Probing the magnetic ground state and magnetoelastic coupling in double perovskite ruthenate: Ca2ScRuO6

TL;DR

This study deciphers the magnetic ground state of Ca$_{2}$ScRuO$_{6}$, a 4d^3 double perovskite ruthenate, revealing a weak Type-I antiferromagnetic order (k = $(0,0,1)$) with a reduced moment of about $1.1$ μB per Ru$^{5+}$ alongside small Ru$^{4+}$-bearing clusters, driven by approximately $14 heta$ antisite disorder that induces Ru valence mixing. A combination of PXRD/NPD, XAS, dc/ac magnetization, heat capacity, resistivity, SXAS, and neutron scattering demonstrates long-range order coexisting with nanoscale magnetic inhomogeneity and moderate magnetoelastic coupling near the ordering temperature around $T_N \uparrow 40$ K. The material behaves as a Mott insulator with 3D variable-range hopping and shows a broad magnetic entropy release, consistent with short-range correlations riding on a long-range AFM lattice. Overall, Ca$_{2}$ScRuO$_{6}$ provides a unique platform to study how antisite disorder and mixed-valence Ru moments shape long-range magnetic order in a 4d^3 DP ruthenate, with potential implications for understanding magnetism in related oxide systems.

Abstract

Ruthenates, materials with a single magnetic Ruthenium (Ru) atom, often display an exotic array of ground states ranging from superconductivity to altermagnetism. In this work, we investigated the magnetic ground state of a least explored member of the 4d3 double perovskite ruthenate series A2ScRuO6 (A = Ca, Sr, Ba): Ca2ScRuO6. Interestingly, temperature-dependent bulk susceptibility curve shows ferrimagnetic-like behaviour above the magnetic ordering at around 40 K, which were corroborated by the identification of the mixed valence states, Ru5+ and Ru4+ via X-ray absorption spectroscopy. Structural analysis further revealed atomic-site exchange between the Ru and Sc sites, which results in the Ru mixed valence states. Neutron powder diffraction measurements detected the presence of magnetic Bragg peaks at a low temperature near 4 K and a moderate magnetoelastic coupling near the ordering temperature of 40 K. However, the corresponding symmetry analysis shows a weak Type I antiferromagnetic ground state with a reduced magnetic moment of 1.1μB/Ru atom. Our findings establish an unusual magnetic ground state in the Mott insulating Ca2ScRuO6, where a long range ordered antiferromagnet coexists with small magnetic clusters, which manifests a ferrimagnetic-like high temperature inverse magnetic susceptibility. This system presents a unique platform to study long-range magnetic order in the presence of antisite disorder.

Figures (14)

• Figure 1: Neutron powder diffraction pattern of Ca$_{2}$ScRuO$_{6}$ at 300 K (PD-II Data). The observed and calculated diffraction patterns are shown by the filled circles (red) and solid lines (black), respectively. The difference between observed and calculated patterns is shown by the thin line (blue) at the bottom of the panel. The vertical bars (green) are the allowed Bragg peak positions.
• Figure 2: Background subtracted Ru M$_{2,3}$-edge XANES spectra of RuO$_2$ and Ca$_2$ScRuO$_6$ compounds measured at room temperature.
• Figure 3: (a) $1 /\chi_M$$vs.$$T$ data of Ca$_{2}$ScRuO$_{6}$ at an external magnetic field, H = 1000 Oe (black circles). The red curve represents a ferrimagnetic like behaviour. The dashed blue line is the paramagnetic CW fit. Inset (i) shows the $\chi _{M}$$vs.$$T$ and $\frac{d(\chi _{M}T)}{dT} vs. T$ and inset (ii) shows the low field ($H = 100 Oe$) magnetization data ($\chi _{M}$$vs.$$T$)in ZFC and FC. (b) Field dependent magnetization ($M$$vs.$$H$) data for Ca$_{2}$ScRuO$_{6}$ at 2K and 100K.(c) Temperature variation of real part of ac magnetic susceptibility ($\chi^{'}$$vs.$$T$) at different frequencies.
• Figure 4: Temperature dependent heat capacity measurement( $C_p$$vs.$$T$) of Ca$_{2}$ScRuO$_{6}$ at an external field $H = 0~kOe$. Inset shows $C_{mag}$$vs.$$T$.
• Figure 5: (a) Temperature evolution of neutron diffraction patterns measured from 10K to 300K. (b-f) Thermal variations of lattice constants $a$, $b$, $c$, $V$ and $\beta$ of Ca$_{2}$ScRuO$_{6}$ from 10 to 300 K.