Investigation of the influence of a magnetic field on the chemical potential of electrons in superconducting and ferromagnetic thin films

Abstract

It is experimentally shown that measurements of the chemical-potential variation in a magnetic field could give valuable information about the magnetization of thin films. For superconducting single-crystal ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ thin films two kinds of behavior of \ensuremath{\mu}(H) were observed depending on the substrate used. For films deposited on polished ${\mathrm{NdGaO}}_{3}$ single-crystal substrates the change of \ensuremath{\mu} was mainly reversible. That means that no magnetic flux was trapped during a magnetic-field sweep. For films deposited on MgO, ${\mathrm{SrTiO}}_{3}$, and ${\mathrm{LaAlO}}_{3}$ single-crystal substrates \ensuremath{\mu} changed irreversibly. The estimated critical current density is ${\mathit{j}}_{\mathit{c}}$\ensuremath{\sim}${10}^{7}$ A/${\mathrm{cm}}^{2}$ at T=4.2 K in both cases. Oscillations of \ensuremath{\mu} in films evaporated on cleaved MgO substrates were observed. The effect of a magnetic field on \ensuremath{\mu} in a ferromagnetic film, predicted 60 years ago, was confirmed.