Control of Magnetic Ordering by Jahn-Teller Distortions in Nd2GaMnO6 and La2GaMnO6
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- 作者：Edmund J. Cussen ; Matthew J. Rosseinsky ; Peter D. Battle ; Jonathan C. Burley ; Lauren E. Spring ; Jaap F. Vente ; Stephen J. Blundell ; Amalia I. Coldea ; and John Singleton
- 刊名：Journal of the American Chemical Society
- 出版年：2001
- 出版时间：February 14, 2001
- 年：2001
- 卷：123
- 期：6
- 页码：1111 - 1122
- 全文大小：194K
- 年卷期：v.123,no.6(February 14, 2001)
- ISSN：1520-5126
文摘
The substitution of Ga3+ into the Jahn-Teller distorted, antiferromagnetic perovskites LaMnO3and NdMnO3 strongly affects both the crystal structures and resulting magnetic ordering. In both compoundsthe Ga3+ and Mn3+ cations are disordered over the six coordinate sites. La2GaMnO6 is a ferromagnetic insulator(Tc = 70 K); a moment per Mn cation of 2.08(5) 
B has been determined by neutron powder diffraction at 5K. Bond length and displacement parameter data suggest Jahn-Teller distortions which are both coherent andincoherent with the Pnma space group symmetry of the perovskite structure (a = 5.51122(4) Å, b = 7.80515(6)Å, c = 5.52947(4) Å) at room temperature. The coherent distortion is strongly suppressed in comparison withthe parent LaMnO3 phase, but the displacement ellipsoids suggest that incoherent distortions are significantand arise from local Jahn-Teller distortions. The preparation of the new phase Nd2GaMnO6 has been foundto depend on sample cooling rates, with detailed characterization necessary to ensure phase separation hasbeen avoided. This compound also adopts the GdFeO3-type orthorhombically distorted perovskite structure(space group Pnma, a = 5.64876(1) Å, b = 7.65212(2) Å, c = 5.41943(1) Å at room temperature). However,the B site substitution has a totally different effect on the Jahn-Teller distortion at the Mn3+ centers. Thisphase exhibits a Q2 mode Jahn-Teller distortion similar to that observed in LaMnO3, although reduced inmagnitude as a result of the introduction of Ga3+ onto the B site. There is no evidence of a dynamic Jahn-Teller distortion. At 5 K a ferromagnetically ordered Nd3+ moment of 1.06(6) B is aligned along the y-axisand a moment of 2.8(1) B per Mn3+ is ordered in the xy plane making an angle of 29(2)
deg.gif"> with the y-axis. TheMn3+ moments couple ferromagnetically in the xz plane. However, along the y-axis the moments coupleferromagnetically while the x components are coupled antiferromagnetically. This results in a cantedantiferromagnetic arrangement in which the dominant exchange is ferromagnetic. Nd2GaMnO6 is paramagneticabove 40(5) K, with a paramagnetic moment and Weiss constant of 6.70(2) B and 45.9(4) K, respectively.An ordered moment of 6.08(3) B per Nd2GaMnO6 formula unit was measured by magnetometry at 5 K in anapplied magnetic field of 5 T.
B has been determined by neutron powder diffraction at 5K. Bond length and displacement parameter data suggest Jahn-Teller distortions which are both coherent andincoherent with the Pnma space group symmetry of the perovskite structure (a = 5.51122(4) Å, b = 7.80515(6)Å, c = 5.52947(4) Å) at room temperature. The coherent distortion is strongly suppressed in comparison withthe parent LaMnO3 phase, but the displacement ellipsoids suggest that incoherent distortions are significantand arise from local Jahn-Teller distortions. The preparation of the new phase Nd2GaMnO6 has been foundto depend on sample cooling rates, with detailed characterization necessary to ensure phase separation hasbeen avoided. This compound also adopts the GdFeO3-type orthorhombically distorted perovskite structure(space group Pnma, a = 5.64876(1) Å, b = 7.65212(2) Å, c = 5.41943(1) Å at room temperature). However,the B site substitution has a totally different effect on the Jahn-Teller distortion at the Mn3+ centers. Thisphase exhibits a Q2 mode Jahn-Teller distortion similar to that observed in LaMnO3, although reduced inmagnitude as a result of the introduction of Ga3+ onto the B site. There is no evidence of a dynamic Jahn-Teller distortion. At 5 K a ferromagnetically ordered Nd3+ moment of 1.06(6) B is aligned along the y-axisand a moment of 2.8(1) B per Mn3+ is ordered in the xy plane making an angle of 29(2)deg.gif"> with the y-axis. TheMn3+ moments couple ferromagnetically in the xz plane. However, along the y-axis the moments coupleferromagnetically while the x components are coupled antiferromagnetically. This results in a cantedantiferromagnetic arrangement in which the dominant exchange is ferromagnetic. Nd2GaMnO6 is paramagneticabove 40(5) K, with a paramagnetic moment and Weiss constant of 6.70(2) B and 45.9(4) K, respectively.An ordered moment of 6.08(3) B per Nd2GaMnO6 formula unit was measured by magnetometry at 5 K in anapplied magnetic field of 5 T.