High Temperature Magnetic Ordering in the $4d$ Perovskite ${\mathrm{SrTcO}}_3$

We present evidence for possibly the highest magnetic ordering temperature in any compound without $3d$ transition elements. Neutron powder diffraction measurements, at both time-of-flight and constant wavelength sources, were performed on two independently prepared ${\mathrm{SrTcO}}_3$ powders. ${\mathrm{SrTcO}}_3$ adopts a distorted perovskite structure with $G$-type antiferromagnetic ordering and has a moment of $1.87(4){\mu }_B$ per Tc cation at room temperature with an extraordinarily high Néel point close to $750°\mathrm{C}$. Electronic structure calculations reveal extensive mixing between the technetium $4d$ states and oxygen states proximal to the Fermi level. This hybridization leads to a close relationship between magnetic ordering temperature and moment formation in ${\mathrm{SrTcO}}_3$.

Figure 1

(a) Observed constant wavelength NPD profiles of ${\mathrm{SrTcO}}_3$; select $2\theta$ regions are shown to highlight the change from $Pnma$ symmetry to $Pm\overline{3}m$ symmetry and the loss of the magnetic peak at 19.4° $2\theta$ upon heating. Tick marks for the cubic and orthorhombic structures are shown below the patterns, respectively. (b) Simulated contributions to the NPD patterns from the nuclear $Pnma$ and $Pm\overline{3}m$ structures and the magnetic $P{n}^{\prime }m{a}^{\prime }$ structure. (c) Temperature evolution of the magnetic peak from the CW data.

Figure 2

(a) $G$-type antiferromagnetic ordering in the orthorhombic unit cell used for the structural refinement with the NPD data. (b) The $A$-type antiferromagnetic ordering and (c) $C$-type ordering. The sublattice with sides $\approx a_p$ [light gray (orange) line] corresponding to the cubic perovskite is drawn within the orthorhombic cells (thin dashed line).

Figure 3

(a) Electronic DOS and projections onto LAPW spheres for non-spin-polarized ${\mathrm{SrTcO}}_3$. (b) Electronic DOS and majority and minority spin $d$ projections onto the Tc LAPW sphere for $G$-type ${\mathrm{SrTcO}}_3$.