Canted antiferromagnetism and magnetoelastic coupling in metallic Ho0.1Ca0.9MnO3

Ho0.1Ca0.9MnO3 is a canted antiferromagnet with the magnetic space group Pn ' ma '. The magnetic structure is a superposition C x F y A z of the three types of order allowed in Pn ' ma '. In the Ca-rich corner of the system Ho _1-x Ca x MnO ₃ the title compound has a strong magnetoelastic distortion , the highest metallic conductivity and a ferromagnetic component F y close to the maximum in the series. Among the areas ab, bc, ca calculated from the lattice constants only ca shows a strong magnetoelastic effect below T N = 106 K. The x-, y-, z-spin components depend differently on the temperature. This gives rise to spin rotation which is particularly strong close to T N. MnO ₆ octahedra have short bond lengths with a temperature independent average . They are practically regular at room temperature and show a Jahn-Teller distortion of 3.5% in the magnetically ordered state. Above T N we find small polaron conductivity. The presence of the Jahn-Teller distortion due to the only small abundance (10%) of Mn ³⁺ in the t _2g ³ e g configuration is attributed to delocalised e g electrons. In the magnetically ordered state the averaged magnetic moment of Mn is reduced appreciably from the paramagnetic value due to spin disorder. Received 21 January 1999