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

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 degrees off the easy-axis position, a property referred to as hard-axis collapse. In such systems a striking phenomenon, recoil-curve overshoot (RCO), recoil mag-netization 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 Ne+ bombardment in vacuum at different ion fluences in the presence of magnetic field Hib applied along different in-plane directions. Ion irradiation at a certain fluence range results in films with easy-magnetization directions parallel to that of Hib. 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.

Automated summary

Distinct sharp peaks in the angular variations of in-plane major-loop remanent magnetization and coercivity, known as hard-axis collapse, were observed in several polycrystalline films. Recent research also discovered recoil-curve overshoot (RCO), where recoil magnetization branches lie outside the major loop, resulting in a significantly larger loop area. In this study, polycrystalline magnetron-sputtered Co films were subjected to Ne+ bombardment at different ion fluences in the presence of a magnetic field, leading to hard-axis collapse and RCO phenomena. Data analysis suggests that these phenomena are primarily caused by domain splitting when the measurement magnetic field is nearly perpendicular to the grain's easy axis.