Superconductivity and ferromagnetism are antagonistic types of ordering, and their mutual effects give rise to several interesting phenomena which have recently been studied in rare earth compounds. A theoretical analysis shows that while a ferromagnetic superconductor is a type II superconductor near the superconducting transition point $T_\mathrm{c1}$, it becomes a type I superconductor near the ferromagnetic transition point $T_\mathrm{M}$. A new theory derived for the case $T_\mathrm{M}\ll T_\mathrm{c1}$ predicts the formation of a transverse domain-like magnetic structure near $T_\mathrm{M}$. In clean superconductors the electron spectrum is gapless. A change in the behavior from type II to type I upon cooling to TM has been observed experimentally in ErRh$_4$B$_4$. Experimental data on ErRh$_4$B$_4$, HoMo$_6$Se$_8$ and HoMo$_6$Se$_8$ prove the existence of superconductivity and a magnetic ordering below $T_\mathrm{M}$.

RT Journal
T1 Magnetic superconductors
A1 Buzdin,A.I.
A1 Bulaevskii,L.N.
A1 Kulich,M.L.
A1 Panyukov,S.V.
PB Physics-Uspekhi
PY 1984
FD 10 Dec, 1984
JF Physics-Uspekhi
JO Phys. Usp.
VO 27
IS 12
SP 927-953
DO 10.1070/PU1984v027n12ABEH004085
LK https://ufn.ru/en/articles/1984/12/b/