Spin waves in exchange spring nanoheterostructured amorphous/nanocrystalline films

We investigate the structural, static, and dynamic magnetic properties of exchange spring (ES) nanoheterostructured, stress-free, optically smooth films of amorphous/nanocrystalline Co-rich cobalt phosphorous (CoP) prepared by electrodeposition technique at room temperature. Static magnetic measurement reveals different hysteresis loop structures of the thin films - evolution from the low coercivity non-ES loop to the staircaseES loop, giving rise to multiple coercivities for relatively higher thickness films. The first-order reversal curve (FORC) distributions demonstrate the different reversal mechanisms present in the samples and confirm the nonES and ES natures of the films. The field-dependent Brillouin light scattering (BLS) spectra of the ES thin film unveil two well-resolved spin wave peaks associated with the bulk modes (B) and the so-called Damon-Eshbach (DE) surface spin wave modes (S) while that for non-ES low coercivity sample show a doublet of modes below a certain value of the applied field. Observation of the S mode only on one side of the measured spectra depends on the direction of the external magnetic field due to the nonreciprocal character of the S wave in the micrometer thickness of the investigated films. The external magnetic field-dependent BLS spectra yield an almost linear dependence of the mode frequencies versus the magnetic field intensity. Studied BLS measurements demonstrate the evolution of the ES structure in 5.7-& mu;m-thick nanohetero-structured CoP film compared to the 1.4-& mu;mthick non-ES sample. Additionally, the increase in the interfacial exchange energy value (JIES - 10.12 erg/cm2) in the 5.7 & mu;m film compared to that (Jnon-ES - 3.68 erg/cm2) of 1.4-& mu;m film (calculated from corresponding asymmetric peak fittings to the measured BLS spectra) reduces the interfacial exchange energy ratio (Jnon-ES below unity, confirming the enhanced strength of the exchange coupling in the developed ES film.

Automated summary

The study investigates the magnetic properties of exchange spring nanoheterostructured CoP films prepared by electrodeposition at room temperature. Static magnetic measurement reveals different hysteresis loop structures, and the first-order reversal curve distributions confirm the nature of the films. Field-dependent Brillouin light scattering spectra unveil different spin wave modes in the films. The study demonstrates the evolution of the exchange spring structure and the enhanced strength of the exchange coupling in the developed film.