Measurement of High-Temperature to
Superconductor Used Magnetic Feeler
Dr.bahaa H. Rabee Dr.khalid Al-Amar
Babylon University, College of Education, Department of Physics
E-mail:dr_bahaa19@yahoo.com
Key word: measurement, superconductor, feeler
Abstract
The high-temperature superconductor (HTS)will generally break the superconducting state of current density Jms ,greater than the critical current density Jc , when the resistance Rms of the film pelt to the flow of current occurs in the absence of an excitation magnetic field. The magnetic sensitivity S of the sensor when exposed to an excitation magnetic field. Was found to be about 150?(10-3 T) for Bi-Pb-Sn-Ca-Cu-O(BPSCCO)magnetic sensor, and about 12?(10-2T)for Y-Ba-Cu-O (YBCO)magnetic sensor. Therefor, the magnetic sensitivity of(BPSCCO)magnetic sensor is about 150 times greater than of a giant magnetoresistancs (GMR)sensor.
ملخص
أن الدرجات الحرارية العالية للموصلات الفائقة (HTS) تتولد من تشقق تدفق التيار عند أعلى كثافة له Jms , والتي تكون أعلى من كثافة التيار الحرج Jc , حيث تتشكل المقاومة Rms ,عند تدفق التيار ولا تظهر عند اختفاء المجال المغناطيسي ,كذالك يظهر التحسس المغناطيسي S عند المجس باختفاء المجال المغناطيسي الخارجي , ويكون موجود بحدود 150? ( -3T10) من المركب Bi-Pb-Sn-Ca-Cu-O (BPSCCO)كمجس مغناطيسي . وبحدود 12? (10-2T) للمركب YBaCuO (YBCO) كمجس مغناطيسي . ولذالك فأن الحساسية المغناطيسية للمجس (BPSCCO) تكون بحدود 150 مرة أكبر من أعظم مجس للمقاومة المغناطيسية (GMR).
Introduction
It has been determined that it is necessary to develop a highly sensitive magnetic sensor [1] . the resistance Rms to the flow of current of a thick high-critical temperature superconducting (HTS) film occurs at value of current density Jms greaAer than that of cribcal current density Jc under magnetic held of OT [2] . The magnetic sensitivity S at such HTS sensors when exposed to an excitation magnetic field , were found to be about 200% \(10?3 T) for a B:-Pb-Sr-Ca-Cu-O (BPSCCO) magnetic sensor and about 71.(10?3T) for a Y Ba-Cu-O (YBCO) magnetic sensor That is, the magnetics sensitivity of the BPSCCO magnetic sensor was about 200% \(10?3T) about 200 times greater than that of a giant magneto resistance (GMR) sensor[3]. The YBCO magnetic sensor [5] retained a residual resistance after 3 thermal cycles between temperatures of 77.4 K and 300 K,
II. EXPERIMENTAL PROCEDURE
A. Fabrication of the Thick HTS Film
Prior to the process of spraying, a MgO(100) single-crystal substrate (20 mm in length, 10 mm in width, and 0.5 mm thick) was masked, using masking tape, in order to fabricate the magnetic sensor with a given geometry. The paste used in the spraying process was consisted of a commercial HTS powder milled into a fine powder by use of a planetary type agate grinder. (the dominant particle size of the BPSCCO and YBCO powder was about 3 ), and ethylene glycol HOCH CH OH . The paste was then prepared by homogeneously mixing at a weight ratio of the powder to ethylene glycol of 1/3. The paste was sprayed on the MgO(100) substrate with the use of an airbrush. The specimens were then dried on a hot plate at 230 for 10 minutes. This process was repeated about 250 times. The masking tape was then removed after the completion of the spraying and drying processes. The specimens then underwent two processes, namely, the quenching and sintering processes for thick BPSCCO and YBCO films. The quenching process of the thick HTS films was performed to improve the superconducting characteristics [7].
B. Quenching and Sintering Processes
The thick BPSCCO films, as shown in Fig. 1 were heated in a flow of dry air to 845 [8] at the rate of , through the use of a programmable electric furnace, and cooled to room temperature at the same rate. Two plateaus in the BPSCCO quenching process were maintained at 200 for 1 hour,
Fig. 1. Temporal distribution of temperature during the quenching and sintering processes of the thick BPSCCO film magnetic sensor. The solid and dashed lines represent the temperature (left axis) and flow rate of dry air (right axis), respectively, for the quenching process (QP), and the sintering process (SP).
Fig. 2. Temporal distribution of temperature during the quenching and sintering processes of the thick YBCO film magnetic sensor. The solid and dashed lines represent the temperature (left axis) and flow rate of dry air (right axis), respectively, for the quenching process (QP), and the sintering process (SP).
and then 845 for 5 hours. Two plateaus were maintained in the sintering process, namely, at 845 for 20 hours, and then 825 for 30 hours. On the other hand, the thick YBCO films were sintered at a rate of , making use of a programmable electric furnace in the heating and cooling processes. Two plateaus as shown in Fig. 2, in the quenching process were maintained at 200 for 1 hour, and 933 for 30 minutes. Three plateaus were maintained in the YBCO sintering process, 200 for one hour, 933 for 30 minutes, and 570 for 1 hour during the drying of the thick film, the melting process, and during the growth of crystallized (perovskite structure) grain in the film, respectively.
C. Holder for Thick HTS Film
The thick BPSCCO and YBCO film magnetic sensors and Pt thermometer were fixed with grease (Apiezon N) to a holder composed of oxygen free copper (OFC) with a copper spiral (diameter of about 2.0 mm) for simplifying the temperature control. The sensors were wrapped with several turns of fluoroplastic (PTFE) tape in order to avoid sudden temperature changes.
Fig. 3. Schematic illustration of the holder used in the measurements. Here, (a), (b), (c), and (d) are the Pt thermometer, copper holder, thick HTS film, and the copper spiral, respectively.
Fig. 4. Typical plots of temperature T dependence on the resistance R for Sensors #1 (BPSCCO, solid squares) and #2 (YBCO, open circles) in the absence of an excitation magnetic field. Here, the values of R were normalized by the resistance R (T = 150K) at 150 K.
III. RESULTS AND DISCUSSION
The size and characteristics of typical thick HTS film magnetic sensors are listed in Table I. Fig. 4 shows the typical dependence of the resistance on the temperature for Sensors #1 (BPSCCO, solid squares) and #2 (YBCO, open circles) in the absence of an excitation magnetic field . The values of in the figure have been normalized by the resistance at 150 K. The values of for Sensors #1 and #2 were determined as 84 K and 85 K, respectively.
Fig. 5 shows the typical dependence of the resistivity on the current ensity for Sensors #1 (BPSCCO, open and solid squares) and #2 (YBCO, open and solid circles) in the absence of a magnetic field , under temperature conditions of 77.4 K. In this figure, the open and solid squares display the characteristics for Sensor #1, after the first and 300th
thermal cycles between temperature of 77.4 K and 300 K, respectively.
Fig. 5. Characteristics of the resistivities _ for Sensors #1 (open and solid squares) and #2 (open and solid circles) as functions of the current density applied to the sensor in the absence of a magnetic field (B = 0 T), under temperature conditions of 77.4 K. Here, the open and solid squares are the characteristics for Sensor #1 after the first and 300th thermal cycles between temperature of 77.4 K and 300 K, respectively. The open and solid circles are the characteristics for Sensor #2 after the first and 3rd thermal cycles, respectively.
Fig. 6. Magnetic sensitivity S for Sensors #1 (solid squares) and #2 (open
circles) as a function of the resistivity _ of each sensor under temperature
conditions of 77.4 K. Here, S is defined as in (1).
The open and solid circles reveal the characteristics for Sensor #2 after the first and 3rd thermal cycles, respectively. From the present results, it is found that the BPSCCO magnetic sensors maintain excellent durability for practical use. That is, after being exposed to 300 thermal cycles, the characteristics of the BPSCCO magnetic sensor were found to exhibit no remarkable changes. In the case of the YBCO magnetic sensor, however, the sensor retained a residual resistance after 3 thermal cycles between temperatures of 77.4 K and 300 K, under temperature conditions of 77.4 K. In the present research, is defined as the value of current density greater than that of the critical current density when resistance to current flow occurs on the sensor at 77.4 K. In addition, it is found that the values of resistivity for sensors increase as the values of increase. That is, the value of can be readily controlled by the value of . Fig. 6 displays the magnetic sensitivities for Sensors #1 and #2, as functions of the resistivity of the sensors, in the
Fig. 7. Typical plots of the dependence of the resistance R (B ) on the excitation magnetic field B for Sensor #2 for applied value of J of 865 A=m under temperature conditions of 77.4 K. Here, the values of R were normalized by the resistance R (B = 0 T). The open and solid circles are the characteristics after the first and 3rd thermal cycles, respectively
.
Fig. 8. Typical plots of the dependence of the resistance R (B ) on the excitation magnetic field B for Sensor #1 for applied value of J of 100 A=m at 77.4 K. Here, the values of R were normalized by the resistance R (B = 0T). The open and solid squares are the characteristics after the first and 300th thermal cycles, respectively.
magnetic range of 0 T to . Here, the magnetic sensitivity is defined by
(1)
It is found that the values of increase as the values of decrease. Namely, the value of can be readily controlled by the value of . Figs. 7 and 8 show the typical plots of the dependence of the resistance for Sensors #2 (YBCO, open and solid circles), and #1 (BPSCCO, open and solid squares) on the excitation magnetic field between values of 0 T to , respectively. In this figure, the values of were normalized by . These magnetic characteristics for Sensors #1 and #2 are for applied values of of 100 and 865 , respectively, when the value of current density is greater than that of the critical current density . The open circles and open squares in Figs. 7 and 8, respectively, represent the characteristics under first cooling (77.4 K). In addi1692
Fig. 9. Dependence of the resistance R (B ) of Sensor #1 on the excitation magnetic field B for an applied values of J of 100 A=m under temperature conditions of 77.4 K. The values of R were normalized by the resistance R (B = 0T).
tion, the solid circles in Fig. 7 and solid squares in Fig. 8 represent the characteristics for 3rd and 300th thermal cycles, respectively. The agnetic sensitivity of Sensor #2 was destroyed by repeated thermal cycles. However, for the Sensor #1, the BPSCCO magnetic sensor, it was found that the dependence of on the exhibited no significant changes after
being exposed to 300 thermal cycles. The value of for Sensor #1 at was about , being about 200 times greater than that of a GMR sensor. In addition, the ratio is about 1.7 times that of a MI sensor. As another example, hysteresis characteristics were observed for Sensor #1, when it was exposed to a greater range of , such as shown in Fig. 9. The value of
for a of , however, exhibited an increase of about 100 times that of the resistance found for a of 0 T. This is an amazing display of sensitivity. The present authors are now investigating the electrical application of the resistance change, and the relationship between the present magnetic characteristics and the particle size distribution of the HTS powder.
IV. CONCLUSIONS AND SUMMARY
The present authors have succeeded in constructing a magnetic sensor using a thick superconducting BPSCCO film. The characteristics of the sensor can be summarized in the following:
1) The magnetic sensitivity between 0 T to , was about for the BPSCCO magnetic sensor. Namely, it is about 200 times greater than that of a GMR sensor, such as shown in the results in Fig. 8.
2) Hysteresis characteristics in the results for the BPSCCO magnetic sensor were not observed over the range of the excitation magnetic field , from 0 T to . In addition, the characteristics exhibited symmetry with respect to during the application and withdrawal of , such as shown in the results in Fig. 8.
3) After testing through more than 300 thermal cycles between temperatures of 77.4 K and 300 K, the characteristics of the BPSCCO magnetic sensor were found to exhibit no significant changes in magnetic responses, such as shown in Figs. 8 and 9. Namely, these results were found to be important criteria, fundamental in the design of highly sensitive, more reliable thick HTS film magnetic sensors, for practical use.
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