Lattice effects of orbital and charge orderings in the perovskite manganite Pr 1 − x Ca x MnO 3
Lattice effects of orbital and charge orderings in the perovskite manganite Pr 1 − x Ca x MnO 3
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DOI：
10.1103/physrevb.69.064406
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发表时间：
2004-02
影响因子：
3.7
通讯作者：
H. Hazama;T. Goto;Y. Nemoto;Y. Tomioka;A. Asamitsu;Y. Tokura
中科院分区：
文献类型：
--
作者：
H. Hazama;T. Goto;Y. Nemoto;Y. Tomioka;A. Asamitsu;Y. Tokura
We have made ultrasonic measurements of ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ $(x=0.35,$0.40,0.50) with the colossal magnetoresistance in order to investigate the lattice effects due to orbital and charge degrees of freedom in the systems. As a result, we observe three types of elastic softening. The first one is the softening of ${(C}_{11}\ensuremath{-}{C}_{12})/2$ in the $x=0.35,$ 0.40, and 0.50 compounds above the charge-ordering point ${T}_{\mathrm{co}},$ which originates from the interaction of the quadrupoles ${O}_{2}^{0}$ and ${O}_{2}^{2}$ with ${\ensuremath{\Gamma}}_{3}$ symmetry of ${e}_{g}$ orbital in ${\mathrm{Mn}}^{3+}$ ions to elastic strains. The second one is the softening of ${C}_{44}$ in the $x=0.50$ just above ${T}_{\mathrm{co}},$ which is caused by a coupling of the charge-fluctuation mode with ${\ensuremath{\Gamma}}_{5}$ symmetry in the coexistence ratio $N({\mathrm{Mn}}^{3+}):$$N({\mathrm{Mn}}^{4+})=1:1$ to the appropriate elastic strain. Employing a group-theoretical analysis based on the Landau theory for the phase transition, we have successfully deduced the ${Q}_{\mathrm{xy}}$-type charge-fluctuation mode with ${\ensuremath{\Gamma}}_{5}$ symmetry for the order parameter below ${T}_{\mathrm{co}},$ there being alternative alignment on Mn${}^{3+}$ and Mn${}^{4+}$ ions in $a\ensuremath{-}c$ $(x\ensuremath{-}y)$ plane and the same arrangement along $b(z)$ direction. The last one is the softening of ${(C}_{11}\ensuremath{-}{C}_{12})/2$ just above ${T}_{\mathrm{co}}$ due to the charge fluctuation.
We have made ultrasonic measurements of ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ $(x=0.35,$0.40,0.50) with the colossal magnetoresistance in order to investigate the lattice effects due to orbital and charge degrees of freedom in the systems. As a result, we observe three types of elastic softening. The first one is the softening of ${(C}_{11}\ensuremath{-}{C}_{12})/2$ in the $x=0.35,$ 0.40, and 0.50 compounds above the charge-ordering point ${T}_{\mathrm{co}},$ which originates from the interaction of the quadrupoles ${O}_{2}^{0}$ and ${O}_{2}^{2}$ with ${\ensuremath{\Gamma}}_{3}$ symmetry of ${e}_{g}$ orbital in ${\mathrm{Mn}}^{3+}$ ions to elastic strains. The second one is the softening of ${C}_{44}$ in the $x=0.50$ just above ${T}_{\mathrm{co}},$ which is caused by a coupling of the charge-fluctuation mode with ${\ensuremath{\Gamma}}_{5}$ symmetry in the coexistence ratio $N({\mathrm{Mn}}^{3+}):$$N({\mathrm{Mn}}^{4+})=1:1$ to the appropriate elastic strain. Employing a group-theoretical analysis based on the Landau theory for the phase transition, we have successfully deduced the ${Q}_{\mathrm{xy}}$-type charge-fluctuation mode with ${\ensuremath{\Gamma}}_{5}$ symmetry for the order parameter below ${T}_{\mathrm{co}},$ there being alternative alignment on Mn${}^{3+}$ and Mn${}^{4+}$ ions in $a\ensuremath{-}c$ $(x\ensuremath{-}y)$ plane and the same arrangement along $b(z)$ direction. The last one is the softening of ${(C}_{11}\ensuremath{-}{C}_{12})/2$ just above ${T}_{\mathrm{co}}$ due to the charge fluctuation.