Control of electronic properties by lanthanide size and manganese oxidation state in the MnIII/MnIV Ruddlesden–Popper phases Ln2-xSr1+xMn2O7
Abstract
The magnetic behaviour of then=2 Ruddlesden–Popper
phases Sr
2
LnMn
2
O
7
is very sensitive to
the Ln
3+
lanthanide cation. In samples with larger, more basic
lanthanide cations (Ln=Nd, Pr) antiferromagnetic phases with ordering
temperatures in the region of 130 K co-exist with phases showing a
magnetic response suggestive of superparamagnetism or the development of
small ferromagnetic clusters at high temperature. The magnetic transition
temperature drops to 20 K in samples containing smaller, acidic cations
(Ln=Gd–Er, Y). In the latter group of compounds, the transition is
from a Curie–Weiss paramagnet to a spin-glass; there is no evidence
for long-range magnetic order. This change in behaviour can be explained
by considering the variation in the relative strength of superexchange and
double exchange interactions as a function of the lanthanide cation. The
influence of manganese oxidation state on magnetic response is
investigated in the Sr
2-x
Ln
1+x
Mn
2
O
7
composition range
(0.0≤x≤0.7) for Ln=Nd, Tb.
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