A combined experimental and computational study of Ni₃Pt/Ir/Co synthetic ferrimagnets : taking atomistic spin simulation into the laboratory

• Main Author: Scott, Jade
• Format: Dissertation
• Language: English
• Published: Queen's University Belfast 2020

Synthetic ferrimagnets, two ferromagnetic layers exchange coupled antiferromagnetically through a non-magnetic spacer layer, provide an interesting test bed for future all optical magnetic switching and to validate, in an experimental and engineering context, the utility of atomistic spin modelling of technological structures. In this thesis, this is achieved through the integration of experiment and modelling in the study of a series of Ni₃Pt/Ir/Co synthetic ferrimagnets, fabricated via magnetron sputtering, characterised experimentally using both bulk and element specific magnetometry and through application of the atomistic spin simulation package, VAMPIRE. Design and fabrication of synthetic ferrimagnet structures requires knowledge and control of the temperature-dependent magnetisation, M(T) and anisotropy K(T) of each layer and the exchange coupling between them. Unexpectedly, these Ni₃Pt/Ir/Co synthetic ferrimagnets exhibit two points of zero remanent magnetisation, one at the expected magnetisation compensation point, Tcomp, where the moments of each layer are equal, and another at lower temperatures, T-MR, where the moments of the Ni₃Pt and Co are unequal and the zero point arises from an interplay of the anisotropy, Zeeman and exchange energies in the system. Between these two temperatures, the Ni₃Pt/Ir/Co synthetic ferrimagnets exhibit negative remanence where the layer with higher moment reverses against the applied field. This unusual behaviour only arises due to a very delicate balance of the anisotropy, Zeeman and exchange energies and therefore provides an ideal environment with which to probe the practicality of VAMPIRE as a lab tool and to investigate its effectiveness applied to a real experimental system.