Abstract
MgB2 films in four thickness (60 nm, 200nm, 600nm and 1μm) have been fabricated by hybrid physical–chemical vapor deposition technique (HPCVD). By measuring the magnetization hysteresis loops and the resistivity, we have obtained the transport and magnetic properties of the four films. After that, the pinning mechanisms in them were discussed. Comparing the pinning behaviors in these ultrathin films, thin films and thick films, it was found that there exist different pinning types in MgB2 films of different thickness. In combination with the study of the surface morphology, cross-section and XRD results, we concluded that MgB2 films had different growth modes in different growth stages. For thin films, films grew along c axis, and grain boundaries acted as surface pinning. While for thick films, films grew along c axis at first, and then changed to a-b axis growth. As a result, the a-b axis grains acted as strong volume pinning.
Highlights
Since the discovery of superconductivity in MgB2,1 a fair amount of research has been done in recent ten years due to its excellent superconducting properties
We focus on the study of the pinning mechanism in pure MgB2 films deposited by hybrid physical-chemical vapor deposition (HPCVD) on SiC substrates, and the relationship between pinning situations and thickness was discussed on a large scale, which covers ultrathin films, thin films and thick films
The transport properties were measured by standard four-terminal resistivity on a Quantum Design physical properties measurement system (PPMS), and the magnetization hysteresis loops were examined in a Quantum Design magnetic properties measurement system (MPMS) at 5K, 15K and 25K
Summary
Since the discovery of superconductivity in MgB2,1 a fair amount of research has been done in recent ten years due to its excellent superconducting properties. The critical current density Jc (0) at 5K of thin films reaches 107 A.cm-2.3 Combined with the low fabrication cost, MgB2 has become a promising superconductor. What’s more, compared with other methods (such as PLD, MBE and CVD), the MgB2 films possess better superconducting properties, and have been reported to be in the clean limit for thin films,[43] which have a potential to prepare SNSPDs. In addition, microstrip resonators based on double-side MgB2 thin films fabricated by HPCVD were prepared successfully,[44] and their microwave property is good, which show the potential applications for MgB2 films in microwave devices. Microstrip resonators based on double-side MgB2 thin films fabricated by HPCVD were prepared successfully,[44] and their microwave property is good, which show the potential applications for MgB2 films in microwave devices
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