Octahedral tilting and emergence of ferrimagnetism in cobalt-ruthenium based double perovskites

Abstract

Rare earth based cobalt-ruthenium double perovskites A2CoRuO6 (A = La, Pr, Nd and Sm) were synthesized and investigated for their structural and magnetic properties. All the compounds crystallize in the monoclinic P 21/n structure with the indication of antisite disorder between Co and Ru sites. While, La compound is already reported to have an antiferromagnetic state below 27 K, the Pr, Nd and Sm systems are found to be ferrimagnetic below Tc = 46, 55 and 78 K respectively. Field dependent magnetization data indicate prominent hysteresis loop below Tc in the samples containing magnetic rare-earth ions, however magnetization does not saturate even at the highest applied fields. Our structural analysis indicates strong distortion in the Co-O-Ru bond angle, as La 3+ is replaced by smaller rare-earth ions such as Pr 3+ , Nd 3+ and Sm 3+ . The observed ferrimagnetism is possibly associated with the enhanced antiferromagnetic superexchange interaction in the Co-O-Ru pathway due to bond bending. The Pr, Nd and Sm samples also show small magnetocaloric effect with Nd sample showing highest value of magnitude ∼ 3 Jkg −1 K −1 at 50 kOe. The change in entropy below 20 K is found to be positive in the Sm sample as compared to the negative value in the Nd counterpart.

A combined study on structural, magnetic and specific heat on double perovskite iridates Ln2CoIrO6 [Ln = Pr, Nd]

“…Moreover, the extent of such reversal gets minimized and eventually diminishes at much higher external fields. On comparing with other DPs where Ir 4+ is replaced by Mn 4+ (3d) and Ru 4+ (4d) that is Nd 2 CoMnO 6 and Nd 2 CoRuO 6 respectively, we see that the magnetization in FC mode increases with decrease in temperature with no sign of magnetic anomaly [26,33,34]. The temperature dependent inverse dc susceptibility for both the compounds are shown in supplement S5.…”

“…From the view point of magnetism, both the impurity phases, Other than 3d-Co (2+)-5d-Ir (4+) systems, such behavior has been identified in 3d-Co (2+)-4d-Ru (4+) system, where the observed ferrimagnetism originates from the strong deviation in Co-O-Ru bond angle and bond bending which ultimately leads to enhanced AFM superexchange interaction [26]. Similarly, the magnetic structures and the spin alignment of the 3d-Ni (2+)-3d-Mn (4+) system are also explained.…”

“…14) based on the Ln 2 NiIrO 6 structure data [25].The reliable factors obtained are, PCIO: R p = 17,R wp = 10, χ 2 = 2.89; NCIO: R p = 15, R wp = 10, χ 2 = 2.25. In general, the DP compounds are highly disordered in nature [26,27]. A careful Rietveld analysis of the XRD data shows an antisite disorder of ∼10% in PCIO and ∼7% in NCIO.…”

A-Site Modulation of Co–Ir Based Double Perovskite Oxides (A2CoIrO6, A = Sr, Nd, Pr, and Sm) for Maximization of Water Oxidation and Hybrid Electrolysis Derived Isopropanol Upconversion in Acid Medium

“…Thus, the Co and Ir octahedra gets tilted, which gives rise to the bending of the Co–O–Ir bond angle (∼150° for the Pr, Nd, and Sm based compounds) and a deviation from an ideal value of 180°. Moreover, for the lanthanide group, moving from Pr to Sm, the ionic radii decrease ( r Pr 3+ = 99 pm > r Nd 3+ = 98.3 pm > r Sm 3+ = 95.8 pm) due to lanthanide contraction; hence, the volume of the unit cell decreases, which also results in shorter Co–Ir bond distance (3.91 Å for PRCO, 3.886 Å for NDCO, 3.857 Å for SMCO, and 3.935 Å for SRCO). For the double perovskite A 2 BB′O 6 , one can define a Goldschmidt tolerance factor as follows: where r A and r O represent the ionic radius of A and O respectively and r B represents the average of ionic radii for atoms at B-site.…”

Structural, magnetic, magnetocaloric behavior and magneto-transport, electrical polarization study in 3d based bulk and nano-crystalline multiferroic double perovskite Dy2MnCoO6

“…This mismatch can be caused due to the presence of ASD, which reduces the magnetic moment. Approximately, we can calculate the presence of ASD in our sample by using [53]…”