Magnetic structure driven by monoclinic distortions in the double perovskite Sr₂YRuO₆

Abstract

The monoclinic double perovskite Sr 2 YRuO 6 has recently gained a renewed interest in order to get a deeper insight into the exotic magnetic ground states associated with geometric frustration. Striking discrepancies between the spin order derived from the neutron diffraction refinements and the macroscopic magnetic and thermal responses is a major challenge that must be addressed. In this work, detailed neutron diffraction measurements as a function of temperature yield a completely different interpretation of the patterns. We show that at low temperatures a spin structure of the K 2 NiF 4 -type is an accessible configuration for the magnetic ground state. In the neighborhood of the magnetic transition, this configuration evolves into a canted superstructure. The deduced temperature dependence of the canting angle exhibits two closely spaced peaks, which are in excellent agreement with the double peaks in the magnetic contribution to the specific heat and in the thermal expansion coefficient. We explain these features in terms of reorientation of the net ferromagnetic moment of the noncollinear spin state, due to the local breaking of the inversion symmetry promoted by the monoclinic distortions, with structural changes acting as the driving force.

Muon spin rotation and neutron scattering investigations of the B -site ordered double perovskite Sr2DyRuO6

“…It should be noted that there appear neither appreciable changes in the magnetic peak profiles nor new magnetic Bragg peaks in the temperature dependent data across the second anomaly (~36.5 K). In particular we did not detect any additional superlattice peak in the temperature region between TN1 and TN2, such as the one created by a propagation vector k = (½, ½, 0) found by Bernardo et al [36] in Sr2YRuO6. Furthermore there is no indication for short range correlations in the background below TN1 = 40 K. This indicates that the second transition might be associated with very small changes in the spin structure/spin reorientation which are beyond the detection limit even of the high intensity data.…”

“…Similar two anomalies/transitions were also reported for isostructural Sr2LnRuO6 (Ln=Y, Ho, Yb and Tb) and identified as antiferromagnetic ordering temperatures (TN2 and TN1). The anomalies were situated at 24 and 29 K for Y [36,37], 36 and 40 K for Yb [38], 32 and 26 K for Lu [46], and 15 and 36 K for Hobased systems [47]. On the other hand, the heat capacity study on the cubic Ba2DyRuO6 reveals only a single anomaly at 47 K [48], similar to La2NaRuO6 [11,41].…”

“…Among the antiferromagnetically ordered double perovskites, Sr2LnRuO6 (Ln = rare earth, Y, Ho, Yb and Lu etc.) compounds exhibit many interesting properties, for example the presence of two magnetic phase transitions and strong geometrical frustration above the magnetic ordering up to as high as 300 K, confirmed via heat capacity and inelastic neutron scattering measurements, respectively [36,37,38,39,40]. Recent neutron diffraction studies on Sr2YRuO6 reveal that at the first transition temperature only half of the Ru-layers order magnetically while the other half (alternatively) reveals short range ordering and below the second phase transition the system exhibits a type-I AFM ground state [37].…”

Spin dynamics and two-dimensional correlations in the fcc antiferromagneticSr2YRuO6

“…Finally, above T N 1 , a magnetically correlated state is observed, with significant correlations up to ∼ 300 K [11,22]. A second magnetic structure has been recently reported to occur between T N 1 and T N 2 [23], however no evidence of this state was observed in our previous detailed high-resolution diffraction study. [11].…”

Crystal and Magnetic Structures of La2CoPtO6 Double Perovskite

“…9−11 However, when the structural distortion is significant, the fcc network can become asymmetric, and thus, the magnetic order can be reinstated. 12,13 Indeed, it has been observed in DPs with various A ions that the spin ordering is associated with the structural distortion, which is tunable due to different ionic sizes of the A site ions. 1…”