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A magnetization and $^{11}$B NMR study of Mg$_{1-x}$Al$_x$B$_2$ superconductors

M. Pissas·G. Papavassiliou·M. Karayanni·M. Fardis·I. Maurin·I. Margiolaki·K. Prassides·C. Christides
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Abstract

We demonstrate for the first time the magnetic field distribution of the pure vortex state in lightly doped Mg$_{1-x}$Al$_x$B$_2$ ($x\leq 0.025$) powder samples, by using $^{11}$B NMR in magnetic fields of 23.5 and 47 kOe. The magnetic field distribution at T=5 K is Al-doping dependent, revealing a considerable decrease of anisotropy in respect to pure MgB$_2$. This result correlates nicely with magnetization measurements and is consistent with $σ$-band hole driven superconductivity for MgB$_2$.

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M. Pissas, G. Papavassiliou, M. Karayanni, M. Fardis, I. Maurin, I. Margiolaki, K. Prassides, C. Christides. 2001-11-19. A magnetization and $^{11}$B NMR study of Mg$_{1-x}$Al$_x$B$_2$ superconductors. https://doi.org/10.1103/physrevb.65.184514

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