Browsing by Author "Lograsso, Thomas A."

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    Fe-Ga/Pb(Mg1/3Nb2/3)O-3-PbTiO3 magnetoelectric laminate composites
    Dong, Shuxiang; Zhai, Junyi; Wang, Naigang; Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Lograsso, Thomas A. (AIP Publishing, 2005-11-01)
    We have found large magnetoelectric (ME) effects in long-type laminate composites of Fe-20% Ga magnetostrictive alloys and piezoelectric Pb(Mg1/3Nb2/3)O-3-PbTiO3 single crystals. At lower frequencies, the ME voltage coefficient of a laminate with longitudinally magnetized and longitudinally polarized (i.e., L-L mode) layers was 1.41 V/Oe (or 1.01 V/cm Oe). Near the natural resonant frequency (similar to 91 kHz) of the laminate, the ME voltage coefficients were found to be dramatically increased to 50.7 V/Oe (36.2 V/cm Oe) for the L-L mode. In addition, the laminate can detect a minute magnetic field as low as similar to 2 x 10(-12) T at resonance frequency, and similar to 1 x 10(-10) T at lower frequencies. (c) 2005 American Institute of Physics.
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    Magnetic force microscopy investigation of domain structures in Fe-x at. % Ga single crystals (12 < x < 25)
    Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Wu, D.; Lograsso, Thomas A. (American Institute of Physics, 2005-07-15)
    The domain structure of furnace-cooled (FC) and post-annealed (PA) Fe-x at. % Ga (x=12, 20, and 25) crystals has been investigated by magnetic force microscopy. For both FC and PA Fe-12 at. % Ga, the domains were found to be well-aligned and oriented along the [100] direction. For Fe-20 at. % Ga, although a preferred [100] orientation remained, a difference in morphology was found between FC and PA conditions-in the PA condition, clear dendritic domains were observed. For both FC and PA Fe-25 at. % Ga, a much reduced [100] preferred domain orientation was found, the domain size was notably reduced, and dendrite formation was not observed. (c) 2005 American Institute of Physics.
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    Magnetostrictive and magnetoelectric behavior of Fe-20 at. % Ga/Pb(Zr,Ti)O-3 laminates
    Dong, Shuxiang; Zhai, Junyi; Bai, Feiming; Li, Jiefang; Viehland, Dwight D.; Lograsso, Thomas A. (American Institute of Physics, 2005-05-15)
    The magnetostrictive and magnetoelectric (ME) properties of laminate composites of Fe-20 at. % Ga and Pb(Zr,Ti)O-3 (PZT) have been studied for laminates of different geometries. The results show that (i) a long-type magnetostrictive Fe-20 at. % Ga crystal plate oriented along (001), and magnetized in its longitudinal (or length) direction has higher magnetostriction than a disk-type one; and consequently (ii) a long-type Fe-20 at. % Ga/PZT laminate has a giant ME effect, and is sensitive to low-level magnetic fields. (c) 2005 American Institute of Physics.
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    Origin of magnetic and magnetoelastic tweedlike precursor modulations in ferroic materials
    Saxena, A.; Castan, T.; Planes, A.; Porta, Micaela; Kishi, Y.; Lograsso, Thomas A.; Viehland, Dwight D.; Wuttig, Manfred; De Graef, M. (American Physical Society, 2004-05-14)
    Based on experimental observations of modulated magnetic patterns in a Co(0.5)Ni(0.205)Ga(0.295) alloy, we propose a model to describe a ( purely) magnetic tweed and a magnetoelastic tweed. The former arises above the Curie (or Neel) temperature due to magnetic disorder. The latter results from compositional fluctuations coupling to strain and then to magnetism through the magnetoelastic interaction above the structural transition temperature. We discuss the origin of purely magnetic and magnetoelastic precursor modulations and their experimental thermodynamic signatures.
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    Structural studies of Fe0.81Ga0.19 by reciprocal space mapping
    Viehland, Dwight D.; Li, Jiefang; Lograsso, Thomas A.; Ross, A.; Wuttig, Manfred (AIP Publishing, 2002-10-01)
    Reciprocal lattice mapping has been performed on Fe0.81Ga0.19 crystals by omega-omega/2theta, Psi-phi, and omega-phi scans. A strong elongation of the <001>(c) peak was found along the <110>(c) direction. omega scans revealed short lateral correlation lengths xi along <110>(c) and strong diffuse scattering along the <001>(c). Multiple domains with monoclinic symmetry (angle similar to190degrees) were observed by Psi-phi and omega-phi scans on the (001)(c) face, and were also tilted with respect to each other. The results show an average cubic structure with orthorhombic structural modulations, and two structural domain states that result in a limiting monoclinic symmetry. (C) 2002 American Institute of Physics.