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20 Apr 1998

Volume 72, Issue 16, pp. 1939-2058

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Magnetoresistance of artificial La0.7Sr0.3MnO3 grain boundaries as a function of misorientation angle

S. P. Isaac, N. D. Mathur, J. E. Evetts, and M. G. Blamire

Appl. Phys. Lett. 72, 2038 (1998); http://dx.doi.org/10.1063/1.121257 (3 pages) | Cited 67 times

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The resistance of polycrystalline doped LaMnO3 materials has been shown to be highly sensitive to low magnetic fields. To enable direct study of the properties of isolated grain boundaries we have grown epitaxial La0.7Sr0.3MnO3 films on a series of bicrystal substrates with different misorientation angles and patterned the films into a Wheatstone bridge geometry. We show that the grain boundary resistance and its magnetic field dependence vary strongly with the misorientation angle. The temperature dependence of the grain boundary resistance is also presented. We have obtained resistance changes of over 3% in fields of 2 mT at 300 K. © 1998 American Institute of Physics.
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73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
75.47.De Giant magnetoresistance

Phase transitions in planar magnetic nanostructures

R. P. Cowburn and M. E. Welland

Appl. Phys. Lett. 72, 2041 (1998); http://dx.doi.org/10.1063/1.121258 (3 pages) | Cited 60 times

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Using numerical micromagnetics we have studied the ground state magnetization distribution of square planar ferromagnetic elements (“nanostructures”). As the element size is reduced from 250 to 2 nm at constant thickness (2–35 nm), we find that the magnetization distribution undergoes up to three phase transitions involving as many as three different near single domain states. One of these phase transitions is analogous to the reorientation phase transition observed in continuous ultrathin magnetic films. © 1998 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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.)
75.60.Ch Domain walls and domain structure

Magnetoelastic properties of epitaxial holmium and erbium thin films

M. Ciria, J. I. Arnaudas, A. del Moral, M. R. Wells, and R. C. C. Ward

Appl. Phys. Lett. 72, 2044 (1998); http://dx.doi.org/10.1063/1.121259 (3 pages) | Cited 4 times

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The magnetoelastic (MEL) stresses of single crystal Ho and Er thin films are measured at low temperatures and in applied magnetic fields up to 12 T by means of a capacitive cantilever technique, to determine the irreducible second-order basal plane MEL stress Bγ,2. For Ho, the data are well fit by the Callen and Callen law, giving Bγ,2=0.29 GPa at 0 K and 12 T, slightly larger than the bulk value, which suggest a negligible effect of the clamping on Bγ,2. For Er, the lack of saturation prevents the determination of the single-ion contribution to Bγ,2 at 0 K. Nevertheless, its sign, which is negative, agrees with the theoretical crystal field prediction. © 1998 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction

Mössbauer and magnetic study of substituted magnetites

M. Sorescu, D. Mihaila-Tarabasanu, and L. Diamandescu

Appl. Phys. Lett. 72, 2047 (1998); http://dx.doi.org/10.1063/1.121260 (3 pages) | Cited 20 times

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Co, Ni, Mn, Cr, and Cu substituted magnetites were prepared by the hydrothermal method at 300 °C, with concentrations ranging from 8.2% to 12.5%. Transmission electron microscopy determined the average particle diameter 〈Φ〉 to be in the hundred of nm range and the morphological modifications induced by the various substitutions employed. Hysteresis loop measurements were performed to determine the coercive field Hc, and saturation magnetic moment ms. While Hc decreased with increasing 〈Φ〉, the particle shape was found to play an important role in explaining the dependence of ms on 〈Φ〉. Transmission Mössbauer spectroscopy was used to determine the site preference of the substitutions and their effect on the hyperfine magnetic fields. The room-temperature Mössbauer spectra were analyzed assuming a random distribution of substitutents using the binomial distribution from the ionic crystal point of view. Superparamagnetic particles were observed at room temperature in the case of Cu and Cr substituted magnetites. © 1998 American Institute of Physics.
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75.30.Hx Magnetic impurity interactions
75.50.Tt Fine-particle systems; nanocrystalline materials
76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials

Spin dependent electron absorption in Fe(001)-p(1×1)O: A new candidate for a stable and efficient electron polarization analyzer

Riccardo Bertacco, Michele Merano, and Franco Ciccacci

Appl. Phys. Lett. 72, 2050 (1998); http://dx.doi.org/10.1063/1.121261 (3 pages) | Cited 30 times

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The low energy electron absorption by a p(1×1) ordered oxygen overlayer on magnetized Fe(001) depends on the spin polarization of the primary beam. The peak value of the spin asymmetry is 12.5% at 6 eV electron kinetic energy, where the percentage absorption is 65%. The presence of the surface oxide prevents the system from contamination, so that an almost negligible asymmetry deterioration is observed after prolonged operation in vacuum. After exposure to atmosphere followed by heat-cleaning a peak value still larger than 7% is achieved. These results suggest spin dependent current absorption from Fe(001)-p(1×1)O as a very promising candidate for an efficient and extremely stable electron polarization analyzer. © 1998 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
07.60.Fs Polarimeters and ellipsometers
61.80.Fe Electron and positron radiation effects
81.65.Mq Oxidation

Effect of magnetic field on the superparamagnetic relaxation in granular Co-Ag samples

Y. D. Zhang, J. I. Budnick, W. A. Hines, C. L. Chien, and J. Q. Xiao

Appl. Phys. Lett. 72, 2053 (1998); http://dx.doi.org/10.1063/1.121262 (3 pages) | Cited 22 times

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In order to study the effect of applied magnetic field on the superparamagnetic relaxation behavior of small Co particles, magnetization measurements were carried out on as-prepared and annealed granular samples of Co20Ag80 and Co25Ag75. Values of the superparamagnetic blocking temperature TB− were obtained from the characteristic peak in the zero-field-cooled magnetization. Consistent with existing models, it was found that the initial decrease of TB− with applied magnetic field is quadratic. An estimate of the magnetic anisotropy “energy density” Ku yielded a value which is two orders of magnitude greater than the value for bulk cobalt. The results reported here underscore the importance of considering the effect of superparamagnetic relaxation on the performance of nanostructured magnetic materials. © 1998 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.50.Kj Amorphous and quasicrystalline magnetic materials
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