Crystallographic and magnetic properties of the mixed-valence oxidesCaRu1−xMnxO3

Abstract

The crystallographic and magnetic properties of CaRu 1−x Mn x O 3 ͑0 Յ x Յ 1.0͒ were investigated in detail by x-ray powder diffraction, magnetization, and magnetic Compton scattering measurements. The lattice parameters show considerable deviation from Vegard's law. Ferromagnetism appears at a relatively large Mn concentration ͑x Ն 0.2͒, and the magnetization and the Curie temperature have a maximum at a Mn content near x = 0.7. The magnetic Compton scattering measurement revealed that Mn makes a dominant contribution to the magnetization and the Mn moment is antiparallel to the Ru moment, which is induced by Mn doping. The anomalous change in the unit cell volume and the occurrence of ferromagnetism were discussed on the basis of the mixed-valence model of Mn 3+ , Mn 4+ , Ru 4+ , and Ru 5+ ions. The Mn-composition dependence of the spontaneous magnetization was explained semiquantitatively assuming ͑1͒ ferromagnetic coupling between Mn 3+ and Mn 4+ ions, ͑2͒ antiferromagnetic coupling between Ru 5+ and Mn ions, and ͑3͒ the theoretical spin moments of Mn 3+ , Mn 4+ , and Ru 5+ . The ferromagnetic interaction between Mn 3+ and Mn 4+ ions seems to make a dominant contribution to the Curie temperature. The CaRu 1−x Mn x O 3 system is considered to be a ferrimagnet induced through competition between the ferromagnetic interaction between Mn ions and the antiferromagnetic interaction between Ru 5+ and Mn ions.

Electrochemical crystal growth of perovskite ruthenates

“…The data of CaRuO 3 could be refined by assuming an orthorhombic structure of the space group Pnma and the lattice constants of a ¼ 5.5324(4) Å , b ¼ 7.6640(5) Å , and c ¼ 5.3563(4) Å . These values agree well with those given in previous studies [4,[11][12][13]. The data of SrRuO 3 could be refined by assuming a cubic structure of the space group Pm3m and a lattice constant of a ¼ 3.9229(1) Å .…”

“…SrRuO 3 is known as a metallic ferromagnet with a Curie temperature T C of 160 K, but no magnetic order could be found in CaRuO 3 at temperatures down to 0.3 K in spite of the negative asymptotic Curie temperature deduced from the data at high temperatures [1][2][3][4]. However, it has been reported that a very small substitution on the Ru site induced ferromagnetism in CaRuO 3 [5][6][7].…”

Transport and Thermoelectric Properties of the Ca1−x Sr x Ru1−y Mn y O3 System

“…The possible coexistence of Ru 4+ , Ru 5+ , Mn 3+ , and Mn 4+ ions has been reported to explain the ferromagnetism observed in the CaRu 1Àx Mn x O 3 system. 13 Therefore, the ferromagnetism observed in the Ca 0.5 Sr 0.5 Ru 1Ày Mn y O 3 system should be attributed to the ferromagnetic exchange interaction between Mn 3+ and Mn 4+ ions. Moreover, a magnetic Compton scattering study on the CaRu 1Àx Mn x O 3 system revealed that the Mn spin moments are antiparallel to the Ru spin moments and that Mn makes a dominant contribution to the magnetization.…”

“…This behavior has been explained assuming a mixed-valence state of Ru 4+ , Ru 5+ , Mn 3+ , and Mn 4+ ions. 13 Figure 2a shows the temperature dependence of the magnetization measured for specimens of Ca 0.5 Sr 0.5 Ru 1Ày Mn y O 3 (0 £ y £ 1.0) under an applied field of 1 kOe. The thermomagnetic curves M(T) of specimens with low Mn content (x < 0.2) show ferromagnetic behavior with lower T C , near 50 K. The ferromagnetism of the specimens with low Mn content seems to originate due to a mechanism similar to that of the ferromagnetism in SrRuO 3 .…”

Linking local structure and properties in perovskites containing equal concentrations of manganese and ruthenium

“…6 It is therefore not surprising that perovskites which contain both Mn and Ru have also attracted considerable interest. [7][8][9][10][11][12][13][14][15] The physical properties of these compounds are primarily governed by the oxidation states of the Mn and Ru cations, which often exist in a state of mixed valency. The properties of these materials can be tuned by controlling the ratio of Mn to Ru and also by manipulating the charge and/or size of the cations on the A-site.…”