Abstract
As the rapid growth of the internet and multimedia, the demand for high density and small dimension recording increases dramatically. It is inevitable for magnetic recording media to develop more sensitive magnetoresistance devices and high magnetic anisotropy materials in the pursuit of higher recording density. Magnetic nanostructures, such as multilayers and granular solids, have been extensively studied, because of the observation of giant magnetoresistance (GMR). Also, the high magnetic anisotropy materials play a crucial role as the arrival of new recording generation.However, the traditional process will confront the insufficient dilemma as the spin devices forge ahead to the slim and small scale. It is important, therefore, to develop new magnetic recording process. In recent year, ion irradiation has drawn much attention as a potential tool to modify the magnetic properties and magnetic structure. In order to investigate the ion-irradiation effect on the magnetic multilayers, two irradiation topics will be studied: (1) GMR sensor (2) FePt film.This work has focused on the investigation and application in magnetic multilayers. We first used an ion beam or a magnetron sputtering system to deposit F/AF bilayers, PtMn-based spin valves and FePt films. A variety of incident ion dose and energy as well as different magnitude of external magnetic fields and temperatures during ion irradiation was utilized to investigate the correlation between the ion irradiation effect and magnetic behavior.The first topic is the GMR sensors irradiated by carbon ion irradiation. The enhancement of exchange field was observed after irradiation due to the formation of new phase PtMn(C) or NiMn(C). With further increasing ion dose, however, carbon ions residue and intermixing at interface lead to the reduction of exchange field and GMR ratio. By appropriate annealing prior to irradiation, we can obtain an enhanced exchange field and an almost unchanged GMR to solve the problem of interface intermixing. In addition, the exchange field of CoFe/PtMn and CoFe/IrMn can be reversed by C-ion irradiation with external magnetic field antiparallel to the direction of initialized exchange field during irradiation because of the spin direction affected by energy transfer.The second topic is the He-ion irradiation with beam heating in FePt films. The highly ordered FePt L10 phase can be obtained a by using irradiation-induced heating process. Combining the following effects (1) microscopic energy transfer between incident ions and FePt atoms, (2) excess point defects in FePt films and (3) direct beam heating, the ordering of FePt can be achieved at the nominal surface temperature as low as 230℃.Finally, we propose the idea of patterning magnetic multilayers by ion irradiation.