A method of magnetising or demagnetising an annular component 200 for a rotary machine is disclosed, the annular component comprising an alternating arrangement of radial elements and angular elements for forming a Halbach array. A magnetizer 310 is caused to induce magnetic flux in a primary set of elements of the annular component comprising a primary radial element 232 and an adjacent primary angular element 222. A shield element 400 shields a secondary angular element 226 of the annular component from magnetic flux from the magnetizer. A flux arrangement for performing a magnetising or demagnetising method is also disclosed, and a flux assembly for such a flux arrangement.