High Temperature Magnetic Ordering in the4dPerovskiteSrTcO3

Abstract

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 SrTcO3 powders. SrTcO3 adopts a distorted perovskite structure with G-type antiferromagnetic ordering and has a moment of 1.87(4)μB per Tc cation at room temperature with an extraordinarily high Néel point close to 750 °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 SrTcO3.

Electronic structure and weak itinerant magnetism in metallicY2Ni7

“…We note that the Stoner model of itinerant magnetism has a parallel in the Slater model of itinerant antiferromagnetism and that high ordering temperatures in certain antiferromagnets have been discussed in a way similar to the above. [45][46][47] In neither case (itinerant or local moment magnets) can energy differences by themselves be simply interpreted as the ordering temperature.…”

Diffuse magnetic neutron scattering in the highly frustrated double perovskiteBa2YRuO6

“…This is often considered to be the most important contribution to a reduced moment 8,9 , but is difficult to quantify without detailed calculations of the electronic structure. Geometric frustration is also often invoked in the context of persistence of spin fluctuations to very low temperatures, but is even more difficult to quantify.…”

Itinerant Antiferromagnetism in RuO2

“…Both high-T N compounds share another important feature, namely the existence of a 4d 3 electron configuration. Since at T N SrTcO 3 has the ideal perovskite symmetry (space group Pm3m) [30], the three t 2g orbitals are degenerate and thus half-filled. In SrRu 2 O 6 the RuO 6 octahedra are stretched along the c-axis, but the C 3v symmetry still protects the t 2g orbital degeneracy [31].…”

“…Hence the specific crystal field splitting of the edge-shared octahedra in the rutile structure ensures that the 4d xz and 4d yz t 2g orbitals that are relevant for the AFM order are formally half filled, similar to SrTcO 3 and SrRu 2 O 6 . An important distinction, however, is that RuO 2 is a good metal whereas SrTcO 3 is theoretically predicted to be insulating [2,30] and SrRu 2 O 6 has been determined to be semiconducting from resistivity measurements. [5] The unique combination of good metallicity and high temperature AFM in RuO 2 will allow for a more complete benchmarking of theoretical models describing the interplay between magnetism and metallicity in oxide materials.…”

“…In the 4d series, the ruthenates Ca 3 Ru 2 O 7 and Na-doped CaRuO 3 (T N = 70 K) display antiferromagnetism at T N = 56 and 70 K, respectively, significantly lower than that of RuO 2 [28,29], and they are borderline insulating. Indeed, the recent discoveries of AFM with high T N in 4d transition metal oxides were made in semiconducting SrRu 2 O 6 (T N = 563 K) [5] and SrTcO 3 (T N = 1023 K) [30]; the latter is theoretically predicted to be insulating. [2,30] While the debate on itinerant versus localized magnetism in metallic systems [22,23] shows that it is difficult to determine the role of itineracy in AFM order, the robust metallicity, small moment, and high magnetic ordering temperature of RuO 2 places it in a regime that was hitherto not accessible in transition metal oxides.…”