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  • 1
    Electronic Resource
    Electronic Resource
    Thermal relaxation of the pinned layer magnetization in NiO spin valves (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5036-5038 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A variation of the switching field of the pinned layer (PL) magnetization in NiO based spin valves was observed as a function of the rate of variation of the applied field. This phenomenon was characterized at low frequencies (0.4–120 Hz) using quasistatic magnetoresistance (MR) transfer curve testing and measurements of the relaxation of the resistance around the quasistatic switching field of the pinned layer (10−1–105 s). The influence of temperature was investigated between room temperature and 125 °C. The relaxation data were fit using a model based on an Arrhenius law thermal activation with a single relaxation time. The variation in the switching field of the pinned layer as a function of the applied field rate was compared to the Kurkijärvi model. The fit parameters in both models are the energy barrier height and the thermally activated volume of nucleation. The parameters derived from both types of experiments agree remarkably well. The understanding of this low frequency magnetic behavior of spin valves allows one to gain insight into the long-term relaxation of the magnetization of the PL in MR readback heads, as well as into the magnetic response of this layer to very short (ns) pulses of field or high frequency (100 MHz) excitations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370083
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  • 2
    Electronic Resource
    Electronic Resource
    Preparation and quantitative magnetic studies of single-domain nickel cylinders : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5303-5305 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a complete experimental and theoretical explanation of the magnetic processes in an interacting collection of submicron magnetic particles, a fundamental understanding of the magnetic properties of individual single-domain particles must first be achieved. We have prepared elongated Ni columns ranging in diameter from 0.15 to 1.0 μm by electroplating into specially prepared Al2O3 and glass channeled pore membranes. We have also prepared controlled arrays of Ni columns using e-beam lithography, subsequently electroplating into the written patterns. Using transmission electron microscopy, we have characterized the shape, size, morphology, and crystal structure of the columns. Magnetic force microscopy has been used to determine the switching field Hs versus the applied field angle of the columns. Although the switching field data can be fit to the functional form for nucleation by curling in an infinite cylinder, the observed weak dependence of Hs on column diameter is inconsistent with that expected for curling, particularly for columns of diameter (approximately-greater-than)0.3 μm. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361359
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  • 3
    Electronic Resource
    Electronic Resource
    A scanning microscope using a magnetoresistive head as the sensing element : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6067-6069 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have built a scanning probe microscope where a magnetoresistive (MR) head is used as the sensing element. The sensor region of the MR head is about 5 μm wide and 30 nm thick giving high resolution in one direction and poor resolution in the other. As MR heads with smaller cross-track dimensions are developed, submicron resolution in this direction should also be realizable. The MR head is mounted on a piezoelectric bimorph and vibrated perpendicular to the plane of the sample, and the ac voltage output of the head is detected with a lock-in amplifier. We have imaged pre-recorded bits as a function of scan height, and also imaged bits that were written using the write element of the same MR head. The typical voltage change through a transition is ∼4 μV, two orders of magnitude smaller than signals generated on a spin stand. This is most likely due to the difficulty in setting the slider parallel to within submilliradian accuracy to the plane of the sample. Our positioning system does not have this capability at this time. With modifications in the positioning stage, this device should provide a valuable tool for investigating the recording and playback processes, and for characterizing media and heads at ever decreasing track widths, bit separations, and flying heights. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362094
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  • 4
    Electronic Resource
    Electronic Resource
    Investigation of the magnetization reversal mode for individual ellipsoidal single-domain particles of γ-Fe2O3 (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7989-7992 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report measurements of the angular dependence of the switching field of individual ellipsoidal single-domain ferromagnetic particles. The measurements were carried out by Lorentz magnetometry on submicrometer γ-Fe2O3 particles and provide insights into the magnetization reversal for individual ellipsoidal particles of known morphology. The functional form of the switching field data indicates that the particles reverse by curling over a narrow range near 0 degrees and by coherent rotation at all larger angles. A value of 3±2×10−7 erg/cm for the exchange constant of the γ-Fe2O3 is obtained from these measurements. We suggest that the long desired goal of complete characterization of the magnetic properties of individual single-domain particles is now feasible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356535
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  • 5
    Electronic Resource
    Electronic Resource
    Switching field studies of individual single domain Ni columns : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 5458-5460 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Quantitative measurements of the switching field properties of individual single-domain particles are both scientifically and technologically important. Such data are relevant for the engineering of a patterned magnetic storage medium where a single bit of information corresponds to individual single-domain particles with sizes consistent with storage densities 〉50 Gbit/in2. By electroplating into Al2O3 and track-etched polycarbonate filters, we have prepared particles over a large range of radii from R=20–500 nm, and have characterized them by transmission electron microscopy. Using a magnetic force microscope with an in situ electromagnet, we have quantified the extent to which the particles can be considered "single-domain." We have also measured the angular dependence of the switching field Hs for these particles. At zero degrees, Hs lies above the curling curve for R/R0〉4, and falls below the curling curve for R/R0〈2, where R0 is the exchange length (R0=20.6 nm for Ni). At intermediate radii, the angular dependence data are close to the curling curve with a crossover of the data and the curling solution at R/R0∼3. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364569
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  • 6
    Electronic Resource
    Electronic Resource
    Measurement of thermal switching of the magnetization of single domain particles (invited) : 38th Annual Conference on Magnetism and Magnetic Materials (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 6217-6222 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an experimental study of the thermally activated switching of the magnetization of individual isolated γ-Fe2O3 particles. These particles are prolate ellipsoids ∼3000 A(ring) long and 650 A(ring) wide. The measured angular dependence of the switching field, Hs(θ), is consistent at large angles with a uniform rotation, but as θ approaches zero, other modes of reversal appear possible, and most likely the mode of reversal is curling. By measuring the probability of reversal of the moment as a function of time and applied magnetic field at T∼300 K, we found that the switching was thermally assisted, but couldn't be described by hopping over a single energy barrier. Our results indicate that the dynamics of switching are described by a complex path in the energy landscape.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355404
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  • 7
    Electronic Resource
    Electronic Resource
    Fabrication and characterization of nanoscale arrays of nickel columns : The 41st annual conference on magnetism and magnetic materials (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 4730-4732 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated arrays of high aspect ratio nickel columns in both PMMA and SiO2, and we have characterized their structure using transmission electron microscopy and scanning electron microscopy. We have also characterized the magnetics of the columns with magnetic force microscopy. Such characterization of high aspect ratio perpendicular magnetic particles is only rarely found in the literature. This work lays a foundation for further studies to test the viability of lithographically defined arrays of magnetic particles as an alternative high density storage medium. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365444
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