Switching field and thermal stability of CoPt/Ru dot arrays with various thicknesses

The switching fields and thermal stability of CoPt/Ru dot arrays with various dot thickness delta (5-20 nm) were experimentally investigated as a function of the dot diameter, D, (130-300 nm). All dot arrays showed a single domain state, even after removal of an applied field equal to the remanence coercivity Hr. The angular dependence of Hr for the dot arrays indicated coherent rotation of the magnetization during nucleation. We estimated the values of the "intrinsic" remanence coercivity H0 obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation E0/(kBT). The variation in H0 as a function of delta and D was qualitatively in good agreement with that of the effective anisotropy field at the dot center Hk eff(r=0), calculated taking account of the demagnetizing field in the dots. The ratio of H 0 to Hk eff(r=0) for the dot arrays with delta=10 nm increased from 0.53 to 0.70 as D decreased from 300 to 140 nm, and no significant difference in the H0/Hk eff(r=0) ratio due to the difference in delta was observed. On the other hand, E0/(k BT) decreased as delta decreased. E0/(kBT) increased slightly as D decreased, but, was not so sensitive to D over the present D rang

Microwave Spectroscopy of a Single Permalloy Chiral Metamolecule on a Coplanar Waveguide

We investigate the microwave spectroscopies of a micrometer-sized single permalloy (Py) chiral structure on coplanar waveguides (CPWs). Under an external dc magnetic field applied in a direction perpendicular to the microwave propagation, the Py chiral structure loaded on the center of the CPW signal line shows Kittel-mode ferromagnetic resonance. Contrastingly, the structure on the signal-line edge highlights two additional resonances: spin-wave resonance at a higher frequency, and unique resonance at a lower frequency of approximately 7.8 GHz. The resonance signal at 7.8 GHz originates from magnetically induced, geometry-driven resonance, although the resonance frequency does not depend on the external magnetic field. Moreover, the displacement of the Py structures on the signal line results in nonreciprocal microwave transmission, which is traced back to the edge-guide mode