CN114839009B - A device and method for detwinning of layered single crystal samples - Google Patents

Abstract

The invention provides a device and method for detwinning of a layered single crystal sample. The device comprises: a metal outer frame with an inner cavity; and a metal sheet located in the inner cavity of the metal outer frame; two of the metal sheet The end is fixed to the metal frame; the thermal expansion coefficient of the metal frame is smaller than that of the metal sheet; the metal sheet is configured to carry and fix the sample. Difference, the metal sheet is under tension and transfers the tensile strain to the sample. The device can not only realize detwinning of single crystal samples, but also transfer the remaining uniaxial strain to single crystal samples, so that the samples have a certain uniaxial strain on the basis of detwinning.

Description

A device and method for detwinning of layered single crystal samples

technical field

The invention relates to the technical field of metallographic microanalysis. More specifically, it relates to a device and method for detwinning a layered single crystal sample.

Background technique

For most iron-based superconductors, as the temperature decreases, the system will undergo a structural phase transition from tetragonal phase (a _T ＝ b _T ) to orthorhombic phase (orthorhombic phase, a _o >b _o ) (T<T _S ), the angle between the two unit cell base vectors is 45°. Studies have shown that after the structural phase transition, two sets of symmetrical twin domain structures are formed in the iron-based superconductor, and the domains are parallel to each other in regular stripes along the (100) and (010) directions of the tetragonal phase in the ab plane of the sample. Or vertical arrangement; along the c direction, it can extend to the entire sample without being affected by surface defects of the sample; if the sample quality is high, the twin domain walls are smooth and regular, with a spacing of about 10 microns, as shown in Figure 1 and Figure 2 shown.

In iron-based superconductors, the origin of physical phenomena such as superconductivity and resistance anisotropy still lacks a unified theoretical explanation. However, the existence of twinning hinders researchers from studying the properties of the system such as intrinsic magnetism and electrical resistance ^[2-3] . For example, the existence of twinning causes T< _TS to have both (020) _o and (200) _o contributions at the position of the structural peak (020) _o . In the experiment, it is particularly important to research and develop more mature detwinning methods. At present, the detwinning process of large (centimeter-scale) bulk single crystal samples by applying uniaxial mechanical stress is relatively mature, but it is accompanied by a huge background signal from the detwinning device. However, there is still a lack of relatively mature methods for detwinning small (millimeter-scale) layered single crystal samples in experimental research.

Taking the layered single crystal sample of Fe-based superconductor, FeSe (T _S =90K) as an example, the basic size of the sample is 2*2*0.05mm ³ . Researchers have used different experimental methods to study the magnetic properties, electrical resistance and other information of twinned FeSe single crystals. However, limited by the development of detwinning technology, the intrinsic physical properties of FeSe single crystals need to be further studied. Based on this, we invented and designed a new device for detwinning of layered single crystal samples, and verified the practicability and feasibility of the device by various experimental methods.

Contents of the invention

In view of the above problems, the present invention provides a device for detwinning of layered single crystal samples to solve the problem that traditional mechanical pressing methods cannot be used to detwinn the layered single crystal samples with a smaller size (millimeter order) question.

To achieve the above object, the present invention adopts the following technical solutions:

The invention provides a device for detwinning a layered single crystal sample, comprising:

a metal frame with an internal cavity; and

a metal sheet located in the inner cavity of the metal frame;

The two ends of the metal sheet are fixed to the metal frame;

The thermal expansion coefficient of the metal frame is smaller than that of the metal sheet;

The metal sheet is configured to carry and fix the sample. In a low temperature environment, due to the difference in thermal expansion coefficient between the metal frame and the metal sheet, the metal sheet is subjected to tension and transmits tensile strain to the sample.

In addition, it is preferred that the metal sheet includes a middle area, two transition areas located at both ends of the middle area, and two transition areas respectively formed at the ends of the two transition areas away from the middle area to be combined and fixed with the metal frame. fixed area;

The two sides of the transition zone gradually narrow toward the middle zone.

In addition, preferably, the connection between the intermediate region and the transition region and the connection between the transition region and the fixed region both include arc-shaped transition portions.

In addition, the preferred solution is that the two sides of the middle area are straight sides;

The two sides of the transition zone are sloped sides that gradually converge.

In addition, the preferred solution is to define that the length direction of the metal frame is the first direction, the width direction of the metal frame is the second direction, and the height direction of the metal frame is the third direction;

The metal sheet is arranged along the first direction;

The size of the metal frame in the first direction is 95mm, the size of the metal frame in the second direction is 45mm, and the size of the metal frame in the third direction is 5mm;

The size of the middle zone in the first direction is 20mm, the size of the middle zone in the second direction is 15mm, and the size of the middle zone in the third direction is 0.2mm;

The size of the fixing area in the first direction is 7 mm, the size of the fixing area in the second direction is 35 mm, and the size of the fixing area in the third direction is 0.2 mm.

In addition, preferably, the device further includes a connection part formed on the metal outer frame for connecting with external equipment.

In addition, preferably, the metal frame is made of Invar alloy; the metal sheet is made of 6061 aluminum alloy.

In addition, it is preferred that the device includes two clamping fixtures arranged at both ends of the metal sheet and fixed to the metal frame, the metal sheet is located between the two clamping fixtures; the two clamping fixtures It is configured to clamp and fix the sheet metal within the metal frame.

The present invention also provides a method for detwinning a layered single crystal sample, the method comprising:

Fix both ends of the metal sheet to the metal frame;

Fix the layered single crystal sample on the metal sheet;

In a low temperature environment, since the thermal expansion coefficient of the metal frame is smaller than that of the metal sheet, the metal sheet is subjected to tension and transmits the tensile strain to the sample;

Analyze the samples;

The analysis includes anisotropic resistivity testing or elastic neutron diffraction measurements.

In addition, a preferred solution is that both ends of the metal sheet are fixed in the metal outer frame by clamping and fixing parts, and the method further includes:

Apply STYCAST 2850FT glue evenly on the contact position between the metal sheet, the clamping fixture and the metal frame, and bake it at 65°C for 2 hours.

The beneficial effects of the present invention are:

The present invention can be widely applied to a variety of layered single crystal samples. The device can not only realize detwinning of single crystal samples, but also transfer the remaining uniaxial strain to single crystal samples, so that the samples have A certain uniaxial strain.

In the experimental research, on the one hand, the improvement of the detwinning technology is beneficial to the study of the intrinsic properties of the sample and enhances the understanding of the research system; on the other hand, the introduction of uniaxial strain in the system may induce some novel physical phenomena Or cause changes in order parameters.

Description of drawings

The specific implementation manners of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Fig. 1 is an optical image of single crystal domain structure of CaFe ₂ As ₂ single crystal (T _S =173K) at 293K and 5K.

Figure 2 shows that in the BaFe ₂ As ₂ single crystal, when T< _TS (138K), the tetragonal phase lattice undergoes a structural phase transition into the orthorhombic phase and forms two sets of twin crystal domains.

Fig. 3 is a schematic diagram of the overall structure of the present invention.

Fig. 4 is a schematic structural view of the metal sheet of the present invention.

Fig. 5 is the cooperation diagram of the present invention and a single sample.

Figure 6 is an anisotropic resistivity measurement of a detwinned FeSe single crystal and characterization of the uniaxial strain of the device.

Fig. 7 is a diagram of cooperation between the present invention and several samples.

Figure 8 is the neutron diffraction result of the structural peak (020) of detwinned FeSe (tighten the top screw) and the neutron diffraction result of the structural peak (020) of twinned FeSe (loosen the top screw).

Detailed ways

Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the relative arrangements of components and steps, numerical expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise.

The following description of at least one exemplary embodiment is merely illustrative in nature and in no way taken as limiting the invention, its application or uses.

Techniques and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such techniques and devices should be considered part of the description.

In all examples shown and discussed herein, any specific values should be construed as exemplary only, and not as limitations. Therefore, other instances of the exemplary embodiment may have different values.

It should be noted that like numerals and letters denote like items in the following figures, therefore, once an item is defined in one figure, it does not require further discussion in subsequent figures.

The existing traditional mechanical pressing method is to directly transfer the stress to the centimeter-sized single crystal sample by rotating the screw, so it is impossible to directly transfer the stress to the millimeter-sized single crystal sample.

In addition, the traditional mechanical pressing method requires the sample to have a certain hardness, and the layered soft sample cannot withstand this pressing method.

In order to solve the problem that the traditional mechanical pressing method cannot detwin the layered single crystal sample whose size is on the order of millimeters. The present invention provides a device for detwinning of layered single crystal samples, as shown in Figures 1 to 8, specifically the device for detwinning of layered single crystal samples includes: a metal with an inner cavity The outer frame 1; and the metal sheet 2 located in the inner cavity of the metal outer frame 1; the two ends of the metal sheet 2 are fixed to the metal outer frame 1; the thermal expansion coefficient of the metal outer frame 1 is smaller than that of the metal sheet 2; The metal sheet 2 is configured to carry and fix the sample 3. In a low temperature environment, due to the difference in thermal expansion coefficient between the metal frame 1 and the metal sheet 2, the metal sheet 2 is subjected to tension and transmits tensile strain to the sample 3 through glue . The device can be widely used in detwinning of various layered single crystal samples and can apply uniaxial strain to the samples, successfully solving the technical problem of detwinning of layered samples with small size in iron-based superconductors, which is conducive to research Researchers have used a variety of experimental methods to probe the intrinsic properties of these systems, thereby enhancing the understanding of the interaction of various order parameters in the system; for layered single crystal samples without twinning effect, the device can apply along the Uniaxial strain in a specific direction may induce new physical phenomena or regulate ordered parameters.

The design idea for the device comes from the difference in the thermal expansion coefficients of different metals. The metal frame 1 is made of Invar alloy, and its thermal expansion coefficient is about 2×10 ^-6 /K; the metal sheet 2 is made of 6061 aluminum alloy, and its thermal expansion coefficient is about 24×10 ^-6 /K. As the temperature decreases, due to the difference in thermal expansion coefficient between the Invar alloy frame and the 0.2 mm thick 6061 aluminum alloy sheet with the sample attached, the Invar alloy frame shrinks slowly, and the inner 6061 aluminum alloy sheet shrinks faster, while the aluminum alloy sheet shrinks faster. The alloy sheet is connected to the Invar alloy frame through STYCAST 2850FT glue and screws, resulting in the aluminum alloy sheet being stretched along the length of the metal frame at low temperature. The aluminum alloy sheet is designed as a specific shape with wider ends and narrower middle. During the cooling process, the uniaxial strain [~22*(300-T)×10 ^-6 ] converges in the middle of the aluminum alloy sheet more uniformly and intensively. narrower area. Through the action of specific glue, the strain is transmitted to multiple single crystal samples at the same time, so that large-area layered single crystal samples can be simultaneously de-twinned or regulated by uniaxial strain.

In one embodiment, with regard to the specific structure of the metal sheet 2, the metal sheet 2 includes a middle region 21, two transition regions 22 located at both ends of the middle region 21, and two transition regions 22 respectively formed in the middle of the two transition regions 22. The fixed area 23 at one end of the area 21 is used for fixing with the metal frame 1 ; the two sides of the transition area 22 gradually narrow toward the middle area 21 .

Further, in order to prevent excessive concentration of stress at the connection between the intermediate region 21 and the transition region 22 and the connection between the transition region 22 and the fixed region 23, the connection between the intermediate region 21 and the transition region 22 and the connection between the transition region 22 and the fixed region 23 The joints of each include an arc-shaped transition portion 24.

More specifically, the two sides of the intermediate region 21 are arranged as straight sides parallel to each other, and the two sides of the transition region 22 are arranged as symmetrically arranged hypotenuses. Through the above arrangement, the strain can be more evenly concentrated in the middle region of the aluminum alloy sheet.

In the above embodiment, it is defined that the length direction of the metal frame 1 is the first direction, the width direction of the metal frame 1 is the second direction, and the height direction of the metal frame 1 is the third direction; The metal sheet 2 is arranged along the first direction; the size of the metal outer frame 1 in the first direction is 95mm, the size of the metal outer frame 1 in the second direction is 45mm, and the size of the metal outer frame 1 in the third direction is The size of the frame 1 is 5mm; the size of the middle zone 21 in the first direction is 20mm, the size of the middle zone 21 in the second direction is 15mm, and the size of the middle zone 21 in the third direction is 0.2mm; The size of the fixed area 23 in one direction is 7 mm, the size of the fixed area 23 in the second direction is 35 mm, and the size of the fixed area 23 in the third direction is 0.2 mm. The length is 77mm. In the design of the entire device, the shape and size of the metal sheet 2 are particularly critical. The sample 3 is pasted on the middle area 21 of the metal sheet 2. In order to prevent the strain from concentrating on the transition area 22, a long distance is required for a slow transition. Under the premise of the same size of the metal frame 1, the narrower the middle area of the metal sheet 2 carrying the sample 3, the greater the strain, but the quality of the sample 3 that can be pasted is limited. (It is difficult to obtain high test data quality when the middle area is too narrow and the quality of the sample is insufficient.) In the experiment, it is also necessary to take into account the inner diameter of the measuring instrument cavity and the demand for sample volume.

In a specific embodiment, the device further includes a connecting part 4 formed on the metal outer frame 1 for connecting with external equipment, and the connecting part 4 is used for connecting the device with a test instrument.

In a specific embodiment, the device includes two clamping fixtures 5 arranged at both ends of the metal sheet 2 and fixed to the metal frame 1, and the metal sheet 2 is located between the two clamping fixtures 5; A clamping fixture 5 is configured to clamp and fix the metal sheet 2 in the metal outer frame 1 .

Further, the metal frame 1 is made of Invar alloy; the clamping fixture 5 and the metal sheet 2 are both made of 6061 aluminum alloy; the clamping fixture 5 fixes the metal sheet with M3 stainless steel screws with a length of 4mm, and the clamping fixture Connect and fix the metal sheet 2 with the Invar alloy frame by M3 stainless steel screws with a length of 12mm (namely the top screw 6); the screws on the entire device can be tightened, which mainly plays the role of fixing the metal sheet 2 instead of stretching the metal The role of sheet 2.

In summary, the present invention can be widely applied to a variety of layered single crystal samples. This device can not only realize the detwinning of single crystal samples, but also transfer the remaining uniaxial strain to single crystal samples, so that the samples can be detwinned The basis of the crystal has a certain uniaxial strain.

In the experimental research, on the one hand, the improvement of the detwinning technology is beneficial to the study of the intrinsic properties of the sample and enhances the understanding of the research system; on the other hand, the introduction of uniaxial strain in the system may induce some novel physical phenomena Or cause changes in order parameters.

In another embodiment, the present invention also provides a method for detwinning of a layered single crystal sample, the method includes: fixing the two ends of the metal sheet 2 to the metal frame 1, and during the assembly process, the metal The two ends of the sheet 2 are fixed in the metal frame by the clamping fixture 5. Further, STYCAST 2850FT glue should be evenly applied on the contact position between the metal sheet 2 and the clamping fixture 5 and the metal frame 1, and heated at 65°C. Continue drying for 2 hours. The above operation can reduce the stress concentration around the screw hole corresponding to the M3 stainless steel screw, and prevent the metal sheet 2 from breaking or slipping along the screw hole direction during the stretching process, resulting in tension relaxation. and loss; the layered single crystal sample 3 is fixed on the metal sheet 2; in a low temperature environment, since the thermal expansion coefficient of the metal frame 1 is smaller than that of the metal sheet, the metal sheet 2 is subjected to tension and transmits the tensile strain to the sample 3 The sample 3 is analyzed; the analysis includes anisotropic resistivity test or elastic neutron diffraction measurement; the measurement is measured by the comprehensive physical property measurement system PPMS, and the analysis is performed by using matlab for data processing.

Taking FeSe, a layered single crystal with a small size in an iron-based superconductor, as an example (typical size 2*2*0.05mm ³ ), we characterized the detwinning effect of the device through a variety of experimental methods: (1) Combining comprehensive The physical property measurement system PPMS carries out transport measurement (detwinning FeSe single crystal anisotropic resistivity test); (2) elastic neutron diffraction measurement; the results are as follows:

(1) Transport measurement

The anisotropic resistivity measurement of detwinned FeSe single crystal is based on the comprehensive physical property measurement system (PPMS) combined with the multifunctional rod. Limited by the inner diameter of the PPMS cavity, the overall size of the device for detwinning of layered single crystal samples can be appropriately reduced to fit the PPMS cavity. It can be understood that the above operations are only for the corresponding reduction of the overall size. The principle does not change.

A FeSe single crystal sample was pasted on the center of the aluminum alloy sheet with Cytop, a hydrogen-free glue, and the (110) _T direction of the tetragonal phase of the single crystal sample was adjusted to be parallel to the straight edge of the aluminum alloy sheet. The intrinsic resistivity ρ _a and ρ _b of the detwinned FeSe single crystal in the a and b directions were measured by the Montgomery resistance measurement method; the resistance is characterized by (ρ _b -ρ _a )/(ρ _b +ρ _a ) The anisotropy can reach 6%, as shown in Figure 6, indicating that the FeSe single crystal is highly detwinned.

In order to further eliminate the influence of Poisson's ratio and characterize the uniaxial strain on the aluminum alloy sheet at low temperature, a strain gauge (model: WK-05- 062TT-350) measured the strain in the central rectangular area of the aluminum alloy sheet, and the results are shown in b in Figure 6 (in the detwinning experimental research, the default pressure direction is the b direction, which is the second direction, and the device is along the The pulling force is applied in the vertical direction, so the vertical direction is the direction a (that is, the first direction).

The two curves at b in Figure 6 correspond to the difference in strain in the first direction and the second direction in the uniform narrow rectangular area in the center of the aluminum alloy sheet when the screw 6 on the top of the device is tightened and loosened, respectively. For the former, the uniaxial strain in the uniform rectangular region can reach ε _vertical -ε _horizontal (ε _a -ε _b )=5×10 ^-3 at low temperature, which is enough to detwin FeSe; for the latter, only a very small residual strain.

Based on the above analysis, we can design the aluminum alloy sheet to be wide at both ends and narrow in the middle, so as to keep its elastic coefficient lower than that of other parts, so as to produce elastic deformation. The transport measurements have confirmed the practicability and scientificity of the device from various perspectives, and can successfully realize the detwinning of layered FeSe single crystals and the uniaxial strain of 5×10 ^-3 in the narrow central region of the aluminum alloy sheet at low temperature.

(2) Elastic neutron diffraction measurement

Elastic neutron diffraction is a well-established experimental probe for characterizing the detwinning ratio of devices. Elastic neutron diffraction can measure the Bragg diffraction of single crystal structure peaks. In neutron scattering or neutron diffraction experiments, cadmium (neutron absorption cross-section is large) can be used to wrap the Invar alloy of the device outer frame, and redundant aluminum alloy sheets, etc., and only part of the sample is exposed to the neutron beam. range to help reduce background signal.

Referring to Fig. 7, there are multiple FeSe single crystals adhered on the aluminum alloy sheet, and the (110) _T direction of the tetragonal phase is parallel to the a/b direction. The detwinning effect of the device was characterized by the "Xingzhi" cold triaxial polarization spectrometer located on the neutron source of the China Advanced Research Reactor (CARR Reactor) of the China Institute of Atomic Energy.

a and b in Figure 8 are the neutron diffraction results of the structural peaks (020) of the detwinned FeSe (tighten the top screw 6) and the twinned FeSe (loosen the top screw 6), respectively, and the corresponding temperatures of the two curves They are 20K (T< _TS ) and 120K (T> _TS ) respectively.

For twinned FeSe single crystals, the intensity of the diffraction peak at (020) weakens and the half-maximum width widens below the structural phase transition temperature. After Gaussian function fitting, it was found that the diffraction peak at (020) split from one peak to two peaks with similar spectral weights as the temperature decreased. The appearance of these two peaks is because after entering the twin crystal state, the structural peak (020) o has both the contribution of the (020) _o peak and the contribution of the (200) _o peak, and the contributions of the two are equal. Overall, above and below T _S , the spectral weight of the diffraction pattern is basically conserved, as shown in b in Figure 8.

For the detwinned FeSe single crystal, the Gaussian function is used to fit the diffraction spectra at the structural peaks (020) of T< _TS and T> _TS , and it is found that when T< _TS , the peak splitting also occurs , the corresponding two peaks have contributions from both the (020) _o peak (right side) and the (200) _o peak (left side), but the spectral weights of the two peaks are significantly different. Using (I(020) _o -I(200) _o )/(I(020) _o +I(200) _o ) to calibrate the detwinning ratio can reach about 71%. Among them, I(020) _o and I( 200) _o represents the intensity of the structural peaks (020) _o and (200) _o in the orthorhombic phase. And T<T _S and T>T _S , both spectral weights are conserved, as shown in a in Figure 8 .

Based on the above analysis, the device can directly partially detwin a large number of FeSe single crystals at the same time (the detwin ratio is as high as ~71%), and the whole device effectively reduces the influence of background signals. The wide application of this device will help researchers to study the intrinsic properties of similar systems.

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those of ordinary skill in the art can also make It is impossible to exhaustively list all the implementation modes here, and any obvious changes or changes derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims (8)

1. An apparatus for de-twinning a layered single crystal sample, comprising:

a metal outer frame with an inner cavity; and

the metal sheet is positioned in the inner cavity of the metal outer frame;

two ends of the metal sheet are fixed with the metal outer frame;

the thermal expansion coefficient of the metal outer frame is smaller than that of the metal sheet;

the metal sheet is configured to bear and fix a sample, and under a low-temperature environment, due to the difference of the thermal expansion coefficients of the metal outer frame and the metal sheet, the metal sheet is subjected to tension and transmits tensile strain to the sample;

the metal sheet comprises a middle area, two transition areas positioned at two ends of the middle area, and two fixing areas which are respectively formed at one end of the two transition areas far away from the middle area and are used for being combined and fixed with the metal outer frame;

the two side parts of the transition area gradually narrow towards the middle area;

defining, wherein the length direction of the metal outer frame is a first direction, the width direction of the metal outer frame is a second direction, and the height direction of the metal outer frame is a third direction;

the metal sheet is arranged along the first direction;

the size of the metal outer frame in the first direction is 95mm, the size of the metal outer frame in the second direction is 45mm, and the size of the metal outer frame in the third direction is 5mm;

the size of the middle area in the first direction is 20mm, the size of the middle area in the second direction is 15mm, and the size of the middle area in the third direction is 0.2mm;

the size of the fixed area in the first direction is 7mm, the size of the fixed area in the second direction is 35mm, and the size of the fixed area in the third direction is 0.2mm.

2. The apparatus according to claim 1, wherein the junction of the intermediate region and the transition region and the junction of the transition region and the fixing region each comprise an arc-shaped transition portion.

3. The device for the layered single crystal sample twinning regression according to claim 1, wherein both side portions of said middle region are straight-sided;

the two side parts of the transition area are inclined edges which gradually gather together.

4. The apparatus as claimed in claim 1, further comprising a connecting part formed on the metal frame for connecting to an external device.

5. The device for the de-twinning of the layered single crystal sample according to claim 1, wherein the metal outer frame is made of invar alloy; the metal sheet is made of 6061 aluminum alloy.

6. The device for the layered single crystal sample twinning regression as claimed in claim 1, wherein said device comprises two holding fixtures arranged at two ends of the metal sheet and fixed with the metal outer frame, said metal sheet is located between the two holding fixtures; the two clamping fixtures are configured to clamp and fix the metal sheet within the metal frame.

7. A method for de-twinning a layered single crystal sample using the apparatus of any one of claims 1-6, the method comprising:

fixing two ends of the metal sheet with the metal outer frame;

fixing the layered single crystal sample on a metal sheet;

under a low-temperature environment, because the thermal expansion coefficient of the metal outer frame is smaller than that of the metal sheet, the metal sheet is subjected to tension and transmits tensile strain to a sample;

analyzing the sample;

the analysis includes anisotropic resistivity testing or elastic neutron diffraction measurements.

8. The method for de-twining a layered single crystal sample according to claim 7,

the two ends of the metal sheet are fixed in the metal outer frame through the clamping fixing piece, and the method further comprises the following steps:

uniformly coating STYCAST 2850FT glue on the contact position of the metal sheet, the clamping and fixing piece and the metal outer frame, and baking for 2 hours at the temperature of 65 ℃.

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