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論文

Schottky specific heat of the lightly Mn-substituted electron-doped SrTiO$$_3$$

奥田 哲治*; 梶本 亮一; 野田 正亮*; 桑原 英樹*

AIP Advances (Internet), 8(10), p.101339_1 - 101339_5, 2018/10

Large changes in the low-temperature specific heat (low-$$TC$$) by applying magnetic fields up to 9 Tesla were found in the lightly Mn-substituted electron-doped perovskites Sr$$_{1-x}$$La$$_{x}$$TiO$$_{3}$$. The changes in the low-$$TC$$ are qualitatively well explained by the Schottky specific heat ($$C_mathrm{Sch}$$) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. According to the analysis by using the conventional model, the doped Mn ions are apparently not Mn$$^{4+}$$ ($$S$$ = 3/2) ions, but are Jahn-Teller active Mn$$^{3+}$$ ($$S$$ = 2) ions or mixtures of Mn$$^{3+}$$ and Mn$$^{2+}$$ ions. However, the actual numbers of localized spins estimated from $$C_mathrm{Sch}$$ are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons, leading to the observed enhancement of the electronic specific heat coefficients.

論文

Elastic and dynamical structural properties of La and Mn-doped SrTiO$$_{3}$$ studied by neutron scattering and their relation with thermal conductivities

梶本 亮一; 中村 充孝; 村井 直樹; 社本 真一; 本田 孝志*; 池田 一貴*; 大友 季哉*; 畑 博人*; 江藤 貴弘*; 野田 正亮*; et al.

Scientific Reports (Internet), 8(1), p.9651_1 - 9651_8, 2018/06

 被引用回数:2 パーセンタイル:41.94(Multidisciplinary Sciences)

The electron-doped SrTiO$$_{3}$$ exhibits good thermoelectric properties, which makes this material a promising candidate of an n-type oxide thermoelectric device. Recent studies indicated that only a few percent co-doping of La and Mn in SrTiO$$_{3}$$ substantially reduces the thermal conductivity, thereby greatly improving the thermoelectric figure of merit at room temperature. Our time-of-flight neutron scattering studies revealed that by doping both La and Mn into SrTiO$$_{3}$$, the inelastic scattering spectrum shows a momentum-independent increase in the low-energy spectral weight approximately below 10 meV. The increase in the low-energy spectral weight exhibits a clear correlation with thermal conductivity. The correlation is attributed to dynamical and local structural fluctuations caused by the Jahn-Teller instability in Mn$$^{3+}$$ ions coupled with the incipient ferroelectric nature of SrTiO$$_{3}$$, as the origin of the low thermal conductivity.

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