Temperature and strain dependence of the magnetic properties of multilayers with interfacial DMI

Magnetic multilayers with perpendicular anisotropy and an interfacial Dzyaloshinskii-Moriya interaction contain chiral domain walls and skyrmions that are promising for applications. Here we measure the temperature dependence of the Dzyaloshinskii-Moriya interaction (DMI) in Pt/CoFeB/Ir and Pt/CoB/Ir multilayers by means of static domain imaging. First, the temperature dependences of saturation magnetisation (Ms ), exchange stiffness (A) and intrinsic perpendicular anisotropy (Ku) are determined independently, and scaling laws for Ku and D with the magnetisation are established. We then image the demagnetised domain pattern in each multilayer by wide -field Kerr microscopy in the temperature range 9-290 K. We calculate the DMI constant D from an analytical expression for the domain wall energy density that treats the multilayer as a uniform medium. Also, we measure the temperature dependence of the DMI and observe the domain pattern in Pt/CoFeB/Ir and Pt/CoB/Ir multilayers deposited on barium titanate, BaTiO3, (BTO). At room temperature, stripe domains in the Pt/CoFeB/Ir film are tilted along the length of the BTO a-domains, perpendicular to the in-plane tensile strain. The BTO undergoes structural phase transitions at ~180 K and ~ 270 K and these introduce further in-plane strain which we deduce to be responsible for increasing the domain width in the Pt/CoFeB/Ir, as the temperature is increased over the range 13-320 K. The magnetic anisotropy field (μ0Hk) of Pt/CoFeB/Ir and Pt/CoB/Ir multilayers is measured under application of strain. The samples are grown on glass substrates and glued to biaxial piezoelectric transducers. A method based on the extraordinary Hall effect (EHE) is used to measure the magnetic anisotropy field. The strain effects on the anisotropy field, through coupling the films to the piezoelectric transducers, is described and the magnetostriction constant subsequently is measured.