The subwavelength tuned magneto-optical Kerr effect in L1 ₀ -FePt films with perpendicular magnetic anisotropy

Abstract

We report the large polar magnetooptical Kerr effect in L10-MnxGa (0.76 ≤ x ≤ 1.29) epitaxial films with giant perpendicular magnetic anisotropy. The Kerr rotation is enhanced by a factor of up to 2.5 by decreasing Mn atomic concentration, which most likely arises from the variation of the effective spin-orbit coupling strength, compensation effect of magnetic moments at different Mn atom sites, and overall strain. A significant tuning effect of composition is also observed on Kerr ellipticity and complex Kerr angle (including the magnitude and phase angle). The good epitaxial compatibility with semiconductors, moderate coercivity of 4.6-9.7 kOe, large Kerr rotation of up to 0.10 o , high reflectivity of 35%-55% in a wide wavelength range of 400~850 nm, and giant magnetic anisotropic field of up to 140 kOe together make these L10-MnxGa films promising for scientific and technological applications in spintronics and terahertz-frequency magnetooptical modulators. 1. Introduction The polar magneto-optical (MO) Kerr effect is a powerful tool that can locally probe the magnetic properties and electronic structures of materials [1] and modulate the optical polarization at the spin precession frequency [2]. Most recently, a variety of new exciting spintronic phenomena have been observed taking advantage of the polar MO Kerr effect, such as voltage-controlled magnetic anisotropy in ferromagnetic thin films [3], broken time-reversal symmetry in the heavy-fermion superconductors and bilayer graphene [4,5], terahertz spin precession in perpendicularly magnetized Mn3Ge films [6], spin Hall effect in semiconductors [7], magnetic skyrmion bubbles [8], magnetic vortex dynamics [9], spin orbit torques [10], and nanosecond current-induced domain wall motion [11] in ferromagnet/heavy metal bilayers and nanowires. From the viewpoint of technological application, high-speed optic communication requires modulators of light magnitude/polarization working at very high frequencies. For MO modulators, the conventional ferromagnetic materials, e.g. Permalloy, usually have very weak magnetic anisotropy which limits the modulation bandwith to a few GHz or less [2]. MO materials with giant magnetic anisotropic field (Hk) of ~100 kOe, e.g. Mn3Ge [6], are good candidates for ultrafast MO modulators due to their terahertz-frequency spin precession, which is at least two orders of magnitude faster than that based on conventional ferromagnetic materials [2]. Furthermore, MO materials epitaxially compatible with semiconductors allow for direct integration of MO functional devices with underlying photonic circuits. Therefore, for both the spintronic and modulator applications [6-11], it is highly desirable to develop new kinds of MO materials which simultaneously have large saturation Kerr rotation (θK), high optical reflectivity (R), giant Hk, and good semiconductor compatibility, and to further tailor their MO properties. In past two decades, the noble-metal-free and rare-earth-free MnxGa alloys with giant uniaxial magnetic

Resonant magneto–optical Kerr effect induced by hybrid plasma modes in ferromagnetic nanovoids

“…With PSS arrayed on the ferromagnetic films, the effective permittivity εxx has been manipulated through introducing surface modes and demonstrating the enhanced MOKE of Fe film. [54][55][56][57] Here, in 2D nanostructured ferromagnetic voids, besides surface lattice resonance modes, the noble metal substrate effects and nanocavity modes have been manipulated by controlling the depth of the voids. From the Lorentz line shape analysis of θ k and ε k according to Eq.…”

“…Besides the basic physical research and MO setups such as modulators and isolators, materials with resonant MOKE are urgent for optical biosensors. [66][67][68][69][70][71] The sensitivity can be extrapolated according to [55] S…”

“…[51] In 2D magnetic nanoparticle arrays, Fano-type profile has been revealed in the MOKE spectrum due to the coupling between surface lattice plasmons that occurred in the orthogonal directions. [52,53] The modulated MOKE signal of ferromagnetic films through PSS array caped have been studied in our former work, [54][55][56][57] where the PSS array, as two-dimensional gratings, plays a key role in surface mode occurrence. Whereas in Co/Pt nanocaps fabricated on the PSS array template, MOKEs are modulated by SPP and Mie scattering optical modes.…”