A local magnetoresistance ͑MR͒ effect associated with the switching of a coherent spin block confined in a cross-shaped junction of mesoscopic ferromagnetic NiFe wires was probed with the voltage pads attached close ͑Ͻ1.5 m͒ to the junction. A positive intrinsic MR effect, i.e., an increase in resistance, associated with local spin noncollinearity, or a 45°domain wall, in a 0.5 m cross was demonstrated while the anisotropic MR and the Lorentz MR were unambiguously excluded.
The scaling of the magnetic hysteresis loop area of permalloy disks (20–400 μm diam) has been studied as a function of applied field amplitude H0 and frequency Ω using scanning Kerr microscopy. An increase in the dynamic coercivity with reduced size is observed for d<100 μm in the frequency range studied (0.1–800 Hz). However, the loop area A follows the scaling relation A∝H0αΩβ, with α≈0.14 and β≈0.50 throughout the entire size range studied. Our results demonstrate that the dynamic scaling behavior is universal even though the lateral size influences the domain structure and magnetic reversal behavior.
The magnetization reversal and magnetic anisotropy in Co network structures have been studied using magneto-optic Kerr effect (MOKE). An enhancement of the coercivity is observed in the network structures and is attributed to the pinning of domain walls by the hole edges in the vicinity of which the demagnetizing field spatially varies. We find that the magnetization reversal process is dominated by the intrinsic unaxial anisotropy (2K(u)/M(s)approximate to 200 Oe) in spite of the shape anisotropy induced by the hole edges. The influence of the cross-junction on the competition between the intrinsic uniaxial anisotropy and the induced shape anisotropy is discussed using micromagnetic simulations
Permalloy (Ni80Fe20) squares (30 nm thick and w mu m wide; 1 less than or equal to w less than or equal to 200 mu m) and circular disks (30 nm thick and r mu m diameter; 1 less than or equal to r less than or equal to 200 mu m) prepared on a GaAs (100) substrate were observed in both their demagnetized and remanent states by magnetic force microscopy (MFM) associated with non-contact atomic force microscopy (NC-AFM). The squares (2 less than or equal to w mu m) exhibited conventional closure domains and the corner plays a very important role in creating new walls. The circular disks, on the other hand, formed either vortex domain (5 less than or equal to r less than or equal to 20 mu m) or multi-domain (50 less than or equal to r mu m) states, The magnetization rotation is observed by MFM to change according to the size and shape of the elements, The MFM observations are supported by micromagnetic calculations which confirm the effect of the corner on the domain wall formation
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