Superconductivity and ferromagnetism in EuFe₂(As_1−xP_x)₂

Abstract

Abstract. Superconductivity and ferromagnetism are two antagonistic cooperative phenomena, which makes it difficult for them to coexist. Here we demonstrate experimentally that they do coexist in EuFe 2 (As 1−x P x ) 2 with 0.2 ≤ x ≤ 0.4, in which superconductivity is associated with Fe-3d electrons and ferromagnetism comes from the long-range ordering of Eu-4f moments via Ruderman-Kittel-KasuyaYosida (RKKY) interactions.The coexistence is featured by large saturated ferromagnetic moments, high and comparable superconducting and magnetic transition temperatures, and broad coexistence ranges in temperature and field. We ascribe this unusual phenomenon to the robustness of superconductivity as well as the multi-orbital characters of iron pnictides.(Some figures in this article are in colour only in the electronic version)

Magnetic structure of theEu2+moments in superconductingEuFe2(As1−xNandi1, Jin2, Xiao3 et al. 2014Phys. Rev. B407320View full textAdd to dashboardCite

“…However, the exact nature of the Eu 2+ magnetic order within the superconducting dome remained controversial [22]. Most surprising is the coexistence of ferromagnetism and superconductivity as recently proposed by many groups for the P-doped EuFe 2 As 2 samples [22][23][24][25][26]. In particular, Zapf et al [22,26] concluded based on macroscopic measurements that the Eu 2+ moments in EuFe 2 (As 1−x P x ) 2 order in a canted A-type antiferromagnetic structure with the spin component along the c direction being ferromagnetically aligned.…”

Coexistence of Bulk Superconductivity and Magnetism in CeO1−xFxBiS2

“…Furthermore, some compounds show superconductivity which coexist with long range magnetic ordering [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Since long range magnetic ordering usually competes against superconductivity, the materials possessing the coexistence of superconductivity and magnetism are of great interest for basic physics and applications.…”

Interplay between superconductivity and magnetism in Fe1−xPdxTe

“…Despite extensive investigations of interaction between SC and magnetic moments, there is so far no unified theory for the coexistence of SC and magnetism. With the lack of theoretic guidance, the existing experimental findings lead to two schools of thought: one is that both orders result from the same conduction electrons as evidenced by their synchronized magnetic and superconducting orders (22), and the other is that there are two separate sets of electrons responsible for magnetic ordering and superconductivity, respectively (19,21,25). What remains incomprehensible is the case where superconductivity and magnetic ordering coexist but are in competition with each other, as seen in Fe-based systems (23,24,27).…”

“…Although Fe is the most well known ferromagnet, all parent compounds of Fe-based superconductors exhibit AFM ordering. Though superconductivity is induced after suppressing the AFM ordering, it can coexist with either remaining AFM ordering (23,24,27) or new FM ordering (18,19), and this provides an ideal platform for studying the interplay between superconductivity and magnetism. Among the Fe-based superconductors, the chalcogenide FeTe 1−x Se x is unique in several aspects: (i) it is the only compound composed of slabs of Fe(Te/Se) 4 stacked together without an interlayer spacer; (ii) it becomes superconducting via isovalent doping of Se for Te, with the highest T c occurring at the 50% doping level; and (iii) the parent compound Fe 1+y Te shows nonmetallic electrical conduction and forms (π, π)-type AFM ordering with a large magnetic moment (28,29), in contrast to the (π, 0)-type ordering with a small magnetic moment seen in Fe pnictides.…”

“…Even though it is thought that Cooper pairs in cuprates, heavy fermions, and Fe-based compounds are mediated by spin fluctuations (3)(4)(5), SC generally occurs after suppressing the magnetic ordering either through chemical doping or the application of hydrostatic pressure (6)(7)(8)(9)(10). However, there is growing evidence for the coexistence of superconductivity with either ferromagnetic (FM) (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) or antiferromagnetic (AFM) ordering (21)(22)(23)(24). With the decrease of temperature (T), some of these systems show magnetic ordering before the superconducting transition (T c ) (14)(15)(16)(17)20), some are ordered in a reversed sequence (11-13, 18, 19, 22), some have the two orderings occur concomitantly (22,25), and some show reentrant superconductivity (partially) overlapping with a magnetically ordered phase (11)(12)(13)26).…”