Theoretical sensitivity limits of the compensation method for magnetization characteristics measurement of HTc superconducting materials using LTc SQUID 2nd order gradiometer
✍ Scribed by Vladimı́r Zrubec
- Publisher
- Elsevier Science
- Year
- 1999
- Tongue
- English
- Weight
- 246 KB
- Volume
- 39
- Category
- Article
- ISSN
- 0011-2275
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✦ Synopsis
This article deals with theoretical analysis of a fast compensation method of measuring magnetization characteristics using superconductive quantum 2nd order gradiometer suitable for measuring material samples with low magnetic susceptibility in an alternating low-frequency magnetic field. Special attention is paid to measuring magnetization characteristics of HT c superconductors at a temperature of 78K. Transmission and noise properties of the measuring system consisting of LT c SQUID 2nd order gradiometer and magnetization coil system with the sample of HT c superconductive material placed in liquid nitrogen in an external case under an LHe cryostat of a gradiometer are studied. The maximum sensitivity of the system given by noise properties of a superconductive quantum gradiometer, noise parameters of the magnetization magnetic field and environmental noise in the measuring environment is determined. It follows from a theoretical analysis that the spectral density limit of an input equivalent noise magnetic moment of a system placed in a magnetically shielded room with parameters achieved in rooms designed for measuring biomagnetic fields can reach the order of 10 -13 Am 2 Hz -1/2 . Under conditions typical of unshielded magnetic laboratories for measuring weak magnetic fields the order of (10 -8 ÷ 10 -11 ) Am 2 Hz -1/2 can be achieved theoretically. The measuring process is outlined and parameters achieved with systems in an unshielded environment and examples of measured characteristics of HT c superconductors in an alternating magnetization magnetic field with the frequency 0.1 Hz are cited. The accessibility of a sample for manipulation, general arrangement and a simple measuring process allow quick scanning and recording of magnetization characteristics (a set of five amplitude phased hysteretic curves in a time of ෂ 2.5 min).