Multiple magnetic orders discovered in the superconducting state of EuFe2(As 1−x P x)2

Abstract

The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe₂As₂-based iron pnictides could offer an interesting plateau to study their relationship that has attracted considerable attention. So far, two magnetic phase transitions were observed in EuFe₂As₂-based crystal, which were deemed to originate from the itinerant Fe moments (~190 K) and the localized Eu²⁺ moments (~19 K), respectively. Here, we systematically studied the heat capacity for the EuFe₂(As 1−xP_x)₂ crystals with x = 0.21 (optimally doped) and x = 0.29 (overdoped). We have found two new magnetic orders in the superconducting state (ranging from 0.4 to 1.2 K) in the optimally doped crystal. As more P was introduced into the As site, one of the magnetic orders becomes absent in the overdoped crystal. Additionally, we observed strong field and orientation dependence in heat capacity. The present findings in EuFe₂(As 1−xP_x)₂ have detected the new low-temperature magnetic orders, which may originate from the localized Eu²⁺ spins order or the spin reorientation.