Large Nonlinear Kerr Angle in non-Centrosymmetric Fe/AlGaAs (001) Heterostructure
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0941-Q02-07
Large Nonlinear Kerr Angle in non-Centrosymmetric Fe/AlGaAs (001) Heterostructure Haibin Zhao1, Diyar Talbayev1, Gunter Luepke1, Aubrey Hanbicki2, Connie Li2, and Berend Jonker2 1 The College of William and Mary, Williamsburg, VA, 23187 2 Naval Research Laboratory, Washington, DC, 20375
Abstract A large nonlinear magneto-optical effect is observed in a non-centrosymmetric Fe/AlGaAs (001) heterostructure. This effect is a direct consequence of interference between second-harmonic optical waves of magnetic and crystallographic origin, generated at ferromagnetic Fe interface and bulk AlGaAs, respectively. The longitudinal nonlinear Kerr rotation is measured to be 1.6o along the [1-10] hard axis, about two orders of magnitude stronger than the linear equivalent. The rotational second-harmonic signal shows large magnetic contrast along all the in-plane directions, demonstrating a high sensitivity to the magnetization of an anisotropic interface in the longitudinal geometry.
Introduction The nonlinear magneto-optical Kerr effect is sensitive to surface and interface magnetization in centrosymmetric thin films [1,2] and multilayers [3] due to the fact that the crystallographic bulk contribution to second harmonic generation (SHG) is forbidden in centrosymmetric materials in electric dipole approximation. Moreover, the magnetization does not break the inversion symmetry in the bulk but can lower the surface and interface symmetry, leading to magnetization-induced SHG (MSHG) only from the latter [4]. In this case, magnetization-induced components in MSHG are comparable in magnitude with components of non-magnetic origin, which leads to high magnetic asymmetry and large nonlinear magnetooptical Kerr angle [5]. This intrinsic sensitivity, however, has so far only been shown for centrosymmetric structures. In this paper, we will demonstrate a large nonlinear magneto-optical effect from buried Fe interface in a noncentrosymmetric Fe/AlGaAs hybrid structure. The nonlinear magneto-optical Kerr angle is measured to be 1.6o, which is about two orders of magnitude stronger than the linear equivalent.
Theory For a particular magneto-optical configuration, the optical second-harmonic polarization P (2ω) of the magnetic medium can be described by one third-rank nonlinear susceptibility tensor with different components [4], which are either even or odd in magnetization M, describing the crystallographic or the magnetization-induced contribution, respectively: Pi (2ω ,± M ) = ( χ ijk+ (± M ) ± χ ijk− (± M )) E j (ω ) E k (ω ) .
(1)
The odd components χ ijk− change sign upon magnetization reversal and therefore give rise to the magnetic asymmetry in the MSHG response. The measured intensity in a fixed experimental geometry with opposite magnetization direction can be written as a sum of effective tensor components: I ± (2ω ) ∝ χ eff+ (2ω ) ± χ eff− (2ω )
2
(2)
where χ eff+ and χ eff− are linear combinations of the even and odd tensor elements and Fresnel factors α ijk :
χ eff =
∑α
ijk
χ ijk
(3)
i, j ,k
The magn
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