Method and apparatus for controlling topographical variation on a milled cross-section of a structure

A method of exposing a non-planar cross-section of a write-head pole structure composed of a first material, the method comprising:

• depositing a protective overcoat layer of a second material on said write-head pole structure, said protective overcoat layer coating the exterior of the write-head pole structure, said second material having ion beam mill rates at higher incidence angles that do not closely approximate the ion beam mill rates of the first material at the same incidence angles, the difference in the ion beam mill rates of the first material and the second material being due to different material properties of the first material and second material;
• directing an ion beam at the write-head pole structure;
• exposing, by means of milling the write-head pole structure using the ion beam, a cross-section of the write-head pole structure;
• and
• producing, by means of milling the write-head pole structure using the ion beam, a non-planar face on said exposed cross-section;
• in which the second material is elemental tungsten.