High precision magnetic linear dichroism measurements in (Ga,Mn)As

Abstract

Investigation of magnetic materials using the first-order magneto-optical Kerr effects (MOKEs) is well established and is frequently used. On the other hand, the utilization of the second-order (or quadratic) magneto-optical (MO) effects for the material research is rather rare. This is due to the small magnitude of quadratic MO signals and the fact that the signals are even in magnetization (i.e., they do not change a sign when the magnetization orientation is reversed), which makes it difficult to separate second-order MO signals from various experimental artifacts. In 2005 a giant quadratic MO effect-magnetic linear dichroism (MLD)-was observed in the ferromagnetic semiconductor (Ga,Mn)As. This discovery not only provided a new experimental tool for the investigation of in-plane magnetization dynamics in (Ga,Mn)As using light at normal incidence, but it also motivated the development of experimental techniques for the measurement of second-order MO effects in general. In this paper we compare four different experimental techniques that can be used to measure MLD and to separate it from experimental artifacts. We show that the most reliable results are obtained when we monitor the polarization of reflected light while the magnetization of the sample is rotated by applying an external magnetic field. Using this technique we measure the MLD spectra of (Ga,Mn)As in a broad spectral range from 0.1 eV to 2.7 eV and we observe that MLD has a magnitude comparable to the polar MOKE signals in this material.

Systematic study of magnetic linear dichroism and birefringence in (Ga,Mn)As

“…The sample substrates were wedged (1 • ) to avoid spurious signals that might appear due to the multiple reflections from the back side of the substrate. In order to measure the rotation and ellipticity angles θ and ψ in a broad energy range we developed a sensitive experimental technique which is described in detail in [18]. We use a Xe lamp (0.33-2.7 eV) with a double prism CaF 2 monochromator and discrete spectral lines from CO 2 (115-133 meV) and CO (215-232 meV) lasers [33].…”

“…In analogy with the dc anisotropic magnetoresistance, it crucially depends on the spin-orbit interaction in the whole spectral range. Previous experiments have focused on measurements of the even in M magneto-optical effects in selected (Ga,Mn)As samples without studying their spectral dependence [17] or limiting themselves to the visible spectral range [4,18], Here, we report measurements in a spectral range of 0.12-2.7 eV and study systematically the magneto-optical spectra even in M across a series of optimized (Ga,Mn)As materials spanning a broad Mn-doping range summarized in Table I below.…”

Comparison of micromagnetic parameters of the ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As

“…The rotation of the probe polarization plane is caused by two MO effects-the polar Kerr effect and the magnetic linear dichroism, which are sensitive to perpendicular-to-plane and in-plane components of magnetization, respectively [31][32][33]. For all MO experiments, samples were mounted in a cryostat and cooled down to ≈15 K. The cryostat was placed between the poles of an electromagnet, and the external magnetic field H ext ranging from ≈0 to 585 mT was applied in the sample plane, either in the [010] or [110] crystallographic direction of the sample (see inset in Fig.…”

“…(9) are connected with the out-of-plane and in-plane movement of magnetization, and the last term describes a change of the static MO response of the sample due to the laser-induced demagnetization [31]. P PKE and P MLD are MO coefficients that describe the MO response of the sample, which we measured independently in a static MO experiment [32,33], and β is the probe polarization orientation with respect to the crystallographic direction [100] [31]. To further simplify the fitting procedure, we can extract the oscillatory parts from the measured MO data (cf.…”

Collective magnetization dynamics in ferromagnetic (Ga,Mn)As mediated by photoexcited carriers

“…[28][29][30] The experiments were performed in a Janis subcompact cryostat at various temperatures. No external magnetic field was applied in the experiments.…”