CN108680879B - Nano-structure magnetic measurement method - Google Patents
Nano-structure magnetic measurement method Download PDFInfo
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- CN108680879B CN108680879B CN201810429273.6A CN201810429273A CN108680879B CN 108680879 B CN108680879 B CN 108680879B CN 201810429273 A CN201810429273 A CN 201810429273A CN 108680879 B CN108680879 B CN 108680879B
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Abstract
The invention relates to the technical field of physical measurement, in particular to a method for measuring the magnetism of a nanostructure, wherein a measuring device comprises a laser, a beam splitter, a convex lens I, a photoelectric detector, a phase-locked amplifier, a prism polarizer, a convex lens II, a polarization-maintaining optical fiber I, an electro-optic modulator, a polarization-maintaining optical fiber II, a convex lens III, a wave plate I, a lens table, an atomic force microscope, a probe, a sample, a magnet, a sample table, a signal generator, an oscilloscope, a wave plate II, a convex lens IV and a plane mirror, wherein the magnetization information on the surface of the sample is obtained by adopting a method of interference of two orthogonal polarization components of the same light, the two polarization components share one light path, the separation and the reunion of the light beams are avoided, the two light beams can be relatively easily ensured to be transmitted in the same light path, optical elements in the light path are reduced, so that the signal is less influenced by the movement, the signal-to-noise ratio is improved, and the longitudinal component, the transverse component and the polar component of the Kerr effect are measured by adopting the obliquely incident light beam.
Description
Technical Field
The invention relates to the technical field of physical measurement, in particular to a nanostructure magnetism measurement method for researching magneto-optical Kerr signals of a single nanostructure on the surface of a material by adopting a beam interference method.
Background
The magneto-optical Kerr effect measuring device is an important means in the research of the surface magnetism of materials, the working principle of the magneto-optical Kerr effect measuring device is based on the magneto-optical Kerr effect caused by the interaction between light and a magnetized medium, the magneto-optical Kerr effect measuring device not only can detect the magnetism of a material with a single atomic layer thickness, but also can realize non-contact measurement, and the magneto-optical Kerr effect measuring device has important application in the research of the aspects of the magnetic order, the magnetic anisotropy, the interlayer coupling, the phase change behavior of a magnetic ultrathin film and the like of the magnetic ultrathin. The magneto-optical Kerr effect measuring device is mainly used for carrying out magnetization observation on the surface of a sample by detecting the light intensity change caused by the polarization state change of a beam of linearly polarized light after the linearly polarized light is reflected on the surface of a material. The prior art has the defects that: the spatial resolution of the traditional focusing kerr microscope is determined by the optical diffraction limit, and the imaging effect of the traditional focusing kerr microscope is extremely limited by an optical element, so that the nanometer-scale magnetization dynamic characteristics cannot be obtained. The prior art has the following defects: in some methods for obtaining magnetization information of a sample by measuring interference of two beams of light on a sample surface, light paths of the two beams of light are separately controlled and need to be recombined before detection, so that more optical elements are needed, and a signal-to-noise ratio of an obtained signal is low, which is a third defect in the prior art: in the device for measuring the Kerr rotation of the sample by the interferometry in the prior art, only the polar Kerr effect can be measured, and the nanostructure magnetic measurement method can solve the problem.
Disclosure of Invention
In order to solve the problems, the invention adopts a method of interference of two orthogonal polarization components of the same beam of light to obtain magnetization information of the surface of a sample, the two orthogonal polarization components of the light share one light path, optical elements in the light path are reduced, and the signal to noise ratio is improved; in addition, the invention adopts the atomic force microscope probe with the through hole, and can obtain the magnetization dynamic characteristics of the nanoscale structure on the surface of the sample.
The technical scheme adopted by the invention is as follows:
the measuring device mainly comprises a laser, a beam splitter, a convex lens I, a photoelectric detector, a lock-in amplifier, a prism polarizer, a convex lens II, a polarization-maintaining optical fiber I, an electro-optic modulator, a polarization-maintaining optical fiber II, a convex lens III, a wave plate I, a lens platform, an atomic force microscope, a probe, a sample, a magnet, a sample platform, a signal generator, an oscilloscope, a wave plate II, a convex lens IV and a plane mirror, wherein the wavelength of the laser is adjustable within the range of 400 nanometers to 800 nanometers, xyz is a space rectangular coordinate system, an xy plane is a horizontal plane, a zx plane is vertical to the horizontal plane, the atomic force microscope is positioned below the lens platform, the probe is positioned below the atomic force microscope, the probe is in the shape of a circular table, the diameter of the upper bottom surface of the circular table is 3 micrometers, the diameter of the lower bottom surface of the circular table is 1.5 micrometers, the axial direction of the circular, The magnet and the sample table are sequentially positioned under the probe, the probe is provided with a through hole I and a through hole II, the axes of the through hole I and the through hole II and the axis of the probe circular table are all positioned in a zx plane, the axes of the through hole I and the through hole II are respectively positioned at two sides of the axis of the probe circular table and form an angle of 45 degrees with the axis of the probe circular table, the photoelectric detector is connected with a phase-locked amplifier cable, a signal generator and an oscilloscope are respectively connected with the sample table through cables, the polarization maintaining optical fiber I is provided with a slow axis and a fast axis, a transmission axis of a prism polarizer is parallel to the slow axis of the polarization maintaining optical fiber I, the slow axis of the polarization maintaining optical fiber I is positioned on an angular bisector of an included angle between the transverse magnetic axis and the transverse electric axis of the electro-optical modulator, the transverse magnetic axis of the electro-optical modulator is parallel to the slow axis of the polarization maintaining optical fiber II, the diameters of the through hole I and the, the length of the polarization maintaining optical fiber II is 9 meters, the wave plate I is a half-wave plate, and the wave plate II is a 1/4 wave plate.
Light emitted by the laser sequentially passes through the beam splitter, the prism polarizer, the convex lens II and the polarization maintaining optical fiber I and then enters the electro-optic modulator, two orthogonal polarization components formed by the light in the electro-optic modulator are in-plane polarization and out-of-plane polarization, and the phase phi (t) added to each component is phi0cos (ω t), the phase time difference of the two light components is tau, the light beam enters a polarization maintaining optical fiber II after coming out of the electro-optical modulator, the two orthogonal polarization components of the light are respectively transmitted along the fast axis and the slow axis of the polarization maintaining optical fiber II, the light leaves the polarization maintaining optical fiber II, reaches the surface of a sample through a convex lens III, a wave plate I, a lens platform, an atomic force microscope and a through hole I in sequence and is reflected for the first time, the first reflected light sequentially passes through the through hole II, the atomic force microscope, the lens platform, the lens II and a convex lens IV to reach a plane mirror wave plate and is reflected for the second time, the second reflected light sequentially passes through the convex lens IV, the wave plate II, the lens platform, the atomic force microscope and the through hole II to reach the surface of the sample and is reflected for the third time, the third reflected light sequentially passes through the through hole I, the atomic force microscope, the lens platform, the wave plate I, the convex, The electro-optical modulator, the polarization-maintaining optical fiber I, the convex lens II and the prism polarizer are deflected by the beam splitter and then enter the photoelectric detector through the convex lens I, two polarization components of third reflected light interfere at the photoelectric detector, two orthogonal polarization components of light transmitted along the slow axis and the fast axis of the polarization-maintaining optical fiber II are respectively represented by corresponding Jones matrixes respectively after being output from the polarization-maintaining optical fiber II
And
after passing through the wave plate I, the Jones matrix corresponding to the two orthogonal polarization components of the light is converted into a Jones matrix
And
wherein
Is a phase angle, define
The phase difference of two orthogonal polarization components of the light obtained in the photodetector is expressed as the Jones matrix representing the whole process that the light beam returns to the electro-optic modulator after being reflected twice by the surface of the sample
the phase difference components in the x, y and z directions are respectively alphax、αy、αzCarrying out Fourier analysis on the photocurrent obtained from the photoelectric detector, and obtaining a first-order harmonic component of the photocurrent by the lock-in amplifier:
and second order harmonic components:
taking into account symmetry, αKSimplified to
Where ω is the angular frequency of the time-dependent phase φ (t) of the electro-optic modulator, IincIs the light intensity of the light emitted by the laser, and gamma is the light beam passing through the following optical elements twice: beam splitter, prism polarizer, convex lens II, polarization maintaining fiber I, electrooptical modulator, polarization maintaining fiber II, convex lens III, convex lens IV, and residual proportion of light intensity after being reflected twice by sample surface, J1And J2first and second order are Bessel equations, respectively, alphaKIs a linear equation of the sample magnetization component, m, in the x, y, z directionsx、my、mzfor alphaKIs dependent on
The reflectance of the sample, optical elements in the optical path, etc.
The polar kerr effect corresponds to the z-direction component of the magnetization, the longitudinal kerr effect corresponds to the y-direction component of the magnetization, the transverse kerr effect corresponds to the x-direction component of the magnetization, and the appropriate P should be chosen because the transition of the sample magnetization component is different under different crystallographic symmetry operations1And P2And an optical element in the optical path such that the contribution of the poloidal or longitudinal or transverse magneto-optical kerr effect dominates.
The method for measuring the magnetic property of the nano structure comprises a method for measuring the longitudinal Kerr effect, a method for measuring the polar Kerr effect and a method for measuring the transverse Kerr effect.
The steps of the method for measuring the magnetism of the nano structure are respectively as follows:
method for measuring longitudinal kerr effect:
adjusting the fast axis of the wave plate I to be 22.5 degrees with the y direction, and adjusting the fast axis of the wave plate II to be consistent with the y direction, so that the Jones matrix corresponding to two orthogonal polarization components of incident light after passing through the wave plate I is
Enabling the probe to approach the surface of the sample through an atomic force microscope, scanning the probe within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe upwards by 50 nanometers, and closing the scanning feedback of the atomic force microscope;
adjusting the position of the laser to enable the laser beam emitted by the laser to enter the through hole I of the probe, enabling first reflected light formed after the laser beam is reflected on the surface of the sample to sequentially pass through the through hole II of the probe, the wave plate II and the convex lens IV to reach the plane mirror, and enabling the first reflected light to be reflected by the plane mirror to form second reflected light;
fifthly, adjusting the positions of the convex lens IV and the plane mirror to enable the second reflected light to be emitted to the surface of the sample through the through hole II of the probe and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe, the atomic force microscope, the lens platform, the wave plate I, the convex lens III, the polarization maintaining optical fiber II, the electro-optic modulator, the polarization maintaining optical fiber I, the convex lens II and the prism polarizer, is deflected by the beam splitter and enters the photoelectric detector through the convex lens I, and two polarization components of the light beam interfere at the photoelectric detector;
outputting the signal from the photoelectric detector to a phase-locked amplifier for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity is a first-order harmonic component
Longitudinal kerr rotation
rpAnd rsThe reflectivities of the P polarized light and the S polarized light on the surface of the sample are respectively;
eight is formed by
The kerr rotation is calculated.
Method for measuring polar kerr effect:
adjusting the fast axis of the wave plate I to be 22.5 degrees with the y direction, and adjusting the fast axis of the wave plate II to be consistent with the y direction, so that the Jones matrix corresponding to two orthogonal polarization components of incident light after passing through the wave plate I is
Enabling the probe to approach the surface of the sample through an atomic force microscope, scanning the probe within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe upwards by 50 nanometers, and closing the scanning feedback of the atomic force microscope;
adjusting the position of the laser to enable the laser beam emitted by the laser to enter the through hole I of the probe, enabling first reflected light formed after the laser beam is reflected on the surface of the sample to sequentially pass through the through hole II of the probe, the wave plate II and the convex lens IV to reach the plane mirror, and enabling the first reflected light to be reflected by the plane mirror to form second reflected light;
fifthly, adjusting the positions of the convex lens IV and the plane mirror to enable the second reflected light to be emitted to the surface of the sample through the through hole II of the probe and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe, the atomic force microscope, the lens platform, the wave plate I, the convex lens III, the polarization maintaining optical fiber II, the electro-optic modulator, the polarization maintaining optical fiber I, the convex lens II and the prism polarizer, is deflected by the beam splitter and enters the photoelectric detector through the convex lens I, and two polarization components of the light beam interfere at the photoelectric detector;
outputting the signal from the photoelectric detector to a phase-locked amplifier for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity is a first-order harmonic component
Polar kerr rotation
rpAnd rsThe reflectivities of the P-polarized light and the S-polarized light respectively at the sample surface,
eight is formed by
The kerr rotation is calculated.
Method for measuring transverse kerr effect:
removing the wave plate I, and adjusting the fast axis of the wave plate II to form 45 degrees with the y direction, so that after passing through the wave plate I, two orthogonal polarizations of incident light are formedThe Jones matrix corresponding to the vibration component is
And
enabling the probe to approach the surface of the sample through an atomic force microscope, scanning the probe within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe upwards by 50 nanometers, and closing the scanning feedback of the atomic force microscope;
adjusting the position of the laser to enable the laser beam emitted by the laser to enter the through hole I of the probe, enabling first reflected light formed after the laser beam is reflected on the surface of the sample to sequentially pass through the through hole II of the probe, the wave plate II and the convex lens IV to reach the plane mirror, and enabling the first reflected light to be reflected by the plane mirror to form second reflected light;
fifthly, adjusting the positions of the convex lens IV and the plane mirror to enable the second reflected light to be emitted to the surface of the sample through the through hole II of the probe and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe, the atomic force microscope, the lens platform, the wave plate I, the convex lens III, the polarization maintaining optical fiber II, the electro-optic modulator, the polarization maintaining optical fiber I, the convex lens II and the prism polarizer, is deflected by the beam splitter and enters the photoelectric detector through the convex lens I, and two polarization components of the light beam interfere at the photoelectric detector;
outputting the signal from the photoelectric detector to a phase-locked amplifier for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity is a first-order harmonic component
Transverse kerr rotation
rpAnd rsThe reflectivities of the P polarized light and the S polarized light on the surface of the sample are respectively;
eight is formed by
The kerr rotation is calculated.
The invention has the beneficial effects that:
in the Kerr rotation of a sample measured by an interference method in the prior art, an interference loop of a light path has a certain area, and the interference measurement is carried out by replacing two independent light beams with two orthogonal polarization components of the same light beam, so that the method has the advantages that: it is relatively easy to ensure that both beams travel the same path by avoiding beam splitting and re-integration, so that the signal is less affected by the sample and by the movement of the optical elements in the interference loop.
Drawings
The following is further illustrated in connection with the figures of the present invention:
FIG. 1 is a schematic of the present invention.
In the figure, 1, a laser, 2, a beam splitter, 3, a convex lens I, 4, a photoelectric detector, 5, a phase-locked amplifier, 6, a prism polarizer, 7, a convex lens II, 8, a polarization-maintaining optical fiber I, 9, an electro-optical modulator, 10, a polarization-maintaining optical fiber II, 11, a convex lens III, 12, a wave plate I, 13, a lens table, 14, an atomic force microscope, 15, a probe, 16, a sample, 17, a magnet, 18, a sample table, 19, a signal generator, 20, an oscilloscope, 21, a wave plate II, 22, a convex lens IV, 23 and a plane mirror.
Detailed Description
As shown in fig. 1, the left lower corner has an xyz three-dimensional direction indicator, xyz is a spatial rectangular coordinate system, xy plane is a horizontal plane, zx plane is perpendicular to the horizontal plane, the measuring apparatus mainly includes a laser 1, a beam splitter 2, a convex lens I3, a photodetector 4, a lock-in amplifier 5, a prism polarizer 6, a convex lens II7, a polarization maintaining fiber I8, an electro-optic modulator 9, a polarization maintaining fiber II10, a convex lens III11, a wave plate I12, a lens stage 13, an atomic force microscope 14, a probe 15, a sample 16, a magnet 17, a sample stage 18, a signal generator 19, an oscilloscope 20, a wave plate II21, a convex lens IV22, and a plane mirror 23, the wavelength of the laser 1 is adjustable in the range of 400 nm to 800 nm, the atomic force microscope 14 is located below the lens stage 13, the probe 15 is located below the atomic force microscope 14, the probe 15 is an atomic force microscope probe and is in the shape of a circular truncated cone, the diameter of the upper bottom surface of the circular truncated cone is 3 micrometers, the diameter of the lower bottom surface of the circular truncated cone is 1.5 micrometers, the axial direction of the circular truncated cone is vertical to the horizontal plane, a sample 16, a magnet 17 and a sample table 18 are sequentially positioned under a probe 15, a through hole I and a through hole II are arranged in the probe 15, the axes of the through hole I and the through hole II and the axis of the circular truncated cone of the probe 15 are all positioned in a zx plane, the axes of the through hole I and the through hole II are respectively positioned on two sides of the axial line of the circular truncated cone of the probe 15 and form an angle of 45 degrees with the axial line of the circular truncated cone of the probe 15, a photoelectric detector 4 is in cable connection with a phase-locked amplifier 5, a signal generator 19 and an oscilloscope 20 are respectively in cable connection with the sample table 18, a polarization maintaining optical fiber I8 is provided with a slow axis and a fast axis, a transmission axis of a prism polarizer 6 is parallel to the slow axis of a polarization maintaining optical fiber I36, the transverse magnetic axis of the electro-optical modulator 9 is parallel to the slow axis of the polarization maintaining fiber II10, the diameters of the through hole I and the through hole II in the probe 15 are both 200 nanometers, the length of the polarization maintaining fiber I8 is 2 meters, the length of the polarization maintaining fiber II10 is 9 meters, the wave plate I12 is a half-wave plate, and the wave plate II21 is a 1/4 wave plate.
The light emitted by the laser 1 sequentially passes through the beam splitter 2, the prism polarizer 6, the convex lens II7 and the polarization maintaining optical fiber I8 and then enters the electro-optical modulator 9, the light forms two orthogonal polarization components in the electro-optical modulator 9, the two orthogonal polarization components are in-plane polarization and out-of-plane polarization, and the phase phi (t) added to each component is phi (t) ═ phi0cos (ω t), the phase time difference of the two light components is τ, the light beam enters the polarization maintaining fiber II10 after coming out of the electro-optical modulator 9, the two orthogonal polarization components of the light are respectively transmitted along the fast axis and the slow axis of the polarization maintaining fiber II10, the light leaves the polarization maintaining fiber II10, reaches the surface of the sample 16 through the convex lens III11, the wave plate I12, the lens stage 13, the atomic force microscope 14 and the through hole I in sequence, is reflected for the first time, the first reflected light reaches the plane mirror 23 through the through hole II, the atomic force microscope 14, the lens stage 13, the wave plate II21 and the convex lens IV22 in sequence, is reflected for the second time, and the second reflected light reaches the surface of the sample through the convex lens IV22, the wave plate II21, the lens stage 13, the atomic force microscope 14 and the through hole II in sequenceAnd is reflected by the surface of the sample 16 for the third time, the third reflected light sequentially passes through the through hole I, the atomic force microscope 14, the lens table 13, the wave plate I12, the convex lens III11, the polarization-maintaining fiber II10, the electro-optic modulator 9, the polarization-maintaining fiber I8, the convex lens II7 and the prism polarizer 6, is deflected by the beam splitter 2, and enters the photoelectric detector 4 through the convex lens I3, two polarization components of the third reflected light interfere at the photoelectric detector 4, two orthogonal polarization components of light transmitted along the slow axis and the fast axis of the polarization-maintaining fiber II10 respectively, and corresponding Jones matrixes output from the polarization-maintaining fiber II10 are respectively represented as Jones matrixes respectively
And
after passing through a wave plate I12, the Jones matrix corresponding to two orthogonal polarization components of the light is converted into a matrix
And
wherein
Is a phase angle, define
The phase difference of the two orthogonal polarization components of the light obtained in the photodetector 4 is represented as the Jones matrix representing the entire process of the light beam returning to the electro-optical modulator 9 after two reflections from the sample surface
the phase difference components in the x, y and z directions are respectively alphax、αy、αzFourier-dividing the photocurrent obtained in the photodetector 4The lock-in amplifier 5 obtains the first harmonic component of the photocurrent:
and second order harmonic components:
taking into account symmetry, αKSimplified to
Where ω is the angular frequency, I, of the time-dependent phase φ (t) of the electro-optical modulator 9incIs the light intensity of the light emitted by the laser, and gamma is the light beam passing through the following optical elements twice: beam splitter 2, prism polarizer 6, convex lens II7, polarization maintaining fiber I8, electro-optic modulator 9, polarization maintaining fiber II10, convex lens III11, and convex lens IV22, and the residual proportion of light intensity after being reflected twice by the surface of sample 16, J1And J2first and second order are Bessel equations, respectively, alphaKIs a linear equation of the sample magnetization component, m, in the x, y, z directionsx、my、mzfor alphaKIs dependent on
The reflectance of the sample, optical elements in the optical path, etc.
The polar kerr effect corresponds to the z-direction component of the magnetization, the longitudinal kerr effect corresponds to the y-direction component of the magnetization, the transverse kerr effect corresponds to the x-direction component of the magnetization, and the appropriate P should be chosen because the transition of the sample magnetization component is different under different crystallographic symmetry operations1And P2And an optical element in the optical path such that the contribution of the poloidal or longitudinal or transverse magneto-optical kerr effect dominates.
The method for measuring the magnetic property of the nano structure comprises a method for measuring the longitudinal Kerr effect, a method for measuring the polar Kerr effect and a method for measuring the transverse Kerr effect.
The method for measuring the magnetism of the nano structure comprises the following steps:
method for measuring longitudinal kerr effect:
the fast axis of the adjusting wave plate I12 is 22.5 degrees with the y direction, and the fast axis of the adjusting wave plate II21 is consistent with the y direction, so that after passing through the wave plate I12, two orthogonal polarization components of incident light correspond to Jones matrix of Jones
Secondly, enabling the probe 15 to approach the surface of the sample 16 through the atomic force microscope 14, enabling the probe 15 to scan within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe 15 upwards by a distance of 50 nanometers, and closing the scanning feedback of the atomic force microscope 14;
fourthly, adjusting the position of the laser 1 to enable the laser beam emitted by the laser 1 to enter the through hole I of the probe 15, enabling first reflected light formed by the laser beam after being reflected on the surface of the sample 16 to sequentially pass through the through hole II of the probe 15, the wave plate II21 and the convex lens IV22 to reach the plane mirror 23, and being reflected by the plane mirror 23 to form second reflected light;
fifthly, adjusting the positions of the convex lens IV22 and the plane mirror 23 to enable the second reflected light to be emitted to the surface of the sample 16 through the through hole II of the probe 15 and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe 15, the atomic force microscope 14, the lens table 13, the wave plate I12, the convex lens III11, the polarization maintaining optical fiber II10, the electro-optical modulator 9, the polarization maintaining optical fiber I8, the convex lens II7 and the prism polarizer 6, is deflected by the beam splitter 2 and enters the photoelectric detector 4 through the convex lens I3, and two polarization components of the light beam interfere at the photoelectric detector 4;
outputting the signal from the photoelectric detector 4 to the phase-locked amplifier 5 for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity first-order harmonic component
Longitudinal kerr rotation
rpAnd rsThe reflectivities of the P polarized light and the S polarized light on the surface of the sample are respectively;
eight is formed by
The kerr rotation is calculated.
Method for measuring polar kerr effect:
the fast axis of the adjusting wave plate I12 is 22.5 degrees with the y direction, and the fast axis of the adjusting wave plate II21 is consistent with the y direction, so that after passing through the wave plate I12, two orthogonal polarization components of incident light correspond to Jones matrix of Jones
Secondly, enabling the probe 15 to approach the surface of the sample 16 through the atomic force microscope 14, enabling the probe 15 to scan within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe 15 upwards by a distance of 50 nanometers, and closing the scanning feedback of the atomic force microscope 14;
fourthly, adjusting the position of the laser 1 to enable the laser beam emitted by the laser 1 to enter the through hole I of the probe 15, enabling first reflected light formed by the laser beam after being reflected on the surface of the sample 16 to sequentially pass through the through hole II of the probe 15, the wave plate II21 and the convex lens IV22 to reach the plane mirror 23, and being reflected by the plane mirror 23 to form second reflected light;
fifthly, adjusting the positions of the convex lens IV22 and the plane mirror 23 to enable the second reflected light to be emitted to the surface of the sample 16 through the through hole II of the probe 15 and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe 15, the atomic force microscope 14, the lens table 13, the wave plate I12, the convex lens III11, the polarization maintaining optical fiber II10, the electro-optical modulator 9, the polarization maintaining optical fiber I8, the convex lens II7 and the prism polarizer 6, is deflected by the beam splitter 2 and enters the photoelectric detector 4 through the convex lens I3, and two polarization components of the light beam interfere at the photoelectric detector 4;
outputting the signal from the photoelectric detector 4 to the phase-locked amplifier 5 for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity first-order harmonic component
Polar kerr rotation
rpAnd rsThe reflectivity of the sample surface for p-polarized light and s-polarized light respectively,
eight is formed by
The kerr rotation is calculated.
Method for measuring transverse kerr effect:
removing the wave plate I12, and adjusting the fast axis of the wave plate II21 to be 45 degrees with the y direction, so that after passing through the wave plate I12, the Jones matrix corresponding to two orthogonal polarization components of the incident light is
And
secondly, enabling the probe 15 to approach the surface of the sample 16 through the atomic force microscope 14, enabling the probe 15 to scan within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe 15 upwards by a distance of 50 nanometers, and closing the scanning feedback of the atomic force microscope 14;
fourthly, adjusting the position of the laser 1 to enable the laser beam emitted by the laser 1 to enter the through hole I of the probe 15, enabling first reflected light formed by the laser beam after being reflected on the surface of the sample 16 to sequentially pass through the through hole II of the probe 15, the wave plate II21 and the convex lens IV22 to reach the plane mirror 23, and being reflected by the plane mirror 23 to form second reflected light;
fifthly, adjusting the positions of the convex lens IV22 and the plane mirror 23 to enable the second reflected light to be emitted to the surface of the sample 16 through the through hole II of the probe 15 and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe 15, the atomic force microscope 14, the lens table 13, the wave plate I12, the convex lens III11, the polarization maintaining optical fiber II10, the electro-optical modulator 9, the polarization maintaining optical fiber I8, the convex lens II7 and the prism polarizer 6, is deflected by the beam splitter 2 and enters the photoelectric detector 4 through the convex lens I3, and two polarization components of the light beam interfere at the photoelectric detector 4;
outputting the signal from the photoelectric detector 4 to the phase-locked amplifier 5 for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity first-order harmonic component
Transverse kerr rotation
rpAnd rsThe reflectivities of the p-polarized light and the s-polarized light on the surface of the sample are respectively;
eight is formed by
The kerr rotation is calculated.
The invention adopts an atomic force microscope probe with a through hole to obtain the magnetization information of a nanoscale structure on the surface of a sample, and secondly, the invention adopts a method of interference of two orthogonal polarization components of the same light to obtain the magnetization information on the surface of the sample, the two polarization components share one light path to avoid the separation and the reunion of the light beams, so that the two light beams can be relatively easily ensured to be transmitted in the same light path, and optical elements in the light path are reduced, so that the signal is less influenced by the movement of the sample and the optical elements in an interference loop, the signal to noise ratio is improved, and in addition, the longitudinal component, the transverse component and the polar component of the Kerr effect can be measured without greatly changing the light path in a device by adopting the obliquely incident light beams.
Claims (1)
1. A nanostructure magnetism measuring method is disclosed, the measuring device mainly comprises a laser, a beam splitter, a convex lens I, a photoelectric detector, a lock-in amplifier, a prism polarizer, a convex lens II, a polarization maintaining optical fiber I, an electro-optic modulator, a polarization maintaining optical fiber II, a convex lens III, a wave plate I, a lens platform, an atomic force microscope, a probe, a sample, a magnet, a sample platform, a signal generator, an oscilloscope, a wave plate II, a convex lens IV and a plane mirror, the wavelength of the laser is adjustable within the range of 400 nm to 800 nm, xyz is a space rectangular coordinate system, an xy plane is a horizontal plane, a zx plane is vertical to the horizontal plane, the atomic force microscope is positioned below the lens platform, the probe is positioned below the atomic force microscope, the probe is an atomic force microscope probe and is in the shape of a circular table, the diameter of the upper bottom surface of the circular table is 3 microns, the diameter of the lower bottom surface of the circular table is 1.5 microns, the sample, the magnet and the sample platform are sequentially positioned under the probe, the probe is provided with a through hole I and a through hole II, the axes of the through hole I and the through hole II and the axis of the probe circular truncated cone are positioned in a zx plane, the axes of the through hole I and the through hole II are respectively positioned at two sides of the axis of the probe circular truncated cone and form an angle of 45 degrees with the axis of the probe circular truncated cone, the photoelectric detector is connected with a phase-locked amplifier cable, the signal generator and the oscilloscope are respectively connected with the sample platform through cables, the polarization maintaining optical fiber I is provided with a slow axis and a fast axis, the transmission axis of the prism polarizer is parallel to the slow axis of the polarization maintaining optical fiber I, the slow axis of the polarization maintaining optical fiber I is positioned on an angular bisector of an included angle between the transverse magnetic axis and the transverse electric axis of the electro-optical modulator, the transverse magnetic axis of the electro-optical modulator is parallel to the slow axis of the polarization maintaining optical fiber II, the diameters of the through hole, the length of the polarization maintaining optical fiber II is 9 meters, the wave plate I is a half-wave plate, the wave plate II is a 1/4 wave plate, light emitted by the laser sequentially passes through the beam splitter, the prism polarizer, the convex lens II and the polarization maintaining optical fiber I and then enters the electro-optic modulator, and the light is shaped in the electro-optic modulatorThe two orthogonal polarization components are in-plane and out-of-plane, and each component plus a phase phi (t) phi0cos (ω t), the phase time difference of the two light components is tau, the light beam enters a polarization maintaining optical fiber II after coming out of the electro-optical modulator, the two orthogonal polarization components of the light are respectively transmitted along the fast axis and the slow axis of the polarization maintaining optical fiber II, the light leaves the polarization maintaining optical fiber II, reaches the surface of a sample through a convex lens III, a wave plate I, a lens platform, an atomic force microscope and a through hole I in sequence and is reflected for the first time, the first reflected light sequentially passes through the through hole II, the atomic force microscope, the lens platform, the lens II and a convex lens IV to reach a plane mirror wave plate and is reflected for the second time, the second reflected light sequentially passes through the convex lens IV, the wave plate II, the lens platform, the atomic force microscope and the through hole II to reach the surface of the sample and is reflected for the third time, the third reflected light sequentially passes through the through hole I, the atomic force microscope, the lens platform, the wave plate I, the convex, The electro-optical modulator, the polarization-maintaining optical fiber I, the convex lens II and the prism polarizer are deflected by the beam splitter and then enter the photoelectric detector through the convex lens I, two polarization components of third reflected light interfere at the photoelectric detector, two orthogonal polarization components of light transmitted along the slow axis and the fast axis of the polarization-maintaining optical fiber II are respectively represented by corresponding Jones matrixes respectively after being output from the polarization-maintaining optical fiber II
And
after passing through the wave plate I, the Jones matrix corresponding to the two orthogonal polarization components of the light is converted into a Jones matrix
And
which is composed of
Is a phase angleDefinition of
The phase difference of two orthogonal polarization components of the light obtained in the photodetector is expressed as the Jones matrix representing the whole process that the light beam returns to the electro-optic modulator after being reflected twice by the surface of the sample
the phase difference components in the x, y and z directions are respectively alphax、αy、αzCarrying out Fourier analysis on the photocurrent obtained from the photoelectric detector, and obtaining a first-order harmonic component of the photocurrent by the lock-in amplifier:
and second order harmonic components:
taking into account symmetry, αKSimplified to
Where ω is the angular frequency of the time-dependent phase φ (t) of the electro-optic modulator, IincIs the light intensity of the light emitted by the laser, and gamma is the light beam passing through the following optical elements twice: beam splitter, prism polarizer, convex lens II, polarization maintaining fiber I, electrooptical modulator, polarization maintaining fiber II, convex lens III, convex lens IV, and residual proportion of light intensity after being reflected twice by sample surface, J1And J2first and second order are Bessel equations, respectively, alphaKIs a linear equation of the sample magnetization component, m, in the x, y, z directionsx、my、mzfor alphaKIs dependent on
The reflection coefficient of the sample, the optical elements in the optical path,
the method is characterized by comprising the following steps:
method for measuring longitudinal kerr effect:
adjusting the fast axis of the wave plate I to be 22.5 degrees with the y direction, and adjusting the fast axis of the wave plate II to be consistent with the y direction, so that the Jones matrix corresponding to two orthogonal polarization components of incident light after passing through the wave plate I is
Enabling the probe to approach the surface of the sample through an atomic force microscope, scanning the probe within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe upwards by 50 nanometers, and closing the scanning feedback of the atomic force microscope;
adjusting the position of the laser to enable the laser beam emitted by the laser to enter the through hole I of the probe, enabling first reflected light formed after the laser beam is reflected on the surface of the sample to sequentially pass through the through hole II of the probe, the wave plate II and the convex lens IV to reach the plane mirror, and enabling the first reflected light to be reflected by the plane mirror to form second reflected light;
fifthly, adjusting the positions of the convex lens IV and the plane mirror to enable the second reflected light to be emitted to the surface of the sample through the through hole II of the probe and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe, the atomic force microscope, the lens platform, the wave plate I, the convex lens III, the polarization maintaining optical fiber II, the electro-optic modulator, the polarization maintaining optical fiber I, the convex lens II and the prism polarizer, is deflected by the beam splitter and enters the photoelectric detector through the convex lens I, and two polarization components of the light beam interfere at the photoelectric detector;
outputting the signal from the photoelectric detector to a phase-locked amplifier for Fourier analysis to obtain a differencePhase division, under which condition the light intensity first order harmonic component
Longitudinal kerr rotation
rpAnd rsThe reflectivities of the P polarized light and the S polarized light on the surface of the sample are respectively;
eight is formed by
Calculating to obtain Kerr rotation;
method for measuring polar kerr effect:
adjusting the fast axis of the wave plate I to be 22.5 degrees with the y direction, and adjusting the fast axis of the wave plate II to be consistent with the y direction, so that the Jones matrix corresponding to two orthogonal polarization components of incident light after passing through the wave plate I is
Enabling the probe to approach the surface of the sample through an atomic force microscope, scanning the probe within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe upwards by 50 nanometers, and closing the scanning feedback of the atomic force microscope;
adjusting the position of the laser to enable the laser beam emitted by the laser to enter the through hole I of the probe, enabling first reflected light formed after the laser beam is reflected on the surface of the sample to sequentially pass through the through hole II of the probe, the wave plate II and the convex lens IV to reach the plane mirror, and enabling the first reflected light to be reflected by the plane mirror to form second reflected light;
fifthly, adjusting the positions of the convex lens IV and the plane mirror to enable the second reflected light to be emitted to the surface of the sample through the through hole II of the probe and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe, the atomic force microscope, the lens platform, the wave plate I, the convex lens III, the polarization maintaining optical fiber II, the electro-optic modulator, the polarization maintaining optical fiber I, the convex lens II and the prism polarizer, is deflected by the beam splitter and enters the photoelectric detector through the convex lens I, and two polarization components of the light beam interfere at the photoelectric detector;
outputting the signal from the photoelectric detector to a phase-locked amplifier for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity is a first-order harmonic component
Polar kerr rotation
rpAnd rsThe reflectivities of the P-polarized light and the S-polarized light respectively at the sample surface,
eight is formed by
Calculating to obtain Kerr rotation;
method for measuring transverse kerr effect:
removing the wave plate I, and adjusting the fast axis of the wave plate II to form 45 degrees with the y direction, so that after passing through the wave plate I, the Jones matrix corresponding to two orthogonal polarization components of incident light is
And
enabling the probe to approach the surface of the sample through an atomic force microscope, scanning the probe within a range of two micrometers at a scanning speed of 2 nanometers/second, and determining the edge position of the sample through the surface profile of the sample obtained in the scanning;
retracting the probe upwards by 50 nanometers, and closing the scanning feedback of the atomic force microscope;
adjusting the position of the laser to enable the laser beam emitted by the laser to enter the through hole I of the probe, enabling first reflected light formed after the laser beam is reflected on the surface of the sample to sequentially pass through the through hole II of the probe, the wave plate II and the convex lens IV to reach the plane mirror, and enabling the first reflected light to be reflected by the plane mirror to form second reflected light;
fifthly, adjusting the positions of the convex lens IV and the plane mirror to enable the second reflected light to be emitted to the surface of the sample through the through hole II of the probe and form third reflected light;
the third reflected light sequentially passes through the through hole I of the probe, the atomic force microscope, the lens platform, the wave plate I, the convex lens III, the polarization maintaining optical fiber II, the electro-optic modulator, the polarization maintaining optical fiber I, the convex lens II and the prism polarizer, is deflected by the beam splitter and enters the photoelectric detector through the convex lens I, and two polarization components of the light beam interfere at the photoelectric detector;
outputting the signal from the photoelectric detector to a phase-locked amplifier for Fourier analysis to obtain a differential phase, wherein under the condition, the light intensity is a first-order harmonic component
Transverse kerr rotation
rpAnd rsThe reflectivities of the P polarized light and the S polarized light on the surface of the sample are respectively;
eight is formed by
The kerr rotation is calculated.
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