Exotic Magnetism in Perovskite ${\mathrm{KOsO}}_3$

A new perovskite ${\mathrm{KOsO}}_3$ has been stabilized under high-pressure and high-temperature conditions. It is cubic at 500 K ($Pm-3m$) and undergoes subsequent phase transitions to tetragonal at 320 K ($P4/mmm$) and rhombohedral ($R-3m$) at 230 K as shown from refining synchrotron x-ray powder diffraction (SXRD) data. The larger orbital overlap integral and the extended wave function of 5d electrons in the perovskite ${\mathrm{KOsO}}_3$ allow to explore physics from the regime where Mott and Hund’s rule couplings dominate to the state where the multiple interactions are on equal footing. We demonstrate an exotic magnetic ordering phase found by neutron powder diffraction along with physical properties via a suite of measurements including magnetic and transport properties, differential scanning calorimetry, and specific heat, which provide comprehensive information for a system at the crossover from localized to itinerant electronic behavior.

Figure 1

(a) Lattice parameters versus temperature for ${\mathrm{KOsO}}_3$ obtained by Rietveld refinement of the synchrotron XRD profile ($\lambda =0.61928\AA$) collected on warming and cooling processes. The data acquired from warming up are denoted by red markers, while data from cooling down are represented by blue markers. (b) Neutron powder diffraction (ND), synchrotron x-ray diffraction at 500 K, and the fitting results of ND (the reflections from top to bottom represent nuclear structure of ${\mathrm{KOsO}}_3$, nuclear structure of Os, and magnetic structure of ${\mathrm{KOsO}}_3$); the inset is the spin structure from the fitting. (c) The zoomed-in plot of ND and the simulation.

Figure 2

(a) Field dependence of the magnetization of ${\mathrm{KOsO}}_3$ at different temperatures; temperature dependences of (b) the magnetization, (c) the resistivity, (d),(f) the specific heat, and (e) the thermoelectric power. The symbols in (c) represent the results measured on a cluster of ${\mathrm{KOsO}}_3$ crystal (WU, warm up; CD, cool down); the solid line shows the result of pressed powder sample in a diamond anvil cell.

Figure 3

(a),(b) The correlation between the Néel temperature ${\mathrm{T}}_{\mathrm{N}}$ and the magnetic moment at 4.2 K and the structural distortion in the perovskite structure for the 3d, 4d, and 5d perovskites with the ${\mathrm{t}}_{2\mathrm{g}}^3{\mathrm{e}}_{\mathrm{g}}^0$ electronic configuration. The angle $\varphi$ measures the deviation of bond angle $\mathrm{M}─\mathrm{O}─\mathrm{M}$ from 180º in the orthorhombic perovskite structure. $A$ in the formula stands for alkaline elements, AE for alkaline earth elements, and $R$ for rare-earth elements. The magnetic moments in ${\mathrm{RCrO}}_3$ are from Ref. [37]; the moment of ${\mathrm{SrMnO}}_3$ at 77 K is from Ref. [36], which is converted to the moment at 4.2 K following the Brillouin function ($\mathrm{J}=3/2$); the moment of ${\mathrm{Ca}}_{1-\mathrm{x}}{\mathrm{Sr}}_{\mathrm{x}}{\mathrm{MnO}}_3$ is from Ref. [3]; the moment of ${\mathrm{CaTcO}}_3$ is from Ref. [38]; the moment of ${\mathrm{SrTcO}}_3$ is from Ref. [5]; the moment of ${\mathrm{NaOsO}}_3$ at 200 K is from Ref. [8], which is converted to the moment at 4.2 K following the Brillouin function ($\mathrm{J}=3/2$). (c) A schematic phase diagram shows the evolution of the magnetic transition temperature as a function of electron bandwidth from localized electrons to itinerant electrons.