Composition-tuned magneto-optical Kerr effect in L 1 0 -Mn x Ga films with giant perpendicular anisotropy

We report the large polar magnetooptical Kerr effect in L 1 0 -Mn x Ga (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°, 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 L 1 0 -Mn x Ga films promising for scientific and technological applications in spintronics and terahertz-frequency magnetooptical modulators.