RU2560148C1 - METHOD OF MEASURING MAGNETOOPTICAL EFFECTS in situ - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: analysed sample is illuminated with a linearly polarised light beam and change in polarisation upon reflection is measured using separation of the reflected beam into p- and s-components with amplitude and phase decomposition to obtain four light beams at the output. An alternating magnetic field is applied to the analysed sample during measurement. The polariser is fixed at position P=0 when measuring the longitudinal Kerr effect and analysers in amplitude and phase channels A_1,2=45°. Remagnetisation of the sample is carried out using a rotating permanent magnet and the polarisation rotation value α, which is proportional to the projection of magnetisation intensity on the plane of incidence of light, is determined using a formula.

EFFECT: high measurement accuracy and information value.

3 dwg

Description

The invention relates to the field of magnetic and magneto-optical measurements and can be used to quickly characterize magnetic materials, obtain spectral dependences of magneto-optical effects, as well as the dependences of the magneto-optical signal on the applied magnetic field. The method allows the use of standard instruments that measure the state of polarization, commercially available ellipsometers for measuring not only classical ellipsometric angles, but also magneto-optical parameters, which can extract information about the magnetic state of the sample, in particular, obtain hysteresis loops by registering a magneto-optical response proportional to the magnetization in the sample under study.

A known method of measuring the state of polarization with an ellipsometer [pm RF №16314, IPC С01N 21/21, publ. 20.12.2000], constructed according to the photometric scheme, which consists in splitting the light beam reflected from the surface of the test sample into two components, which measure the amplitude and phase changes in light during reflection, respectively, for p and s polarizations.

The disadvantages of this method are the low accuracy of the measurements and the narrow spectral range of the measurements, as well as in the case of a ferromagnetic sample of the impossibility of recording a magneto-optical response when a magnetic field affects the system under study.

The closest technical solution to the claimed is a method of measuring the state of polarization with an ellipsometer [RF patent No. 2302623, IPC: 6 СN 21/21, publ. 07/10/2007 (prototype)], which consists in the fact that the design also uses a photometric scheme, which allows minimizing the time of a single measurement in such a way that this configuration can be adapted to measure magneto-optical effects.

The technical result consists in increasing the accuracy of measurement and information content in order to measure magneto-optical effects in situ.

The technical result is achieved by the fact that in the method of measuring magneto-optical effects in situ, namely, that the test sample is illuminated with a linearly polarized light beam and the change in polarization upon reflection is measured using separation of the reflected beam into p- and s-components with expansion in amplitude and phase to yield four light beams with intensities I _1, I _2, I _3, I _4, new is the fact that to the sample during the measurement alternating magnetic field is applied, when measuring meridion Kerr effect polarizer ceiling elements fixed in position P = 0, and analyzers in the amplitude and phase channels A _1,2 = 45 ° and the sample magnetization reversal is performed by a rotating permanent magnet, in which case the value of polarization plane rotation α, proportional to the projection of the magnetization in the plane of incidence light is determined by the formula:

,

,

where α is the angle of rotation of the plane of polarization, I ₁ I ₂ are the intensities of the p and s components in the amplitude measuring channel of the analyzer arm, and when measuring the equatorial Kerr effect, the sample is magnetized by means of an electromagnet, the polarizer is fixed in position P = ± 45 °, and analyzers in the amplitude and phase channels A _1.2 = 45 °, while the magneto-optical response proportional to the intensity of the p-component is determined by the formula:

,

,

where β is the signal of the equatorial Kerr effect, I ₁ is the intensity in the amplitude channel, k is the proportionality coefficient, which depends on the parameters of the studied sample.

The differences of the proposed method from the closest analogue are that an alternating magnetic field is applied to the test sample during measurements, as well as in the used mathematical apparatus when calculating the values of the magneto-optical signal. These differences allow us to conclude that the proposed technical solution meets the criterion of "novelty." Signs that distinguish the claimed technical solution from the prototype are not identified in other technical solutions when studying this and related areas of technology and, therefore, provide the claimed solution with the criterion of "inventive step".

In FIG. 1 shows a schematic of a magneto-ellipsometric complex in situ.

A device for measuring magneto-optical effects in situ (FIG. 1) consists of a light source 1 (HeNe laser), a polarizer 2, comprising the polarizer arm, high-vacuum windows 4 and 10 for input and output of an optical beam, respectively, of a high-vacuum chamber 5, of the sample 6 . To create an alternating magnetic field in the plane of the sample, a manipulator 8 with a constant NdFeB magnet 7 (for measuring the meridional Kerr effect (IEC) or an electromagnet 9 (for measuring Equatorial Kerr effect (EEC)) .In addition, the technical design is made in such a way that only the p-component of the beam is used in the MEK measurement. Also, during measurements, the accuracy is improved by averaging the data arrays obtained over several revolutions of the manipulator 8 in the case of MEK measurement , and in the case of measuring the EEC, the data are accumulated over several periods of magnetization reversal.The arm of the analyzer of the magneto-ellipsometric complex consists of a beam splitting element 11, a phase-shifting element 13, etc. Wollaston gp 12, 14, dvuhploschadnyh photodetectors 15. Also shown in FIG. 1 shows the integral components of a growth vacuum chamber for applying thin layers and coatings: molecular sources (evaporators) 16 and their shutters 17.

Measurements of the magneto-optical Kerr effect are as follows.

The light flux 3 emitted by the illuminator 1 is linearly polarized by the polarizer 2, and passing through the ultra-high vacuum window 4, it enters the ultra-high vacuum chamber 5, and then falls onto the surface of the test sample 6. During measurements, a magnetic field is applied to the sample or using a permanent magnet 7 driven by a manipulator 8, or by an electromagnet 9. An incident, linearly polarized light beam is reflected from the surface of the sample under the influence of a magnetic field, with a change m of the polarization state due to the Kerr effect in the magnetic sample, and becomes, in the general case, elliptically polarized and, in this state, leaving the high-vacuum chamber through the high-vacuum window 10, enters the analyzer arm, namely, the composite light beam splitter 11, splitting the light beam reflected by the studied sample into two light components, one of which falls into the amplitude measuring channel ψ, where the Wollaston prism 12 divides the input light beam into p and s components, the characteristics of which are then recorded by a two-area photodetector 15. Another part of the light beam enters the phase measuring channel Δ, where, passing through the phase-shifting element 13 and the Wollaston prism 14, they are also recorded by photodetectors 15.

As a result, we have four intensity values I ₁ , I ₂ , I ₃ and I ₄ , from which the values of the classical ellipsometric angles ψ and Δ are calculated. During such measurements, the optical polarizing elements can take the following fixed positions:

- polarizer: P = 0 or ± 45 °;

- the analyzer in the channel ψ: A ₁ = 0 or 45 °;

- compensator - C = 0 °;

- the analyzer in the channel Δ: A ₂ = 0 or 45 °.

Of the available configurations of optical elements [Shvets et al. Optics and Spectroscopy, 2004, vol. 97, No. 3, pp. 514-525], the most practical is the configuration in which the optical elements are in the positions: A ₁ = 0, C = 0, A ₂ = 45 (configuration I) and A ₁ = 45, C = 0, A ₂ = 45 (configuration II). For the marked configurations, the following relations between the ellipsometric parameters and the measured signals are fulfilled:

Configuration I:

F _ψ = -cos2ψ

F _Δ = ± sin2ψcos (Δ + δ _s )

Configuration II:

F _ψ = ± sin2ψcosΔ

F _Δ = ± sin2ψcos (Δ + δ _s )

,

, δ_с - фазовый сдвиг компенсатора, I₁, I₂, I₃, I₄ - сигналы с фотоприемников каналов ψ и Δ. Знак ± в формулах соответствует положениям поляризатора P=45 и -45°.where ψ and Δ are the measured ellipsometric parameters,

,

, δ _с - phase shift of the compensator, I ₁ , I ₂ , I ₃ , I ₄ - signals from the photodetectors of the channels ψ and Δ. The sign ± in the formulas corresponds to the positions of the polarizer P = 45 and -45 °.

Ellipsometric parameters are calculated as follows:

Configuration I:

$$\psi =\frac{\mathrm{one}}{2}\arccos (-F_{\psi })$$

Δ = p arccos (± F _Δ / sin2ψ) -δ _c

where the value p = 1 or -1, defining the range Δ, remains undefined within this configuration and is set by the operator by selecting the range Δ.

Configuration II:

или

or

.

.

The meridional Kerr effect consists in the appearance of the s-component upon reflection of a wave linearly polarized in the plane of incidence. In this case, the polarization vector is rotated by a small angle α, which is to be determined when measuring with an ellipsometer-magnetometer. During MEK measurements, the polarizer is fixed in position P = 0, and the analyzers in channels A _1.2 = 45 °.

A rotation of the plane of polarization as a result of the Kerr effect leads to a redistribution of the intensities of the light flux incident on the photodetectors 15 (depending on the sign of the effect, the intensity on one photodetector will increase in proportion to sin2α, and on the other it will decrease by the same amount).

The rotation of the plane of polarization during magnetization reversal of the sample by a rotating magnetic field for IEC is calculated by the formula:

,

,

where α is the angle of rotation of the plane of polarization, I ₁ I ₂ are the intensities of the p- and s-components in the amplitude measuring channel ψ of the analyzer arm.

In FIG. Figure 2 shows the results of MEK measurements in a 5-nm-thick DyNi layer of the Ni [8nm] / DyNi [5nm] two-layer structure. The experimental data are presented as a rotation of the plane of polarization as a function of the angular coordinate of the direction of the magnetic field with respect to an arbitrary direction in the plane of the sample. When measuring the equatorial Kerr effect, the sample is magnetized by means of an electromagnet 9, the polarizer is fixed in position P = ± 45 °, and the analyzers in channels A are _1.2 = 45 °, while the magneto-optical response is proportional to the intensity of the p-component:

β = kI ₁ ,

where β is the signal of the equatorial Kerr effect, I ₁ is the intensity in the amplitude channel, k is the proportionality coefficient, which depends on the parameters of the studied sample.

In FIG. Figure 3 shows the results of EEC measurements in an iron film 10 nm thick on a single-crystal silicon substrate. The experimental data are presented as the dependence of the EEC signal on the magnitude of the applied magnetic field.

The advantages of the proposed method for measuring magneto-optical effects in situ are:

- in expanding the capabilities of a standard ellipsometer;

- the possibility of measuring with fast magnetization reversal;

- the possibility of spectral measurements of magneto-optical effects.

Claims (1)

A method for measuring magneto-optical effects in situ, namely, that the test sample is illuminated with a linearly polarized light beam and the change in polarization upon reflection is measured using separation of the reflected beam into p- and s-components with expansion in amplitude and phase, obtaining four light beams at the output with intensities I _1, I _2, I _3, I _4, characterized in that to the sample during the measurement alternating magnetic field is applied, when measuring the longitudinal Kerr effect polarizer fixed in Assumption P = 0, and analyzers in the amplitude and phase channels A _1,2 = 45 ° and the sample magnetization reversal is performed by a rotating permanent magnet, in which case the value of polarization plane rotation α, proportional to the projection of the magnetization at the light incidence plane is given by:

,
where α is the angle of rotation of the plane of polarization, I ₁ , I ₂ are the intensities of the p and s components in the amplitude measuring channel of the analyzer arm, and when measuring the equatorial Kerr effect, the sample is magnetized by means of an electromagnet, the polarizer is fixed in position P = ± 45 °, and analyzers in the amplitude and phase channels A _1.2 = 45 °, while the magneto-optical response proportional to the intensity of the p-component is determined by the formula:

where β is the signal of the equatorial Kerr effect, I ₁ is the intensity in the amplitude channel, k is the proportionality coefficient, which depends on the parameters of the studied sample.

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