Second Harmonic Light Scattering by Magnetic Dots

Abstract

Subject classification: 75.75.+a; 78.20.LsThe second harmonic light scattering by uniformly and non-uniformly magnetized magnetic dots is theoretically investigated for both s-and p-polarized incident light. It is shown that the contribution of "in plane" and "out of plane" magnetization components of dots can be separated by a polarization analysis of the scattered light at the second harmonic frequency.During the last few years artificial magnetic superstructures of sub-micron sizes were produced using X-ray and electron lithography (see, for example, the review paper [1]). The physical properties of such systems of magnetic particles, or magnetic dots, are intensively investigated because patterned structures are promising for applications as information storage devices [2]. In soft magnetic materials like permalloy (Ni-Fe) there are different possibilities for in-dot magnetization distributions, for example single-domain state or curling state [3]. Usually the isolated cylindrical dots are in a single-domain state ("flower" or nearly uniform state) when the dot radius R < R c (L), where R c (L) is the critical radius and L is the dot thickness [4]. As was shown in Ref.[3], for R > R c (L) a magnetic vortex is formed inside a dot. The vortex states in cylindrical dots were observed in supermalloy (Ni-Fe-Mo) via measurements of hysteresis loops [5] and also for polycrystalline Co [6] as well as in Ni-Fe [7] via magnetic force microscopy. In the case of a two-dimensional ordered dot array, for example, a square magnetic lattice, for typical inter-dot distances the magnetic interaction between the vortex dots is negligibly small and it is possible to consider a magnetic dot in a lattice as an independent particle [8].An effective physical tool for the investigation of regular magnetic dots is magnetooptics [9-13]. Nonlinear optical methods are even more effective than their linear counterparts to investigate magnetic materials, because the nonlinear magneto-optical response is more sensitive for magnetic inhomogeneities, interfaces and superstructures [14]. Magnetization-induced optical second harmonic generation (MSHG) is a very powerful method for the investigation of uniform [14] and non-uniform magnetic structures like magnetic domains and magnetic domain walls [15,16] as well as ordered magnetic structures [17,18]. A polarization analysis of the MSHG signal allows to determine the different components of the magnetization in a magnetic dot. Recent publications devoted to measurements of MSHG in Ni 81 Fe 19 films showed a sufficient nonlinear optical response for excitation with a Ti:sapphire laser with a fundamental wavelength l 0 = 809 nm [19,20].