Effect of Fe substitution on the magnetic ordering inCa3(Co1−xFex)2

Abstract

Mössbauer studies over 4.2-550 K of iron doped quasi-one-dimensional spin chain compounds Ca 3 ͑Co 1−x Fe x ͒ 2 O 6 , crystallizing in rhombohedral structure ͑space group R3c͒ for x ഛ 0.2, reveal that the iron resides only in the Co2 ͑6a͒ site. The compounds are paramagnetic at 90 K, and the iron exhibits slow spin relaxation phenomena even at room temperature. However, for the x = 0.5 compound, the crystal structure is triclinic ͑P1͒, and the iron resides almost equally in two different crystallographic sites and exhibits a very high magnetic ordering temperature T N ϳ 500 K. Both iron sites exhibit quadrupole interactions of almost equal size; however, with opposite sign ͑ 1 4 e 2 qQ Ϸ Ϯ 0.62 mm/ s ͒ . At T sr = 193 K, a spin reorientation of the iron magnetic moments is observed. Below 150 K the magnetic moments are tilted at 20°relative to the local electric field gradient axis and above 230 K they are aligned perpendicular to this axis. These results agree well with magnetic susceptibility measurements, in which a sharp drop in magnetization is observed above 200 K. The magnetic hyperfine fields in the two sites at 4.2 K are 53.3 and 45.7 T, respectively. The net magnetic interaction is antiferromagnetic, however, with a small ferromagnetic component displaying hysteresis along with a saturation magnetization of about 0.02 B / f.u. at 1.5 K.

Crystal structure, magnetic properties and ESR spectra of Ca3Co2−xFexO6

“…1, in agreement with the previous report on x = 1.0 (i.e., Ca 3 CoFeO 6 ) [15]. Note that space group P1 owns a very low symmetry and it is not possible to determine the structural details by Rietveld refinement because the initial positions of the atoms in the unit cell are not available in the literature [15]. Despite this deficiency, our XRD data shows that the dominant phase for samples with x = 0-0.7 is the rhombohedral structure, whereas that for x = 1.1-1.5 is the triclinic structure.…”

“…All the XRD patterns of x = 1.1-1.5 can be indexed in the triclinic structure (space group P1) with low-angle peaks marked in Fig. 1, in agreement with the previous report on x = 1.0 (i.e., Ca 3 CoFeO 6 ) [15]. Note that space group P1 owns a very low symmetry and it is not possible to determine the structural details by Rietveld refinement because the initial positions of the atoms in the unit cell are not available in the literature [15].…”

“…In this paper, we perform a systematic study on crystal structure and magnetic properties of Fe-doped compounds within x = 0-1.5, a concentration range much larger than that adopted in Refs. [14][15][16]. We find that the rhombohedral structure survives up to x = 0.7, which was not found before.…”

“…In recent years, Jain et al [14,15] reported the crystal structure and magnetic properties of Ca 3 Co 2−x Fe x O 6 with x = 0-0.4 and 1.0. It was found that Fe doping leads to a breaking of the FM linear spin chains and simultaneously introduces AFM exchange interaction between Fe 3+ irons.…”

“…Recalling that a FIM state has been observed in the Cr-and Mn-doped compounds [13,17], where both Cr and Mn tend to suppress the intrachain FM coupling and enhance the AFM coupling, it is expected that a similar FIM state exists in the Fe-doped compounds. In addition, the Fe-doped compounds reported earlier [14][15][16] were synthesized by traditional solid state method and no solubility limit was found. Compared to the solid state method, the sol-gel reaction method can achieve a mixture on the atomic level of the components, leading to a better crystallization.…”