First order valence transition: Neutron diffraction, inelastic neutron scattering and x-ray absorption investigations on the double perovskite Ba2PrRu0.9Ir0.1O6
| Autor: | Sannigrahi, J, Adroja, D, Ritter, C, Kockelmann, W, Hillier, A, Knight, K, Boothroyd, A, Wakeshima, M, Hinatsu, Y, Mosselmans, J, Ramos, S |
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| Rok vydání: | 2019 |
| Předmět: | |
| ISSN: | 2469-9950 |
| DOI: | 10.48550/arxiv.1903.11096 |
| Popis: | Bulk studies have revealed a first-order valence phase transition in Ba$_2$PrRu$_{1-x}$Ir$_x$O$_6$ ($0.10 \le x \le 0.25$), which is absent in the parent compounds with $x = 0$ (Pr$^{3+}$) and $x =1$ (Pr$^{4+}$), which exhibit antiferromagnetic order with transition temperatures $T_{\rm N} = 120$ and 72 K, respectively. In the present study, we have used magnetization, heat capacity, neutron diffraction, inelastic neutron scattering and x-ray absorption measurements to investigate the nature of the Pr ion in $x =0.1$. The magnetic susceptibility and heat capacity of $x =0.1$ show a clear sign of the first order valence phase transition below 175 K, where the Pr valence changes from 3+ to 4+. Neutron diffraction analysis reveals that $x =0.1$ crystallizes in a monoclinic structure with space group $P2_1/n$ at 300 K, but below 175 K two phases coexist, the monoclinic having the Pr ion in a 3+ valence state and a cubic one ($Fm\overline{3}m$) having the Pr ion in a 4+ valence state. Clear evidence of an antiferromagnetic ordering of the Pr and Ru moments is found in the monoclinic phase of the $x = 0.1$ compound below 110 K in the neutron diffraction measurements. Meanwhile the cubic phase remains paramagnetic down to 2 K, a temperature below which heat capacity and susceptibility measurements reveal a ferromagnetic ordering. High energy inelastic neutron scattering data reveal well-defined high-energy magnetic excitations near 264 meV at temperatures below the valence transition. The high energy excitations are assigned to the Pr$^{4+}$ ions in the cubic phase and the low energy excitations to the Pr$^{3+}$ ions in the monoclinic phase. Further direct evidence of the Pr valence transition has been obtained from the x-ray absorption spectroscopy. Comment: 10 pages and 10 figures |
| Databáze: | OpenAIRE |
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