Multiple magnetic orders discovered in the superconducting state of EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$

TL;DR

This study reveals new low-temperature magnetic orders in EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ superconductors, showing how doping influences magnetic phases and their interaction with superconductivity.

Contribution

It reports the discovery of multiple magnetic orders in the superconducting state of EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$, highlighting doping-dependent magnetic phase evolution.

Findings

Two new magnetic orders found in optimally doped crystals.

One magnetic order disappears in overdoped samples.

Strong field and orientation dependence observed in heat capacity.

Abstract

The interplay between superconductivity and magnetism is an important subject in condensed matter physics. EuFe$_{2}$As$_{2}$-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 EuFe$_{2}$As$_{2}$-based crystal, which were deemed to originate from the itinerant Fe moments ($\sim$ 190 K) and the localized Eu$^{2+}$ moments ($\sim$ 19 K), respectively. Here, we systematically studied the heat capacity for the EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ crystals with \textit{x} = 0.21 (optimally doped) and \textit{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 EuFe$_{2}$(As$_{1-x}$P$_{x}$)$_{2}$ have detected the new low-temperature magnetic orders, which may originate from the localized Eu$^{2+}$ spins order or the spin reorientation.