Canted Antiferromagnetism and Magnetoelastic Coupling in Metallic Ho 0.1 Ca 0.9 MnO 3

Ho 0.1 Ca 0.9 MnO 3 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 ΔV MAG / V = 1.2 × 10 −3 , 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 〈MnO〉 = 1.91 Å. 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.