Single Domain GdBCO Bulk Superconductors Research Articles

The levitation force and stiffness enhancement of single domain GdBCO bulk superconductor by an axial background magnetic field

How to improve the levitation force (FL) and its stiffness between a permanent magnet and a REBCO bulk superconductor is one of the most key and attractive problems to be solved for practical applications. In this paper, we provided a novel hybrid magnet added superconductor system (HMS) to enhance the levitation force and the stiffness, the HMS sample is assembled by a single domain GdBCO bulk with an attached permanent magnet (PM) serving as an axial background magnetic field. The results indicate that (1) the FL increased first and decreased then with the increase of the PM diameter (dPM), the largest FL is achieved when the dPM approaches the diameter of the GdBCO bulk, FL has been improved up to 152% with a thinner PM; (2) the FL increased with the increase of the PM thickness and saturated at a certain value, FL have been improved up to 168% with a thicker PM; (3) the stiffness of FL has been improved up to 187% and 201% with the increase of the PM diameter and thickness; (4) the FL and its stiffness enhancement dependent on the positive trapped field of the field cooled HMS samples. The results are of great significance to improve the performance and stability of maglev systems, the mechanism for enhancing the levitation force and stiffness property has been investigated in details.

A Practical Processing Method for the Fabrication of NdBCO Seed Crystals and High-Performance Single-Domain GdBCO Bulk Superconductors

NdBCO seed crystals and high-performance GdBCO bulk superconductors were prepared successfully by a modified top-seeded melt-textured growth (TSMG) process and by Gd + 011 top-seeded infiltration growth (TSIG) process. The modified TSMG process used a new composition powder (NCP, 0.9 Nd2O3 + 2.4 BaCuO2 + CuO) instead of the conventional composition powder (CCP, NdBa2Cu3O7-x + 0.4 Nd2BaCuO5), the GdBCO bulk superconductor seeded by the self-made NdBCO seed crystal. In the whole procedure above, only one precursor powder (BaCuO2) needs to be sintered, three kinds of powder and three pellets are required, so time and energy consumption were greatly reduced. The results of thermal analysis and X-ray diffraction (XRD) patterns revealed the reaction mechanism of the modified TSMG process. Superconductivity properties of the GdBCO sample were measured employing a levitation force measurement system and a vibrating-sample magnetometer (VSM); the maximum value of the levitation force of the GdBCO sample was 44.78 N (77 k, 0.5 T); the onset superconductivity transition temperature (Tc) was approximately 93.7 K; the transition width was 6.2 K, and the maximum value of critical current density (Jc) was 1.5 × 105 A∙cm−2 (0 T, 77 K). These results indicate that, by combing the modified TSMG process and Gd + 011 TSIG process, a practical processing method for preparing the NdBCO seed crystals and the high-performance single-domain GdBCO bulk superconductors was developed.

The effect of the magnetic field distribution of permanent magnets on the trapped field properties of a single domain GdBCO bulk superconductor

The trapped field properties of a single domain GdBCO bulk superconductor with a diameter of 32 mm after being magnetized with different permanent magnets under a field cooling state at 77 K have been investigated. The results show that the maximum trapped field of the sample (Bmtr) is nearly saturated when the diameter of the permanent magnet d ≥ 20 mm, but the trapped magnetic flux of the sample (Φs) is nearly saturated when d ≥ 30 mm. This indicates that the largest trapped magnetic flux can be obtained when the size of the permanent magnet is close to that of the sample, and it is not necessary to use a more permanent magnet. In addition, a new and unusual phenomenon is found in that Φs is greater than the magnetic flux of the permanent magnet (ΦPM) when the diameter ratio between the permanent magnet and the sample is less than a certain value, such as 0.63 in this experiment. The relationship between Φs and ΦPM was well expressed as These results can provide a new method to design and control the trapped field properties of a single domain REBCO bulk superconductor during practical applications.

How to Control the Gd211 Particles and Enhance the Levitation Force of Single Domain GdBCO Bulks Prepared by the Gd+011 TSIG Method

In order to control and refine Gd211 particle size in GdBCO bulks, two group of single domain GdBCO bulk superconductors have been prepared with different solid phase pellets sintered at different temperature (T) and times by the Gd+011 TSIG method. The results of the first group of single domain GdBCO bulks indicate that: the average size of Gd211 particles in precursor solid phase pellets increase with T increasing up to 1200 °C; the density of the precursor solid phase pellets increases with the increasing of T when T is larger than 950 °C, but lower than that of the as-pressed pellets when T less than 1000 °C; the average size of Gd211 particles in the single domain GdBCO bulks decreases first and increases then with the increasing T; the maximum levitation force is obtained in the sample with a relatively larger size of Gd211 particles and higher density. The second group of samples has also been prepared with the solid phase pellets sintered at 1000 °C but with different times, the results indicate that: the largest levitation force is about 38% higher than that of the best samples mentioned above. The results are discussed in detail.

The Effect of Cone Additional Permanent Magnet Thickness on Magnetic Field Distribution and the Levitation Force of Single Domain GdBCO Bulk Superconductor

It has been investigated that the interaction force between truncated cone permanent magnet (PM) and a GdBCO bulk (HTSC) superconducting permanent magnet (SCPM) magnetized by a truncated cone permanent magnet in their configurations at 77K. The influence of two configurations in different thickness of truncated cone permanent magnets of single domain GdBCO bulk capture field and superconducting magnetic levitation force results. The maximum superconducting magnetic levitation force first increases as H increase, and then decreases with H when it reaches a certain value, from 5.7N to 16.6N at first, and then it decreases to 3.8N. The vertical component of the magnetic field intensity on the top surface (h=2mm) of truncated cone permanent magnet first increases, and then decreases also, from 0.20T to 0.54T, and then decrease to 0.25T. These results indicate that the levitation force of high temperature superconductor bulk can be effectively improved by scientific choosing of shape and size of permanent magnet, and reasonable designing of the system configurations, which is very important during the practical design and applications of superconducting magnetic levitation system.

A Low-Cost Fabrication Technique for the Growth of Single-Domain GdBCO Bulk Superconductor from Raw Metal Oxides

A single-domain GdBCO bulk superconductor is usually fabricated using a mixture of pre-reacted precursor powders (including GdBa2Cu3O7−δ and Gd2BaCuO5) by the top-seeded melt texture growth (TSMTG) process. However, the synthesis of pure-phase precursor powder by the solid-state sintering reaction can not only consume time for weeks but also prolong the fabrication process and can lead to a low-efficiency and high-cost process. In this paper, we reported the successful growth of single-domain GdBCO bulk superconductors by the top-seeded metallic oxide melt growth (TS-MOMG) process in which the raw materials of Gd2O3, BaO, and CuO, the three different metallic oxides, are just involved to fabricate the single-domain GdBCO bulk superconductors. After detailed investigations in the morphology, levitation force, trapped magnetic field, and critical temperature of the grown samples with different ratios, it was found that the simplified precursor-phase source can be used to fabricate the single-domain GdBCO bulk superconductors more efficiently, which can combine the crystal growth procedure and greatly economize the preparation cost and the time to the most extent.

Effect of inner diameter of hollow cylindrical permanent magnet on levitation force of single domain GdBCO bulk superconductor

The influence of inner diameter of hollow cylindrical permanent magnet on the levitation force of single domain GdBCO bulk superconductor is investigated by measuring the levitation force between the hollow cylindrical permanent magnet and the single domain GdBCO bulk superconductor. The results show that the levitation force is closely related to the inner diameter of the hollow cylindrical permanent magnet when the inner diameter (d) increases from 0 mm to 26 mm (minimum measuring gap distance Z=2 mm), and all the superconducting magnetic levitation force curve shows magnetic hysteresis phenomenon. With the increase of the inner diameter of the hollow cylindrical permanent magnet, the levitation force at a minimum distance decreases gradually from 14.8 N at d=0 mm to -0.1 N at d=26 mm. The levitation force at the minimum gap distance is negative when d ≥ 20 mm. When 0 mm ≤ dd ≥ 5 mm. The larger magnetic field strength of the superconductor can be obtained, and the levitation force can be effectively improved by the scientific and reasonable designing of the permanent magnet structure. The results have certain guiding significance for designing and optimizing the magnetic suspension bearing system, ring track and superconductor.

Influences of BaO doping on the properties of single domain GdBCO bulk superconductors (II)

In order to inhibit the Gd/Ba substitution in the growth process effectively, a series of single domain GdBCO bulk superconductors with different ratios of BaO additions in the solid phase pellet is successfully fabricated by the modified top seeded infiltration growth technique on the basis of previous research. In the present work, the macroscopic feature, microstructure and critical current density (Jc) of the single domain GdBCO bulk superconductor are investigated in detail. From the top view of the surface of the single domain GdBCO bulk superconductor, all of the samples exhibit clearly the fourfold growth sector boundaries on their top surfaces, and spontaneous satellite grains are observed in none of these samples. It can be seen that the different ratio of BaO addition (from 1 wt% to 4 wt%) cannot affect the growth morphology of the single domain GdBCO bulk superconductor. At the same time, for observations of the microstructure, the small test specimens of dimensions about 2 mm2 mm2 mm are cut from the top surface of the singe domain GdBCO bulk superconductors with different BaO doping ratios and at a distance 5 mm away from the seed, then microstructure analysis is performed in the cleavage phane of the test specimen by using scanning electron microscope. For the sample with 1 wt% BaO doping, the derivative phase of GdBCO (Gd123ss) is found in the Gd123 superconducting matrix. To detect the atomic ratio of the Gd123ss, energy dispersive X-ray spectrometry measurement is carried out on the samples. It is shown that the atomic ratio of the Gd123ss phase is Gd:Ba:Cu=1.566:1.459:3, which proves successfully that the Gd123ss is a kind of phase with lack of barium. With the increase of BaO doping, the phenomenon of lack of barium is effectively controlled and, the nano Gd123ss phase is generated as the flux pinning centre which can be used to improve the superconducting properties in the growth process of GdBCO bulk superconductor. This results can be concluded that the proper doping ratio can control the element substitution effectively, and the solid solution phase can be greatly reduced to some extent, and the critical current can be improved to a certain extent when the amount of BaO added ranges from 2 wt% to 4 wt%, which is very helpful in inhibiting the Gd/Ba substitution and fabricating the high-quality single domain GdBCO bulk superconductors.

Effect of Li doping on the superconducting properties of single domain GdBCO bulks fabricated by the top-seeded infiltration and growth process

Single domain GdBCO bulk superconductors have been fabricated by the top-seeded infiltration and growth process (Gd+011 TSIG) with solid phase compositions of (1-x)(Gd2O3+1.2BaCuO2)+xLi2CO3, (x=0, 0.04, 0.08, 0.10, 0.12, 0.16wt%). The effect of Li2CO3 doping on the growth morphology, microstructure, levitation force, trapped field and critical temperature (Tc) of single domain GdBCO bulks have also been investigated based on these samples. The results show that the single-domain GdBCO bulks can be fabricated when x is in the range of 0–0.16wt%. The size and distribution of Gd211 particles are not influenced by the Li2CO3 doping in the samples. The Tc of the samples decrease from 92.5K (x=0wt%) to 89.5K (x=0.16wt%) when x increases. The decreasing trend of Tc was caused by the substitution of Li+ on Cu2+ site in the GdBCO crystal. Both of the levitation forces and trapped fields of the samples increase first and then decrease with the increase of x; both of the largest levitation force of 38.5N（77K，0.5T） and the largest trapped field of 0.31T（77K，0.5T） are obtained in the sample when x=0.10wt%. These results show that appropriate Li doping is an effective way to enhance the flux pinning force and the other physical properties of GdBCO bulk superconductors fabricated by the Gd+011 TSIG method.

Influences of BaO doping on the properties of singe domain GdBCO bulk superconductors

In this work, a series of single domain GdBCO bulk superconductors with different ratios of BaO addition in the solid phase pellet, is successfully fabricated to inhibit the Gd/Ba substitution in the growth process by the modified top seeded infiltration growth (M-TSIG) technique. The reaction of the precursor powders, the growth morphology, the magnetic levitation force (F), the trapped magnetic flux (Btr) and critical temperature (Tc) of the single domain GdBCO bulk superconductors are investigated in detail. First, the differential thermal analysis is performed on the precursor powders of 10 mg solid phase pellet (containing various amounts of BaO) and 15 mg liquid phase pellet in order to investigate the melting temperature (Tm) and the peritectic temperature (Tp) of the GdBCO superconductor system. The results show that the melting point of the precursor powder decreases by nearly 8℃ as the BaO composition increases from 0 wt% to 4 wt%, which leads to Tp decreasing with BaO content increasing. Second, the top view morphologies of the GdBCO samples are also discussed. All of the samples exhibit clear, fourfold growth sector boundaries on their top surfaces, and spontaneous satellite grains are observed in none of these samples. It can be seen that the different ratio of BaO addition cannot affect the growth morphology of the single domain GdBCO bulk superconductor. And thirdly, the levitation force and trapped field of each of the samples are measured under a zero field cooling state at 77 K by the three-dimensional magnetic force and field device. The values of the levitation force for the samples are slightly different for different ratios of BaO additions. The largest levitation force is 35 N, which is obtained in the sample with 2.5 wt%, and the smallest one is 28 N in the sample with 1 wt% BaO addition. And also, the trapped field of the sample can be attributed simply to the variation in the pinning strength. It can be obviously seen that these values fluctuate between 0.28 T and 0.32 T for these samples. Finally, the critical temperatures of the samples are measured by the vibrating sample magnetometer with an external magnetic field of 0.01 T. The samples exhibit outstanding features of high Tc, which indicates that these samples are of good quality and the Gd/Ba substitution is inhibited by the BaO addition. The above results show that the values of melting temperature (Tm) and peritectic temperature (Tp) of the samples have the decrease tendencies, and the superconducting properties of the samples (such as F, Btr and Tc) can be improved to a certain extent when the amount of BaO added ranges from 2 wt% to 4 wt%, which are very helpful in inhibiting the Gd/Ba substitution and fabricating the high-quality single domain GdBCO bulk superconductors.

Comparison of the superconducting properties in GdBCO bulk superconductors fabricated with two different solid phases

In this paper, we investigated the two fabrication processes of single-domain GdBCO bulk superconductors with new solid phase sources (NSPs) and conventional solid phase sources (CSPs) by the modified top-seeded infiltration and growth (TSIG) technique. The CSPs is Gd2BaCuO5 powder, and the NSPs is made of a mixture of powders of Gd2O3 and BaCuO2. The reaction of the solid phase, morphology, microstructure and superconducting properties of the GdBCO samples were investigated. The properties of the sample with the NSPs have been improved compared with those of the sample fabricated by the CSPs. It is found that the improvement method cannot only increase the stability of the sample to complete the growth of the whole bulk during the TSIG process at a high temperature but also economize the raw material and experimental time. The results are helpful to us for the fabrication of large-grain single-domain GdBCO bulk superconductors using the improvement process method.

Effect of Ni2O3 doping on the properties of single domain GdBCO bulk superconductors fabricated by a new modified top-seeding infiltration and growth process

Single-domain GdBCO bulk superconductor (20 mm in diameter) has been fabricated by a top-seeding infiltration and growth (TSIG) mathod, it has a new solid phase of [(1-x)(Gd2O3+1.2BaCuO2) + x Ni2O3] (where x =0, 0.02, 0.06, 0.10, 0.14, 0.18, 0.30, 0.50 wt%). Effect of Ni2O3 additions on the growth morphology, microstructure, critical temperature Tc, magnetic levitation force, and trapped flux of single-domain GdBCO bulks have been investigated. Results show that the single-domain GdBCO bulk can be gained when x is in the range of 0-0.50 wt%; and the Gd211 particles are not affected by the Ni2O3 doping in the samples. The Tc of the samples decrease from 92.5 K (x=0 wt%) to 86.5 K (x=0.50 wt%) when x increases from 0 to 0.50 wt%, which is caused by the substitution of Ni3+ for Cu2 +. Both of the levitation force and trapped field of the samples increase first and then decrease with the increase of x; the largest levitation force of 34.2 N is obtained for the samples with x=0.14 wt%, and the largest trapped field of 0.354 T is obtained for the samples with x=0.10 wt%. The change of the levitation force and trapped field of the samples is closely related to the doping content x. As is known, the doping of Ni2O3 can result in substitution of Ni3+ for Cu2+ at its site in GdBCO crystals, which can reduce the critical temperature Tc of the samples; although Tc and the physical properties of the samples is reduced with the increase in the doping amount of Ni2O3, but at the same time, the substitutions of Ni3 + for Cu2 + in GdBCO crystals can produce local lattice distortions, which can act as magnetic flux pinning centers to improve the properties of the samples. The highest Tc is obtained in the samples without any Ni2O3 additions (x=0), but the magnetic flux pinning force of the samples is weak, so both of the levitation force and trapped field of the samples are relatively lower. When the doping content x ≤ 0.14 wt%, although the Tc is reduced slightly, it still has a value higher than 90 K; and the magnetic flux pinning force in the samples, due to the substitutions of Ni3+ for Cu2 +, would increase with the increase of doping content x, and result in an enhancement of levitation force and trapped field. When the doping content x is greater than 0.14 wt%, the magnetic flux pinning force of the samples is still increasing with the increase of x, but the Tc of the sample is significantly reduced and even less than 90 K, and finally result in an decrease of levitation force and trapped field. Only when the doping amount of Ni2O3 is appropriate, both of Tc and magnetic flux pinning force are of a relative optimal value, and lead to an enhancement of levitation force and trapped field.

采用顶部籽晶熔融辅助熔渗法制备高性能单畴GdBCO超导块材

In this paper, high performance and large single domain GdBCO bulk superconductors have been successfully fabricated by the top-seeded-melt-texture-infiltration-growth process (TSMT-IG). The effect of the growth morphology, growth interface, the magnetic levitation force and trapped flux of single domain GdBCO bulk superconductors has been investigated. The above result indicates that, the utilization of NdBCO seed crystal and the production efficiency of the single domain GdBCO bulk superconductor can be effectively improved by the new TSMT-IG process, which can inhibit the random nucleation phenomenon at some extent during the process of crystal growth. In addition, the application of new technology also helps to improve the growth performance of GdBCO samples.

Fabrication of single domain GdBCO bulk superconductors by a new modified TSIG technique

Single domain GdBCO bulk superconductors have been fabricated with new and traditional solid phases by a top seeded infiltration and growth (TSIG) process technique. In the conventional TSIG process, three types of powders, such as Gd2BaCuO5, GdBa2Cu3O7−x and Ba3Cu5O8, must be prepared, but in our new modified TSIG technique, only BaCuO2 powders are required during the fabrication of the single domain GdBCO bulk superconductors. The solid phase used in the conventional process is Gd2BaCuO5 instead of the solid phase (Gd2O3+BaCuO2) utilized in the new process. The liquid phase used in the conventional process is a mixture of (GdBa2Cu3O7−x+Ba3Cu5O8), and the liquid phase in the new process is a mixture of (Gd2O3+10BaCuO2+6CuO). Single domain GdBCO bulk superconductors have been fabricated with the new solid and liquid phases. The levitation force of the GdBCO bulk samples fabricated by the new solid phase is 28N, which is slightly higher than that of the samples fabricated using the conventional solid phases (26N). The microstructure and the levitation force of the samples indicate that this new method can greatly simplify the fabrication process, introduce nanometer-sized flux centers, improve the levitation force and working efficiency, and greatly reduce the cost of fabrication of single domain GdBCO bulk superconductors by the TSIG process.

Fabrication method of large size single domain GdBCO bulk superconductor using a new solid source

A new solid source was prepared and used to fabricate large size GdBCO single domain superconductor by top-seeded infiltration and growth (TSIG) process. The morphology, microstructure, and superconductivity properties of the GdBCO sample were investigated. It is found that the proposed solid source can be used to fabricate a well textured GdBCO single domain, and also reduce the fabrication cost and improve working efficiency. The results are helpful to fabricate high quality and large size single domain GdBCO bulk superconductors.

The effect of additional permanent magnet magnetizing methods on magnetic field distribution and the levitation force of single domain GdBCO bulk superconductor

It has been investigated that the interaction force between a cubic permanent magnet PM1 and a GdBCO bulk (HTSC) superconducting permanent magnet (SCPM) magnetized by a cubic permanent magnet PM2 under different configurations at 77 K. Two configurations were used for the magnetization of the GdBCO bulk, one is that the North pole of the PM2 is in upward direction, the other is in downward direction, so that the North pole of the SCPM is in two states SCPM↑ and SCPM↓; the vertical distance between the bottom surface of PM1 and the top surface of SCPM is kept as a constant value, but the PM2 can be fixed at any positions (x) along a diameter of the GdBCO bulk during the magnetization process. It is found that: for the PM1↓-SCPM↑ configuration, the maximum levitation force is increasing from 16.7 N to 23.1 N when x increases from –15 mm to 0, and then decreases to 16.6 N when x further increases to 15 mm; but for the PM1↓-SCPM↓ configuration, the maximum levitation force is decreasing from 17.7 N to 7 N when x increases from –15 mm to 0, and then increases to 17.6 N when x further increases to 15 mm. These results are not only much different in the two configurations, but also much different from the maximum levitation force 17.1 N of the sample under zero field cooled condition, which is closely related with the trapped field distribution of the SCPM at different x values. These results indicate that the levitation force of high temperature bulk superconductors can be effectively improved by introducing additional permanent magnet based on scientific and reasonable designing of the system configurations, which is very important during the practical design and applications of superconducting magnetic levitation systems.

The effects of magnetization methods with additional permanent magnet on the magnetic field distribution and levitation force of single domain GdBCO bulk superconductor

The effects of magnetization methods with additional permanent magnet on the magnetic field distribution and the levitation force of single domain GdBCO bulk superconductor are investigated with a cubic permanent magnet in their coaxial configuration in zero field cooled state at liquid nitrogen temperature in three different ways. It is found that when the N pole of the cubic permanent magnet, for the levitation force measurement, is placed above the GdBCO bulk superconductor and in the downward direction, the maximal levitation force can be improved to 31.8 N, and that when the N pole of the additional cubic permanent magnet points to upward and sticks to the bottom of the GdBCO bulk, the maximal levitation force is increased up to about 222% of the levitation force of 14.3 N for the system without additional permanent magnet. The maximal levitation force can be improved to 21.6 N (or reduced to 8.6 N), when the GdBCO bulk superconductor is closely placed below and magnetized by the additional cubic permanent magnet with N pole in the upward (or downward) direction, and the additional permanent magnet is removed away after the magnetization, the maximal levitation force is about 151% (or 60%) of 14.3 N for the system without the additional permanent magnet. The results indicate that the levitation force of high temperature bulk superconductors can be effectively improved by introducing additional permanent magnet based on the scientific and reasonable designing of the system configurations, which is very important for the practical design and application of superconducting magnetic levitation system.

Fabrication of single domain GdBCO bulks with different new kind of liquid sources by TSIG technique

Single domain GdBCO bulk superconductors have been fabricated with different new kinds of liquid sources by Top Seeded Infiltration and Growth process. A conventional liquid source is a mixture of REBa2Cu3O7−x and Ba3Cu5O8 in a ratio of 1:1; new liquid sources are made of a mixture of RE2BaCuO5+9BaCuO2+6CuO or RE2O3+10BaCuO2+6CuO. The microstructures and levitation forces of the GdBCO bulks have also been investigated. The properties of the samples fabricated are nearly the same as those of samples fabricated with conventional liquid sources, which indicates that the new liquid sources are very important to reduce the cost and improve the working efficient on the fabrication of single-domain GdBCO bulk superconductors.

Effect of assembled bar magnet configuration on levitation force of single domain GdBCO bulk superconductor

By measuring the levitation forces between a single domain GdBCO bulk superconductor and assembled bar magnets(ABM) in different configurations at liquid nitrogen temperature, the effects of ABM configurations on the levitation force of single domain GdBCO bulk superconductor are investigated. The maximum levitation force is obtained at the same vertical gap distance Z=5 mm between the superconductor and the ABM for configurations with different lateral gap distance(D)between the magnets of the ABM. It is found that 1) for the ABM consisting of 3 bar magnet, the levitation force of the GdBCO bulk decreases from 22.8N to 9.7N with the D value increasing from 0 to 30 mm, when the magnetic pole N of the middle magnet is pointed upwards and the directions of magnetic pole N of two side magnets are pointed to the middle magnet in horizontal direction; the levitation force of the GdBCO bulk increases first from 9.2N to 13.9N and then decreases to10.4 N with D value increasing from 0 to 30mm, if the magnetic pole N of the middle magnet is pointed upwards and the directions of magnetic pole N of two side magnets are pointed downwards;2)for the ABM consisting of 2 bar magnets, the levitation force of the GdBCO bulk decreases from 11.2N to 1.2N with D value increasing from 0 to 30mm, when the directions of magnetic pole N of two side magnets are pointed upwards; the levitation force of the GdBCO bulk increases first from 6.0N to 6.8N and then decreases to 2.9N with D value increasing from 0 to 30mm, if the directions of magnetic pole N of two magnets are anti-parallel in horizontal direction; 3)for the ABM consisting of only 1 bar magnets, D≡0, and the levitation force of the GdBCO bulk is about 9.5N. The results indicate that the magnet configuration and its detailed parameters of ABM are very important for improving the levitation force of a superconductor and helpful for designing and application based on the superconducting magnetic levitation system.

The effect of Gd<sub>2</sub>Ba<sub>4</sub>CuNbO<sub>y</sub> doping on the properties of single domain GdBCO bulk superconductors

Single domain GdBCO bulk superconductors, with compositions of GdBa 2 Cu 3 O 7-δ (Gd123):Gd 2 BaCuO 5 (Gd211): Gd 2 Ba 4 CuNbO y (GdNb2411) =1:(0.4-x):x, (x=0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16), have been successfully fabricated by the top-seeding melt texture growth process (TSMTG). The effect of the different doping amounts of GdNb2411 on the growth morphology and the magnetic levitation force properties of single domain GdBCO bulk superconductors has been investigated. The results show that single domain GdBCO bulk samples can be fabricated within the scope of the doping, and the surface morphologies of the samples are closely related to the doping content x. It is of a smooth faced plane and four clear radius for the samples with x≤0.06 mol, but it is of a wrinkle surface for the samples with x≥0.08mol and the single domain area is observed to reduce with the increasing of x. The test results of the magnetic levitation force of the samples show that the levitation force of samples increases first and then decreases with the increasing of x, the largest levitation force of 25 N is obtained in the samples with x=0.06 mol. The results is very important for study in flux pinning of nanoparticles and further improvement in the properties of GdBCO bulk superconductors.