Isotope shift of the ferromagnetic transition temperature in itinerant ferromagnets

Original · EN

We present a theory of the isotope effect of the Curie temperature T c in itinerant ferromagnets. The isotope effect in ferromagnets occurs via the electron-phonon vertex correction and the effective attractive interaction mediated by the electron-phonon interaction. The decrease of the Debye frequency increases the relative strength of the Coulomb interaction, which results in a positive isotope shift of T c when the mass M of an atom increases. Following this picture, we evaluate the isotope effect of T c by using the Stoner theory and a spin-fluctuation theory. When T c is large enough as large as or more than 100K, the isotope effect on T c can be measurable. Recently, precise measurements on the oxygen isotope effect on T c have been performed for itinerant ferromagnet SrRuO₃ with T c 160K. A clear isotope effect has been observed with the positive shift of T c 1K by isotope substitution (¹⁶O→ ¹⁸O). This experimental result is consistent with our theory.