Ultrasensitive transverse magneto-optical Kerr effect measurements using an effective ellipsometric detection scheme

Abstract

We present a new methodology that enables a significant sensitivity improvement for transverse magneto-optical Kerr effect (T-MOKE) detection. For this purpose, we developed a novel measurement scheme, in which the polarization detection conditions are changed during the measurement sequence in a pre-defined way. An analytical expression of the associated T-MOKE signal pattern was derived, which allowed us to analyze and classify our experimental data in a straightforward way. Furthermore, this new measurement approach enables the identification of noise and false background signals that might be generated by the sample under investigation, the environment or the detection system itself and it provides a pathway to unambiguously separate all these effects from true T-MOKE signals. These capabilities significantly increase the sensitivity and robustness of T-MOKE detection. The method enabled us to measure magneto-optical signals for samples that are paramagnetic at room temperature or exhibit really small magneto-optical responses, even in the presence of false signals that were far larger in size. Our new methodology was integrated into a scanning wafer tool, which allows for nondestructive, laterally resolved surface characterization measurements and even has the capability of measuring optical and magneto-optical properties simultaneously.

Sensitivity and reproducibility of transverse magneto-optical Kerr effect (T-MOKE) ellipsometry

“…of T-MOKE experiments is the experimental geometry of the set-up, because it allows for a more flexible design due to the spatial separation of the optical elements from the magnetic field generating components, which are arranged in perpendicular planes [37]. In the pure intensity measurement mode, T-MOKE usually produces weaker signal amplitudes than L-and P-MOKE [38,39], but previous works have demonstrated that with the effective polarization detection measurement scheme [37,40], the sensitivity of T-MOKE measurements can be improved significantly and made comparable to L-MOKE measurements [37,40].…”

“…Therefore, T-MOKE measurements can be performed as polarization measurements. An additional improvement of the sensitivity has been achieved via an ellipsometric approach [37]. Hereby, the ellipse that represents the polarization state of the reflected light is determined, so that the relative change in polarization can be measured with very high accuracy.…”

“…Hereby, the ellipse that represents the polarization state of the reflected light is determined, so that the relative change in polarization can be measured with very high accuracy. Moreover, the magneto-optical polarization modification is superimposed onto purely optical polarization modifications, so that both optical and magneto-optical effects can be accurately measured [37]. For T-MOKE ellipsometry measurements, the effective polarization detection conditions are changed during the measurement sequence, and in conjunction with the corresponding data analysis, this method was demonstrated to be able to obtain full magneto-optical and optical sample information, as well as isolate noise and false background signals.…”

“…For T-MOKE ellipsometry measurements, the effective polarization detection conditions are changed during the measurement sequence, and in conjunction with the corresponding data analysis, this method was demonstrated to be able to obtain full magneto-optical and optical sample information, as well as isolate noise and false background signals. Key experimental aspects of this T-MOKE ellipsometry method were already discussed in [37].…”

Improving the sensitivity of DC magneto-optical Kerr effect measurement to 10−7rad/Hz

“…By inserting reflection optics to fold the obliquely-incident beam path backward, the modified Sagnac interferometer can be applied to measure the in-plane magnetization with a sensitivity of 10 −6 rad= Hz p [19,20] . Another widely used approach is based on high-frequency modulation of the sample magnetization, which may reach the lowest noise floor of several 10 −9 rad with sensitivity of ∼10 −7 rad= Hz p [7,21,22] . Unfortunately, to date, the detection limit of DC MOKE is limited to ∼2 × 10 −7 rad 10 −5 deg [15] , which hinders the study of the static in-plane and out-of-plane magnetic properties, such as TRSB states in Sr 2 RuO 4 [17] and PrOs 4 Sb 12 [23] .…”