Magnetic-crystallographic phase diagram of the superconducting parent compound Fe1+xTe

Abstract

Through neutron diffraction experiments, including spin-polarized measurements, we find a collinear incommensurate spin-density wave with propagation vector k = (0.4481(4) 0 1 2 ) at base temperature in the superconducting parent compound Fe1+xTe. This critical concentration of interstitial iron corresponds to x ≈ 12% and leads crystallographic phase separation at base temperature. The spin-density wave is short-range ordered with a correlation length of 22(3)Å, and as the ordering temperature is approached its propagation vector decreases linearly in the H-direction and becomes long-range ordered. Upon further populating the interstitial iron site, the spin-density wave gives way to an incommensurate helical ordering with propagation vector k = (0.3855(2) 0 1 2 ) at base temperature. For a sample with x ≈ 9(1)%, we also find an incommensurate spin-density wave that competes with the bicollinear commensurate ordering close to the Néel point. The shifting of spectral weight between competing magnetic orderings observed in several samples is supporting evidence for the phase separation being electronic in nature, and hence leads to crystallographic phase separation around the critical interstitial iron concentration of 12%. With results from both powder and single crystal samples, we construct a magnetic-crystallographic phase diagram of Fe1+xTe for 5% < x < 17%.

Magnetic order tuned by Cu substitution in Fe1.1−zCuzTe

“…11,25,28 For y < y c ≈ 0.1, the structure is monoclinic, with two different Fe-Fe in-plane bond lengths that match up with the alternating antiferromagnetic and ferromagnetic bonds of the collinear magnetic structure. 11,18,41 For y > y c , the structure is orthorhombic, with a single Fe-Fe bond length; the corresponding magnetic structure is found to be helical.…”

“…11,18,41 For y > y c , the structure is orthorhombic, with a single Fe-Fe bond length; the corresponding magnetic structure is found to be helical. 11, 25 Mizuguchi et al 28 have recently demonstrated with high-resolution x-ray diffraction that the boundary between the orthorhombic and monoclinic phases can also be crossed as a function of temperature for y y c . On cooling from the tetragonal phase, it is possible to transform first to the orthorhombic and then to the monoclinic.…”

“…Specifically, the order changes as y increases through the critical excess Fe content, y c , from bicollinear commensurate to helical incommensurate. 11,12,[25][26][27] The change in magnetic order correlates with the change in the low-temperature structural symmetry from monoclinic to orthorhombic. 25,28 The precise value of y c depends on whether it is de-termined chemically from the total Fe content or by refinement of neutron diffraction data.…”

“…11,12,[25][26][27] The change in magnetic order correlates with the change in the low-temperature structural symmetry from monoclinic to orthorhombic. 25,28 The precise value of y c depends on whether it is de-termined chemically from the total Fe content or by refinement of neutron diffraction data. 25,26 For comparison with the present work, the relevant value is y c ≈ 0.1.…”

“…25,28 The precise value of y c depends on whether it is de-termined chemically from the total Fe content or by refinement of neutron diffraction data. 25,26 For comparison with the present work, the relevant value is y c ≈ 0.1. 26 The nature of the magnetic order in the 11 system has been controversial.…”