Abstract: Methods and apparatus for reversibly altering magnetic characteristics or domains of ferrimagnetic material by photomagnetic means, particularly by electron spin reversal (spin-flip). Photomagnetic electron spin reversal and inversion creating cylinder domains and their surrounding toroid domains of oppositely directed intrinsic magnetization in ferrimagnetic thin film material are achieved by means of signal modulated circularly polarized laser radiation. Three different stable conditions are detectable. The invention has particular application as a fundamentally new aproach to erasable digital data storage, providing means and methods for photomagnetically alterable and erasable data storage which can be detected by observing polarization of optical radiation directed through the ferrimagnetic material.