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  • 1
    Electronic Resource
    Electronic Resource
    Magnetization reversal in permalloy particles: Micromagnetic computations : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5276-5278 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization distributions in a rectangular permalloy particle with an 8:1 aspect ratio are presented. When a magnetic field is applied along the easy axis of the particle, there is considerable change in the vortex pattern as the applied field varies, but the moment is nearly constant. Magnetization reversal is sudden. When a field is applied oblique to the easy axis the magnetization is rather uniform in most of the particle. When an in-plane field is applied exactly along the hard axis, a complex domain structure is formed, so that the remanence is zero, in agreement with experiment. Formation of this state requires that the applied field exceed a critical value. Upon application of an easy axis field to this complex state, the domain structure is shifted so that the magnetization increases linearly with the applied field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348945
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  • 2
    Electronic Resource
    Electronic Resource
    Hysteresis in lithographic arrays of permalloy particles: Experiment and theory (invited) : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5262-5266 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the effects of particle size and aspect ratio on the hysteresis in controlled arrays of small magnetic particles. The arrays of permalloy particles were fabricated via electron-beam lithography. Each array consists of ∼ 106 identical, uniformly spaced particles. Hysteresis loops measured with an alternating-gradient magnetometer for particles ∼5–0.1 μm are presented. We find an increase in the coercive force as the particle width decreases below 0.3 μm due to a change in the switching mechanism from domain-wall nucleation and wall motion to vortex nucleation and vortex motion. A novel angular dependence of the loops is described in detail. Results from ab initio micromagnetic calculations on isolated rectangular Permalloy particles are compared, where applicable, with the measurements. We find excellent qualitative and, in selected cases, quantitative agreement between the experiments and calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348071
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  • 3
    Electronic Resource
    Electronic Resource
    Modeling the behavior of the magnetic force microscope : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5877-5879 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of some numerical simulations are presented that model the behavior of the magnetic force microscope under various probe/sample configurations. Analysis is carried out under the assumption of uniform magnetization of an axially symmetric probe of various types including: sphere, cylinder, conical tip, and rounded magnetically coated conical tip. In these cases the analysis can be made by studying the effective magnetic surface charge on the probe. We also consider the case of a spherical probe with magnetization that can rotate in response to the local field. The sample configurations studied are also of the axially symmetric type, which can be used to model the fields generated by arrays of cylindrical samples, e.g., alumite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347854
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic force microscope study of the micromagnetics of submicrometer magnetic particles (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 4516-4521 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A high-resolution, high-sensitivity magnetic force microscope (MFM) with the ability to image in an in situ magnetic field is described. This MFM has been used to investigate the micromagnetics of nanolithographically produced magnetic particles. It is shown that the particles' switching fields can be determined without being perturbed by the stray fields from the sensing tip. This allows the study of the evolution of the particles' magnetic states as a function of applied field and the direct observation of cooperative switching among interacting particles. The switching fields of individual particles are compared with remanent magnetization data, taken with an alternating gradient magnetometer, on both isolated and interactive arrays of particles. A method is described for estimating the strength of the interaction between particles by comparing the switching fields of different configurations of particle moments created by using the MFM tip as a local field source. Finally, a novel remanent magnetization state has been observed which provides a check on the validity of micromagnetic numerical simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352794
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of an unusual ESR signal in antiferromagnetic Eu2CuO4 : 35th annual conference on magnetism and magnetic materials (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 4872-4873 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of an unusual electron spin resonance (ESR) signal in single crystals of Eu2CuO4. The signal appears to be associated with a resonance mode of the CuO2 planes, similar to the midfield and low-field absorptions we have reported previously [Phys. Rev. B 41, 1934 (1990)]. However, it is only observed when the projection of the applied dc magnetic field in the CuO2 plane is within a few degrees of the 〈110〉 crystallographic direction. Additionally the sample must be field cooled in the CuO2 plane, but with a component of the cooling field perpendicular to the 〈110〉 ESR observation direction. Both the field for resonance and the linewidth exhibit a 1/cos θ dependence, where θ is the angle of the applied dc field between the c axis and the 〈110〉 observation direction. Additional constraints for observation of the resonance are that the microwave rf magnetic field must have a component in the CuO2 plane, but perpendicular to the dc field. The signal disappears above ∼215 K, which we assume is associated with the antiferromagnetic ordering temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348208
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  • 6
    Electronic Resource
    Electronic Resource
    A high-sensitivity alternating-gradient magnetometer for use in quantifying magnetic force microscopy : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5880-5882 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An extremely sensitive alternating gradient magnetometer (AGM) has been developed. This AGM has been designed as an aid in characterizing the response of magnetic force microscope tips to known magnetic fields and field gradients. It should also prove useful as a general purpose magnetometer for small samples. A sensitivity of ∼ 1.4 × 10−11 emu has been achieved. Minor improvements in vibration isolation should bring this number down to ∼ 10−12 emu. A sensitivity of ∼ 10−14 emu is theoretically possible. The capabilities of the AGM are illustrated with magnetization versus field data for an 8-μm Ni sphere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347855
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  • 7
    Electronic Resource
    Electronic Resource
    Noise analysis and image focusing for magnetic force microscopy : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5805-5807 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic force microscopy (MFM) has been widely utilized to reveal magnetization distributions by sensing the external magnetic-field distribution very close to the sample. The resolution of MFM is determined by the size of the sensor tip and by the spacing between the tip and the measured sample. A technique is developed to analyze the noise and linearity of a MFM image, and consequently to improve the spatial resolution by reducing the spacing loss. As a demonstration, a series of MFM images of a single permalloy particle is obtained and numerically analyzed. The spacing loss is reduced and a much higher resolution image is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353583
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  • 8
    Electronic Resource
    Electronic Resource
    Observation of thermal switching of a single ferromagnetic particle : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6961-6963 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A magnetic force microscope (MFM) has been shown to be able to detect fields emanating from submicrometer permalloy particles with magnetic moments as low as 10−13 emu. We have used this MFM equiped with an in situ electromagnet to study the angular dependence of the switching field Hs(θ), and the probability of thermal switching of a single-domain permalloy particle as a function of the time duration of an applied magnetic field H. The angular dependence of Hs(θ) is significantly different from that expected for coherent rotation. For applied magnetic fields close to Hs, the time dependence of the probability for not switching cannot be fit with a simple exponential. These data indicate that multiple-energy barriers of similar height are involved in the thermally activated process responsible for the reversal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.352397
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  • 9
    Electronic Resource
    Electronic Resource
    Apparatus for in situ measurement of surface magnetic moments prepared in UHV (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 484-488 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An apparatus for making in situ measurements of the magnetic moment of submonolayer through multimonolayer samples deposited in a UHV chamber is described. The UHV chamber is designed to be used with a commercial SQUID magnetometer with a sensitivity of ∼10−8 emu. The component of magnetic moment parallel to the sample surface may be measured over the temperature range 4–400 K and for magnetic fields (applied parallel to the surface) up to 5 T. A thin re-entrant metal tape is used both as an initial substrate for the deposition of any desired films, and as the means of transporting the deposited sample from the evaporation and evaluation regions of the vacuum chamber to the SQUID analysis region. Some results for Fe evaporated on polycrystalline Ag films are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142092
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  • 10
    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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