In-Situ Investigation of Ion Beam-Induced Crossover in Uniaxial Magnetic Anisotropy of Polycrystalline Fe Films

Abstract

A combined role of structure and morphology of polycrystalline Fe thin films in the evolution of uniaxial magnetic anisotropy (UMA) subjected to several cycles of the ion beam erosion (IBE) process is investigated through a set of self-consistent in-situ experiments. In the initial stages of IBE, surface texturing of the Fe film imprints a recognizable magnetocrystalline anisotropy (MCA) with the easy axis of magnetization along the IBE direction. Further erosion results in development of a well-defined correlated morphology that incorporates reinforcement of stray dipolar fields and switches the easy axis of magnetization by 90°. The observed unusual crossover is inferred to be originated from an interplay between the relative weight of MCA and shape anisotropy, which is successfully explained by considering the modified surface structure, morphology, and the relative strength of the dipolar stray fields. The present phenomenological understanding provides a promising option of the fine tailoring of UMA strength by controlling crystallinity of the surface along with anisotropic morphology patterns.

Dependence of magnetic domain patterns on plasma-induced differential oxidation of CoPd thin films

“…As H c decreases with time, one can see that H c inside the squares generally stays lower than that outside, except for the Day-42 case, where H c inside is higher, exhibiting an opposite effect of evolving oxidation on H c , which leads to a reversed outcome of the domain patterns on Day 42. The difference between H c inside the square (exposed to plasma) and that outside (without plasma exposure) is largest on Day 10 with ∆H c = 10 Oe, which has a magnitude comparable with the decrement in H c accomplished by 2-keV ion beam erosion [19]. It is quite intriguing that modification of the surface MAE with the surface plasma treatment can determine the magnetic domains of the whole continuous magnetic film.…”

“…In magnetic engineering, ion irradiation has long been considered a reliable process to create magnetic domain patterns with the penetration of keV to MeV ions into the films of magnetic materials [17,18,19]. Treatments with ions of sufficient energy are believed to be a requirement for successful modification of the magnetic coherence and coupling in a magnetic film in order to generate artificial magnetic microstructures inside the film.…”

Morphology induced large magnetic anisotropy in obliquely grown nanostructured thin film on nanopatterned substrate

“…Interfacial morphology and symmetry breaking effect at the nanoscale strongly influence magnetic response of a material such as magnetic anisotropy [1], coercivity [2], magnetization reversal process [3], hysteresis [4], magneto-resistance [5]. In particular, magnetic anisotropy that relies on the preferred orientation of the spin alignment [6] of a thin film structure have extensively finds its application in the spintronics industry [7], perpendicular spin valves [8], magnetic tunnel junction devices [9] as well as other applications in magnetoelectronics [10], high-density storage media [11], and magnetic sensors [12]. Therefore, tailoring of magnetic anisotropy (MA) by modifying the surface and interface morphology is a fascinating field of research.…”

“…The film deposited on rippled substrates exhibits strong magnetic anisotropy [29,30,31], which is driven by morphological anisotropy. Direct nanoscale ripple patterning can also induce in-plane UMA in epitaxial [32] and polycrystalline [5,6] thin films. For the film deposited over the rippled substrate, the saturation in the strength of UMA with higher film coverage due to the merging of ripples with their nearest neighbours is still an open issue [1,29,33,34].…”

“…As the topographic condition strongly influences thin film's growth, oblique incidence defocused broad ion beam surface patterning potentially offers an easy and inexpensive solution to prepattern the surface, which can be used as a template for the overgrowth structures [35][36][37]. Several discrete studies on morphology and magnetic anisotropy of the two distinguished systems, i.e., obliquely grown film on bare substrate and film deposited on the rippled patterned substrate, have been investigated thoroughly for different systems [2,5,6,24,30,32]. Few works on coupled oblique-ripple systems have been done in the recent past, emphasizing morphology or optical property [35,[38][39][40].…”