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7 Aug 2000

Volume 77, Issue 6, pp. 767-915

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Temporal evolution of spin-polarization in ferromagnetic tunnel junctions

D. J. Monsma and S. S. P. Parkin

Appl. Phys. Lett. 77, 883 (2000); http://dx.doi.org/10.1063/1.1306641 (3 pages) | Cited 16 times

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The spin polarization of the simple transition-metal ferromagnets Fe, Co, and Ni can be measured using ferromagnet/insulator/superconductor tunneling structures. Measurements, carried out over the past 20 years using superconducting aluminum electrodes and alumina tunneling barriers, have given a wide range of values, especially for Ni. In this letter, we show that high-spin-polarization values are found for Ni using superconducting films formed from Cu-doped aluminum deposited in a high-vacuum sputter-deposition system. However, we find that the magnitude of the spin polarization slowly decreases over time, which we believe to result from a reaction between Ni and alumina. We conclude that the spin-polarization values measured in such studies are strongly influenced by the detailed structure of the ferromagnet–superconductor interface. © 2000 American Institute of Physics.
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75.50.Cc Other ferromagnetic metals and alloys
68.35.Ct Interface structure and roughness
74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

6% magnetic-field-induced strain by twin-boundary motion in ferromagnetic Ni–Mn–Ga

S. J. Murray, M. Marioni, S. M. Allen, R. C. O’Handley, and T. A. Lograsso

Appl. Phys. Lett. 77, 886 (2000); http://dx.doi.org/10.1063/1.1306635 (3 pages) | Cited 395 times

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Field-induced strains of 6% are reported in ferromagnetic Ni–Mn–Ga martensites at room temperature. The strains are the result of twin boundary motion driven largely by the Zeeman energy difference across the twin boundary. The strain measured parallel to the applied magnetic field is negative in the sample/field geometry used here. The strain saturates in fields of order 400 kA/m and is blocked by a compressive stress of order 2 MPa applied orthogonal to the magnetic field. The strain versus field curves exhibit appreciable hysteresis associated with the motion of the twin boundaries. A simple model accounts quantitatively for the dependence of strain on magnetic field and external stress using as input parameters only measured quantities. © 2000 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Cc Other ferromagnetic metals and alloys
61.72.Mm Grain and twin boundaries
81.40.Jj Elasticity and anelasticity, stress-strain relations

Reduced coercivity in ferromagnetic Co–Cu coevaporated epitaxial films on Cu(111)

J. E. Prieto, J. Camarero, J. J. de Miguel, R. Miranda, Ch. Rath, S. Müller, L. Hammer, and K. Heinz

Appl. Phys. Lett. 77, 889 (2000); http://dx.doi.org/10.1063/1.1306650 (3 pages) | Cited 3 times

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Epitaxial films grown by coevaporation of Co and Cu on Cu(111) were investigated by low-energy electron diffraction and surface magneto-optical Kerr-effect measurements. The films are dominantly face-centered-cubic stacked up to high Co concentrations and exhibit ferromagnetism. Their coercivity is significantly reduced compared to pure Co films produced by thermal Co deposition on Cu(111) independent of the use of Pb as a surfactant. © 2000 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Layer selective determination of magnetization vector configurations in an epitaxial double spin valve structure: Si(001)/Cu/Co/Cu/FeNi/Cu/Co/Cu

B. C. Choi, A. Samad, C. A. F. Vaz, J. A. C. Bland, S. Langridge, and J. Penfold

Appl. Phys. Lett. 77, 892 (2000); http://dx.doi.org/10.1063/1.1306395 (3 pages) | Cited 3 times

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The magnetization vector configurations in an epitaxial Si(001)/Cu/Co/Cu/Fe20Ni80/Cu/Co/Cu double spin valve structure have been investigated at room temperature using polarized neutron reflectivity measurements. The layer-averaged magnetic moment per FeNi atom was found to be 0.99±0.06 μB at saturation, while the top (bottom) Co layer moment was 1.69±0.09 μB (1.67±0.08 μB), which are identical to the bulk values within experimental error. Furthermore, the Co magnetization vectors are found to lie in-plane but canted with respect to the applied field direction for an applied field strength smaller than the coercive fields (∼80 and 130 Oe) of the Co layers. This result indicates that a complete antiparallel alignment of the layer magnetizations is not reached causing a corresponding reduction in the giant magnetoresistance (GMR). These observations emphasize the importance of the detailed spin configuration in determining the GMR amplitude at low fields. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.15.Gd Galvanomagnetic and other magnetotransport effects
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.)
75.30.Cr Saturation moments and magnetic susceptibilities

SmNi4B: A narrow domain-wall ferromagnet

Chandan Mazumdar, R. Nagarajan, L. C. Gupta, B. D. Padalia, and R. Vijayaraghavan

Appl. Phys. Lett. 77, 895 (2000); http://dx.doi.org/10.1063/1.1306294 (3 pages) | Cited 19 times

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We have investigated magnetic properties of SmNi4B. The material undergoes a ferromagnetic ordering at TC ≈ 39 K, which, surprisingly, is higher than that of isostructural GdNi4B ( ≈ 36 K). The saturation magnetic moment is rather small (0.15 μB per Sm at 5 K), suggesting the presence of crystal-field effects. Below TC, the material exhibits a large thermomagnetic irreversibility and also a large magnetic hysteresis at 5 K with a coercive field ≈ 28 kOe, which is one of the largest observed in a Sm-based material. We suggest that the large coercive field is intrinsic, associated with narrow domain walls of thickness of only one atomic layer, which resembles a ferroelectric wall. © 2000 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.70.Ch Crystal and ligand fields
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