Printing Nearly-Discrete Magnetic Patterns Using Chemical Disorder Induced Ferromagnetism

Abstract

Ferromagnetism in certain alloys consisting of magnetic and nonmagnetic species can be activated by the presence of chemical disorder. This phenomenon is linked to an increase in the number of nearest-neighbor magnetic atoms and local variations in the electronic band structure due to the existence of disorder sites. An approach to induce disorder is through exposure of the chemically ordered alloy to energetic ions; collision cascades formed by the ions knock atoms from their ordered sites and the concomitant vacancies are filled randomly via thermal diffusion of atoms at room temperature. The ordered structure thereby undergoes a transition into a metastable solid solution. Here we demonstrate the patterning of highly resolved magnetic structures by taking advantage of the large increase in the saturation magnetization of Fe60Al40 alloy triggered by subtle atomic displacements. The sigmoidal characteristic and sensitive dependence of the induced magnetization on the atomic displacements manifests a sub-50 nm patterning resolution. Patterning of magnetic regions in the form of stripes separated by ∼ 40 nm wide spacers was performed, wherein the magnet/spacer/magnet structure exhibits reprogrammable parallel (↑/spacer/↑) and antiparallel (↑/spacer/↓) magnetization configurations in zero field. Materials in which the magnetic behavior can be tuned via ion-induced phase transitions may allow the fabrication of novel spin-transport and memory devices using existing lateral patterning tools.

Realization of a spin-wave multiplexer

“…Furthermore, the same approach can be adapted to ferromagnetic insulators, such as yttrium iron garnets, where the damping of the magnetization dynamics is greatly reduced and therefore the spin-wave propagation distance is significantly increased. Another approach to reduce the currents required to magnetize the spin-wave waveguide perpendicular to the transport direction is to use ion implantation to imprint waveguides into paramagnetic or ferromagnetic films 24,25 . In such waveguides the shape anisotropy is strongly reduced due to the surrounding ferro-or paramagnetic environment.…”

Tuning the antiferromagnetic to ferromagnetic phase transition in FeRh thin films by means of low-energy/low fluence ion irradiation

“…In such alloys, varying the degree of chemical order can be a lever to modify the magnetic behaviour [1][2][3][4]. In particular, the chemically disordered state, where the atomic site occupancies have been randomized, is metastable.…”

“…Moreover, ion-irradiation is suited for magnetic film patterning on micro-and nanoscale, i.e. using shadow masks or focused ion beam techniques [1,3,5]. A model system to study disorder induced magnetic phenomena is Fe 1Àx Al x with composition around x = 0.4 [1].…”

“…For such a composition, FeAl thin films are paramagnetic in the chemically ordered and ferromagnetic in the disordered state. Ion beam patterning by means of Ne + ion irradiation revealed highly resolved para-and ferromagnetic areas [1,3]. By adjusting the dimensions of the ferromagnetic regions, reprogrammable parallel and antiparallel magnetisation configurations in zero field have been achieved [3].…”

Magnetization Reversal of Disorder-Induced Ferromagnetic Regions in Fe₆₀Al₄₀ Thin Films

“…Recently, magnetic patterning of stripe structures with sub-50 nm resolution has been demonstrated on Fe 60 Al 40 wires [12]. In this paper, we have studied the dynamics of the magnetization reversal based on domain imaging in a similar system of Ne + irradiated ferromagnetic Fe 0.6 Al 0.40 40 nm thick films: 1) uniformly irradiated continuous film, irradiated with 22.5 keV Ne + ions and a fluence of 6 14 ions/cm −2 ; 2) uniformly irradiated wire 10 μm wide, irradiated with 20 keV Ne + ions at the same fluence; and 3) 10 μm wide wire patterned by stripes with alternating 2 and 0.5 μm widths, respectively, separated by~40 nm wide weakly magnetic spacers.…”