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$$R$$-dependence of spin exchange interactions in $$R$$MnO$$_{3}$$ ($$R$$ = Rare-Earth Ions)

$$R$$MnO$$_{3}$$($$R$$=希土類イオン)におけるスピン交換相互作用の$$R$$依存性

梶本 亮一 ; 望月 秀記*; 吉澤 英樹*; 新谷 寛*; 木村 剛*; 十倉 好紀*

Kajimoto, Ryoichi; Mochizuki, Hidenori*; Yoshizawa, Hideki*; Shintani, Hiroshi*; Kimura, Tsuyoshi*; Tokura, Yoshinori*

A型反強磁性秩序を示すPrMnO$$_{3}$$と長距離磁気秩序を示すTbMnO$$_{3}$$のマグノン励起を中性子非弾性散乱実験によって調べた。LaMnO$$_{3}$$の結果(K. Hirota $textit{et al.}$)も合わせて議論することで$$R$$イオンの違いによるスピン交換相互作用の系統的な変化を明らかにした。$$R$$イオンの半径が小さくなるにつれて$$ab$$面内の最近接サイト間の交換相互作用は急激に減少し、TbMnO$$_{3}$$では有限の次近接サイト間交換相互作用が存在する。対照的に$$c$$軸方向の交換相互作用の$$R$$依存性は非常に小さい。これらの結果は、$$R$$MnO$$_{3}$$における磁気構造の変化は最近接サイト間相互作用と次近接サイト間相互作用の競合によって引き起こされるという説(T. Kimura $textit{et al.}$)と整合している。

Magnon excitations have been investigated for PrMnO$$_{3}$$ showing the $textit{A}$-type antiferromagnetic ordering and TbMnO$$_{3}$$ forming a long-period spin ordering by inelastic neutron scattering. Combined with a result of LaMnO$$_{3}$$ [K.~Hirota $textit{et al.}$], the systematic data revealed that the ferromagnetic exchange interaction between nearest-neighbor (NN) Mn sites within the $$ab$$ plane drastically decreases in $$R$$MnO$$_{3}$$ as the ionic radius of $$R$$ is reduced. In addition, finite next-nearest-neighbor (NNN) coupling is evident in TbMnO$$_{3}$$. In contrast, the exchange interaction along the $$c$$ axis shows much weaker $$R$$ dependence consistent with the Mn-O-Mn bond angle. These observations confirm a scenario that explains the evolution of spin structures in $$R$$MnO$$_{3}$$ in terms of the competition between the NN and NNN interactions [T.Kimura $textit{et al.}$].

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パーセンタイル:19.84

分野:Physics, Multidisciplinary

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