Integer spin-chain antiferromagnetism of the 4$d$ oxide CaRuO${}_3$ with post-perovskite structure

A quasi-one-dimensional magnetism was discovered in the post-perovskite CaRuO${}_3$ (Ru${}^{4+}$: $4d^4$, Cmcm), which is isocompositional with the perovskite CaRuO${}_3$ (Pbnm). An antiferromagnetic (AFM) spin-chain function with −$J$/$k_{\mathrm{B}}$ $=$ 350 K reproduces the experimental curve of the magnetic susceptibility vs temperature well, suggesting long-range AFM correlations. The anisotropic magnetism is probably owed to the $d_{\mathit{yz}}$-$2p_{\mathrm{\pi }}$-$d_{\mathit{zx}}$ and $d_{\mathit{zx}}$-$2p_{\mathrm{\pi }}$-$d_{\mathit{yz}}$ superexchange bonds along the $a$ axis. The Sommerfeld coefficient of the specific heat is fairly small, 0.16(2) mJ mol${}^{-1}$ ${\mathrm{K}}^{-2}$, indicating that the magnetism reflects the localized nature of the 4$d$ electrons. This is an observation of an integer ($S$ $=$ 1) spin-chain AFM in the 4$d$ electron system.

Figure 1

Sketch of the crystal structures of (a) the Pv and (b) the PPv CaRuO${}_3$.[1] The figures used the same drawing scale. The PPv phase is $1.7\%$ denser in volume than the Pv phase.[1] The crystal structures are drawn by using vesta (Ref. 3).

Figure 2

$T$ vs ρ of a polycrystalline and dense ($d_{\mathrm{obs}}$/$d_{\mathrm{cal}}>0.97$) pellet of the PPv CaRuO${}_3$. The inset shows the Arrhenius plot of the data.

Figure 3

(Main panel) $C_{\mathrm{p}}$ vs $T$ and (upper inset) $C_{\mathrm{p}}$/$T$ vs $T$ ${}^2$ of the PPv CaRuO${}_3$.The lower inset shows an estimation of the transition entropy at ∼270 K.

Figure 4

(a) Low-temperature XRD patterns and (b) temperature dependence of the normalized lattice parameters of the PPv CaRuO${}_3$ (Cmcm). The 300-K parameters $a_0$ $=$ 3.115(1) Å, $b_0$ $=$ 9.826(1) Å, $c_0$ $=$ 7.297(1) Å, and $V_0$ $=$ 223.3(1) Å${}^3$ were used in the plot. The open triangles correspond to Si peaks. The broken line corresponds to the magnetic ordering temperature of the PPv CaRuO${}_3$, and the fat dotted curve indicates the $V$/$V_0$ curve for the Pv CaRuO${}_3$ (taken from Ref. 33).

Figure 5

$T$ dependence of the magnetic susceptibility of the PPv CaRuO${}_3$ measured at 50 kOe and a (solid curve) theoretical curve fitting to the data. Differential curve at the bottom indicates an anomaly at ∼270 K. (a.u. means arb. units.)

Figure 6

Thermal hysteresis of the magnetic susceptibility of the PPv CaRuO${}_3$ measured at (main panel) 1 kOe and (inset) 10 kOe.

Figure 7

Isothermal magnetization at various temperatures of the polycrystalline PPv CaRuO${}_3$. (f.u. stands for formula units.) The inset shows the data measured at 10 K.

Figure 8

Total density of states and PDOS for the PPv CaRuO${}_3$. We use a local coordinate system, which has a $z$ axis along the Ru-O1 bond and the $x$ axis approximately along the Ru-O2 bond. (a) Non-spin-polarized states, (b) AFM states.