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首页> 外文期刊>Physica, B. Condensed Matter >Effect of annealing temperature on some physical properties of MgB_2by using the Hall probe ac-susceptibility method
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Effect of annealing temperature on some physical properties of MgB_2by using the Hall probe ac-susceptibility method

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A commercially available powder of MgB_2is used as starting material for the examination of theinfluence of the annealing temperature on the properties of this intermediate-T_csuperconductor. Weperformed scanning electron microscopy (SEM) and Hall ac-susceptibility measurements as a functionof temperature and ac-field amplitude on samples annealed at 650, 750, 850 and 950 ℃. The imaginarypart of ac-susceptibility measurements is used to calculate both the inter-granular critical currentdensity,Jc(Tp) and density of pinning force, aj(0). It was observed that all Tc,Jc(Tp) and αj(0) exhibit a non-monotonic behavior on the annealing temperature range studied in this work. Ic is measured to be39.85±0.02 K and Jc(Tp) is estimated to be as high as 60 A/cm2 at 39.2 K for the sample annealed at850℃. The peak temperature, Tp, in the imaginary part of the ac-susceptibility curves shifts to lowertemperatures with both decreasing the annealing temperature and increasing the amplitude of theac-magnetic fields. A comparison of the experimental ac-susceptibility data with theoretical critical-state models that are currently available is performed. SEM investigations showed that the grain sizeincreases, and the grain connectivity improves when the annealing temperature increases up to 850 ℃.The possible reasons for the observed changes in transport, microstructure and magnetic properties dueto annealing temperature are discussed.

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