multilayer magnetic structures control the switching field and tighten the switching field distribution in bit patterned media . a strain - inducing layer is excited , e . g ., by a localized magnetic field or a localized thermal heating or a voltage , and induces a strain on the magnetic layer of the patterned bit to initiate switching of the bit magnetization . the strain induced on the magnetic layer forces a rotation or an amplitude variation of the magnetic layer anisotropy . a localized magnetic field is simultaneously or subsequently applied to complete the switching of the bit magnetization . the invention provides control of switching field and switching field distribution for bit - patterned media devices .