Ion irradiation induced direction of collapsed hard-magnetization axis in thin Co films

Abstract

A number of polycrystalline films feature distinct sharp peaks in the angular variations of their in-plane major-loop remanent magnetization and coercivity, centered ${90}^{\ensuremath{\circ}}$ off the easy-axis position, a property referred to as hard-axis collapse. In such systems a striking phenomenon, recoil-curve overshoot (RCO), recoil magnetization branches that lie outside the major loop, was recently reported, resulting in a significantly greater recoil loop area compared with that of the respective major loop. In the present work pieces of polycrystalline magnetron-sputtered Co films were subjected to ${\mathrm{Ne}}^{+}$ bombardment in vacuum at different ion fluences in the presence of magnetic field ${H}_{ib}$ applied along different in-plane directions. Ion irradiation at a certain fluence range results in films with easy-magnetization directions parallel to that of ${\mathbf{H}}_{\mathbf{ib}}$. Moreover, the same holds for posterior sequential irradiations. The films' hard-magnetization axes are always collapsed, accompanied by significant RCO as well. The analysis and interpretation of our data strongly indicate that both hard-axis collapse and RCO result predominantly from a domain splitting when the measurement magnetic field is nearly perpendicular to the grain's easy axis during demagnetization.