Direct laser interference patterning of nonvolatile magnetic nanostructures in Fe60Al40 alloy via disorder-induced ferromagnetism

Abstract

Current magnetic memories are based on writing and reading out the domains with opposite orientation of the magnetization vector. Alternatively, information can be encoded in regions with a different value of the saturation magnetization. The latter approach can be realized in principle with chemical order-disorder transitions in intermetallic alloys. Here, we study such transformations in a thin-film (35 nm) Fe 60 Al 40 alloy and demonstrate the formation of periodic magnetic nanostructures (PMNS) on its surface by direct laser interference patterning (DLIP). These PMNS are nonvolatile and detectable by magnetic force microscopy (MFM) at room temperature after DLIP with a single nanosecond pulse. We provide different arguments that the PMNS we observe originate from increasing magnetization in maxima of the interference pattern because of chemical disordering in the atomic lattice of the alloy at temperatures T higher than the critical temperature T c for the order (B2)disorder (A2) transition. Theoretically, our simulations of the temporal evolution of a partially ordered state at T>T c reveal that the disordering rate is significant even below the melting threshold. Experimentally, we find that the PMNS are erasable with standard thermal annealing at T<T c .

Simulation of Chemical Order–Disorder Transitions Induced Thermally at the Nanoscale for Magnetic Recording and Data Storage

“…We assume that a thin (h ≈ 10 nm) Fe x Al 1−x film can be prepared by sputtering of a target of an alloy with the same composition in a vacuum chamber onto various kinds of substrates, for example, SiO 2 , 28,77 MgO, 27 or Si with a native SiO 2 layer on its surface. 30 The as-prepared CODT alloy is chemically disordered and thus ferromagnetic. 77 The properties of the chosen CODT system, Fe-rich Fe x Al 1−x , needed for our a, lattice constant at room temperature; T sl , average temperature between the solidus and liquidus; T c , critical temperature for the A2−B2 phase transition; E m(v) , activation energy for vacancy migration (formation); D 0 , pre-exponential factor in the Arrhenius law for atomic diffusion; c eq , thermal vacancy concentration at T sl ; μ Fe : B2 (A2), magnetic moment per Fe atom in the B2 (A2) state.…”

“…The validity of this approach is corroborated by the experimental data obtained on formation of magnetic nanostructures in Fe x Al 1−x (x = 0.6) alloys irradiated by interfering laser beams. 30 Microscopically, the CODTs result from atomic diffusion through vacancies in the atomic lattice of a substitutional alloy like Fe x Al t) for the occupation of the site r by an atom of the specific kind A from the fully disordered state, x = N A /N the total concentration of the component A, N A and N are, respectively, the number of atoms of the component A and total number of atomic sites, c v (t) is the vacancy concentration, and Γ(r − r′)xc v is the probability for a jump of an atom A from a site r′ to a site r per a unit of time.…”

“…The amorphous–crystalline phase transitions are accompanied by changes in electrical, ,, optical, − and magnetic , properties of the materials. As a particular kind of PCMs, one can consider intermetallic solid alloys that demonstrate changes in their physical properties due to reversible chemical order–disorder transformations (CODTs), − as illustrated in Figure a (bottom panel). An initially disordered alloy tends to be ordered under thermal treatment below the critical temperature T c .…”

“…The system tends to structural (chemical) ordering at T < T sl ( T < T c ), while it tends to structural (chemical) disordering at T > T sl ( T > T c ). (b) Magnetization magnitude as a function of time under A2–B2 transformations in CODT alloys, for example, Fe x Al 1– x . − (c, d) Conceptual differences between the proposed approach and current magnetic memories. In tops of the panels, bits of binary information in (c) currently existing magnetic recording media and (d) proposed CODT alloys are shown.…”

Coupled Electromagnetic and Reaction Kinetics Simulation of Super-Resolution Interference Lithography

“…Two-color photoresists with inhibition intensity thresholds that are several orders of magnitude lower , can be used in interference lithography configurations that involve the exposure of a photosensitive medium to two or more coherent beams of light. Interference lithography is inherently configured to support large-area coverage, albeit at the cost of being restricted to periodic patterns. − Feature sizes on the order of tens of nanometers have been demonstrated in thin films and monolayers while using visible light in super-resolution inspired interference lithography configurations. − …”