Canted antiferromagnetism and magnetoelastic coupling in metallic Ho<Subscript>0.1</Subscript>Ca<Subscript>0.9</Subscript>MnO<Subscript>3</Subscript>

Ho<Subscript>0.1</Subscript>Ca<Subscript>0.9</Subscript>MnO<Subscript>3</S ubscript> is a canted antiferromagnet with the magnetic space group Pn′ma′. The magnetic structure is a superposition C<Subscript> x </Subscript>F<Subscript> y </Subscript>A<Subscript> z </Subscript> of the three types of order allowed in Pn′ma′. In the Ca-rich corner of the system Ho<Subscript>1−x </Subscript>Ca<Subscript> x </Subscript>MnO<Subscript>3</Subscript> the title compound has a strong magnetoelastic distortion ΔV <Subscript>MAG</Subscript>/V=1.2 × 10<Superscript>−3</Superscript>, the highest metallic conductivity and a ferromagnetic component F<Subscript> y </Subscript> 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 <Subscript>N</Subscript>=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 <Subscript>N</Subscript>. MnO<Subscript>6</Subscript> 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 <Subscript>N</Subscript> we find small polaron conductivity. The presence of the Jahn-Teller distortion due to the only small abundance (10%) of Mn<Superscript>3+</Superscript> in the t<Stack> <Subscript>2g</Subscript> <Superscript>3</Superscript> </Stack>e<Subscript>g</Subscript> configuration is attributed to delocalised e<Subscript>g</Subscript> electrons. In the magnetically ordered state the averaged magnetic moment of Mn is reduced appreciably from the paramagnetic value due to spin disorder. Copyright Società Italiana di Fisica, Springer-Verlag 1999