| Autor: |
Najev, Ana, Hameed, Sajna, Alfonsov, Alexey, Joe, Joseph, Kataev, Vladislav, Greven, Martin, Požek, Miroslav, Pelc, Damjan |
| Rok vydání: |
2022 |
| Předmět: |
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| Zdroj: |
Phys. Rev. B 109, 174406 (2024) |
| Druh dokumentu: |
Working Paper |
| DOI: |
10.1103/PhysRevB.109.174406 |
| Popis: |
We present a nuclear magnetic resonance (NMR) and electron spin resonance (ESR) study of rare-earth titanates derived from the spin-1/2 Mott insulator YTiO$_3$. Measurements of single-crystalline samples of (Y,Ca,La)TiO$_3$ in a wide range of isovalent substitution (La) and hole doping (Ca) reveal several unusual features in the paramagnetic state of these materials. $^{89}$Y NMR demonstrates a clear discrepancy between the static and dynamic local magnetic susceptibilities, with deviations from Curie-Weiss behavior far above the Curie temperature $T_C$. No significant changes are observed close to $T_C$, but a suppression of fluctuations is detected in the NMR spin-lattice relaxation time at temperatures of about $3\times T_C$. Additionally, the nuclear spin-spin relaxation rate shows an unusual peak in dependence on temperature for all samples. ESR of the unpaired Ti electron shows broad resonance lines at all temperatures and substitution/doping levels, which we find to be caused by short electronic spin-lattice relaxation times. We model the relaxation as an Orbach process that involves a low-lying electronic excited state, which enables the determination of the excited-state gap from the temperature dependence of the ESR linewidths. We ascribe the small gap to Jahn-Teller splitting of the two lower Ti $t_{2g}$ orbitals. The value of the gap closely follows $T_C$ and is consistent with the temperatures at which deviations from Curie-Weiss fluctuations are observed in NMR. These results provide insight into the interplay between orbital and spin degrees of freedom in rare-earth titanates and indicate that full orbital degeneracy lifting is associated with ferromagnetic order. |
| Databáze: |
arXiv |
| Externí odkaz: |
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