Regensburg 1998 – wissenschaftliches Programm
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AM: Magnetismus
AM 11: Postersitzung
AM 11.13: Poster
Dienstag, 24. März 1998, 16:15–20:00, B
Magnetization and magnetic phases in metallic and semiconducting HoxCa1−xMnO3 — •H. Schmid, T. Zeiske, K. Knorr, and W. Prandl — Institut f"ur Kristallographie Universit"at T"ubingen, Charlottenstra"se 33, 72070 T"ubingen
We have measured the magnetization, suszeptibility, specific resistance,
X-Ray and neutron diffraction data of the series (HoxCa1−x)MnO3
(x ≤ 0.5; step width Δx = 0.1 or less). The compounds analyzed
have distorted perovskite structures: they are orthorhombic for
0 ≤ x ≤ 0.13, and have an orthorhombic to monoclinic phase
transition
for 0.13 ≤ x ≤ 0.33 with TOM =TOM(x). Ho ions are
paramagnetic for 4K ≤ T ≤ 300K. Their magnetization and
susceptibility at low temperatures are, however, reduced from what one
expects free ions. We calculate a crystal field correction
MHo(T,H) and χHo(T). The resulting data for Mn shows a
ferromagnetic
phase at x=0.1 ± 0.05 and ordering temperatures
TN/Tc ≈110K.
These results show that (HoxCa1−x)MnO3 belongs to the family
of giant
magnetoresistance compounds (LaxCa1−x)MnO3 with, however, the
ferromagnetic phase occuring at x=0.1 as compared to x=0.67
in the La-compound.
>From this observation we draw the conclusion that the concentration
Mnx3+Mn1−x4+ is of minor importance for the occurrence of
ferromagnetism: it is evidently the size of RE ion
(rHo=0.89 23 A; rLa=1.39 23 A)
which is essential.
We acknowledge the support by the Deutsche Forschungsgemeinschaft
(Proj. PR44/8-1).