cited 17 times

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Observations of controlled domain structures in zigzag patterned cobalt wires are demonstrated. Distinct domain structures are accessible by changing the orientation of magnetic field using the zigzag geometry, which provides a prospective potential to design the desired magnetic structures. Utilizing the subtle technique, we further throw light on the issue of magnetoresistance induced by the different domain structures. It is found that a negative contribution to the resistance is due to the spin configuration around the corner of the zigzag wires and shows an anomalous maximum around 100 K. © 2000 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.60.Ch Domain walls and domain structure

Nanoscale magnetostrictive response in a thin film owing to a local magnetic field

R. Berger, F. Krause, A. Dietzel, J. W. Seo, J. Fompeyrine, and J.-P. Locquet

Appl. Phys. Lett. 76, 616 (2000); http://dx.doi.org/10.1063/1.125835 (3 pages) | Cited 1 time

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Scanning probe microscope experiments are presented in which thin magnetostrictive films deposited on top of micrometer-sized magnetic write heads as used in magnetic hard disk drives, are used to visualize their emanating magnetic field. The magnetostrictive expansion owing to magnetic writing fields is discussed, together with the transduction mechanisms that lead to the vertical and lateral contrast observed. Experimental results verify that the techniques described have a lateral resolution in the realm of 100 nm. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.80.+q Magnetomechanical effects, magnetostriction

Microscopic magnetization reversal in perpendicular anisotropy CoCr thin films

Gottfried Wastlbauer, George D. Skidmore, Chris Merton, Jake Schmidt, E. Dan Dahlberg, and Joseph Skorjanec

Appl. Phys. Lett. 76, 619 (2000); http://dx.doi.org/10.1063/1.125837 (3 pages) | Cited 6 times

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Magnetic force microscopy was used to observe the magnetization reversal in a CoCr thin film on a grain/subgrain scale. The combination of high resolution topographic and magnetic images were used to relate microscopic magnetization changes to the microstructure of the sample. Both uniformly and partially magnetized grains and both uniform and partial magnetization reversal were observed. Statistically, the uniform magnetic state was more prevalent. In addition, there was a visualization of the flux closure between grains. © 2000 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
61.72.-y Defects and impurities in crystals; microstructure
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Two-dimensional magnetic switching of micron-size films in magnetic tunnel junctions

A. Anguelouch, B. D. Schrag, Gang Xiao, Yu Lu, P. L. Trouilloud, R. A. Wanner, W. J. Gallagher, and S. S. P. Parkin

Appl. Phys. Lett. 76, 622 (2000); http://dx.doi.org/10.1063/1.125838 (3 pages) | Cited 27 times

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The magnetic switching behavior of micron-size magnetic tunnel junctions has been studied in two-dimensional magnetic fields. By measuring junction resistance, we obtain information about the magnetization state of the free ferromagnetic layer. Magnetic properties of this layer are explored using the Stoner–Wohlfarth rotational model as a starting point. We use geometric parameters of the critical curves to obtain information about interlayer coupling and domain structure effects in the free layer. © 2000 American Institute of Physics.
Show PACS
75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.45.+j Macroscopic quantum phenomena in magnetic systems
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Kw Domain structure (including magnetic bubbles and vortices)
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