Estimating Exchange Stiffness of Thin Films With Perpendicular Anisotropy Using Magnetic Domain Images

The exchange stiffness and domain wall width of magnetic thin films with perpendicular magnetic anisotropy are obtained using Kerr microscopy in conjunction with vibrating sample magnetometer measurements. This approach requires only knowledge of saturation magnetization, the effective out-of-plane anisotropy energy, and an image of the demagnetized domain pattern, from which the demagnetization energy and domain wall length are determined. The demagnetization energy is calculated from the image using a Rhodes-Rowlands based approach, while domain wall length is estimated using an image processing algorithm. By relating the effect of domain periodicity on both the demagnetization energy and the domain wall length, an expression for the domain wall energy, and thus exchange stiffness, is constructed. This provides a room-temperature measurement of exchange stiffness in demagnetized unpatterned films. Results are compared with analytical solutions for idealized domain patterns, and a CoFeB/MgO stack is measured as a test case.