ARTICLE IN PRESS

Journal of Magnetism and Magnetic Materials 272–276 (2004) 405–406

Dramatic change of magnetic property in the A-site ordered/disordered manganites PrBaMn2O6 /Pr0:5Ba0:5MnO3
T. Nakajima*, H. Kageyama, Y. Ueda
Materials Design and Characterization Laboratory, Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8581, Japan

Abstract
The magnetic properties of the A-site ordered/disordered manganese perovskite PrBaMn2 O6 /Pr0:5 Ba0:5 MnO3 havebeen investigated in terms of the extent of the A-site randomness. The A-site disorder suppresses both ferromagnetic
and A-type antiferromagnetic transitions in the A-site ordered PrBaMn2 O6 ; and leads to a magnetic glassy state in thestrong disordered Pr0:5 Ba0:5 MnO3 : Ultrasharp and stepwise changes of magnetization and resistivity have been
observed in the strong disordered Pr0:5 Ba0:5 MnO3 :r 2003 Elsevier B.V. All rights reserved.
Keywords: New metal-ordered/disordered manganites; RBaMn2 O6Due to the rich physical properties including thecolossal magnetoresistance (CMR), manganese perovskites have drawn much attention in the ﬁelds of physics
and engineering [1]. Many experimental and theoreticalstudies have revealed that the interesting properties suchas CMR and electronic phase separation come from a
critical competition between a ferromagnetic metal andan antiferromagnetic charge–orbital order interaction,
which could be signiﬁcantly inﬂuenced by the A-site
randomness or a ﬂuctuation of composition [2,3].
Recently, we synthesized the A-site ordered manganeseperovskites RBaMn2 O6 (R=Y and rare earth elements)
and reported the electronic phase diagram of
RBaMn2 O6 [4]. The novel properties observed in
RBaMn2 O6 are not only due to the absence of the Asite randomness but also due to the layer-type structurewith the BaO–MnO2 –RO–MnO2 stacking sequence
along the c-axis [4–6]. We also successfully synthesized
the A-site disordered R0:5 Ba0:5 MnO3 and have studied
the A-site randomness effect in Ba-based manganites. In
this paper, we report the magnetic properties of theordered/disordered PrBaMn2 O6 /Pr0:5 Ba0:5 MnO3 ; whichstrongly depend on the extent of randomness with Pr
and Ba in the A-site.
*Corresponding author. Tel./fax: +81-471-36-3436.
E-mail address: t-nakaji@issp.u-tokyo.ac.jp (T. Nakajima).

Powder samples of the ordered PrBaMn2 O6 weresynthesized by a solid-state reaction of Pr6 O11 ; BaCO3
and MnO2 as described in Ref. [4]. The extent of the Asite disorder strongly depended on the preparation
process. The weak disordered samples were obtainedby annealing the ordered samples at 90021300 C in O2gas. The strong disordered samples were prepared by asolid- state reaction of the same starting materials in at1350 C 1% O2 /Ar gas, followed by annealing at 900 C
in O2 gas. The obtained products were checked to be
single phase by X-ray diffraction using CuKa radiation.
The extent of order/disorder with Pr and Ba wasestimated by the peak intensity of (0 0 12)p reﬂection
indexed with the primitive cell.
The ordered PrBaMn2 O6 with the strong (0 0 12)p(reﬂection has a tetragonal structure (a=3.9088(1) A,(
c=7.7649(4) A),
whilethestrong
disordered
Pr0:5 Ba0:5 MnO3 without (0 0 12)p reﬂection has a cubic(structure (a=3.8951(1) A).
The weak disordered
Pr0:5 Ba0:5 MnO3 ; which shows the weak (0012)p(reﬂection has a tetragonal structure (a=3.9038(2) A,(
c=7.7906(7) A).
The magnetic susceptibilities (M=H) measured under1000 Oe are shown in Fig. 1. The ordered PrBaMn2 O6shows the ferromagnetic transition at TC =310 K,
followed by the A-type antiferromagnetic transition at
TN =270 K (Fig. 1(a)). The weak disordered0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2003.12.341

ARTICLE IN PRESS
406

T. Nakajima et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 405–406

magnetic ordering, namely that could occur as a resultof the competition between randomly distributed
ferromagnetic and antiferromagnetic interactions. Since
the ionic radius of Ba2þ is much larger than Sr2þ( [7], the strong disordered R0:5 Ba0:5 MnO3 may(=1.44 A)
include the special heterogeneity in nanometer size,
which leads to the magnetic nonhomogeneous state.
Very interestingly, ultrasharp and stepwise changes ofmagnetization and resistivity have been observed in thestrong disordered Pr0:5 Ba0:5 MnO3 [8]. The microscopic
measurements such as neutron diffraction and electron
microscopy are now in progress in order to fully
understand these behaviors.

Fig. 1. The magnetic susceptibilities (M=H) of (a) ordered(&:ZFC), (b) weak disordered (W:ZFC) and (c) strong
disordered (J:ZFC, K:FC) PrBaMn2 O6 as a function oftemperature.

Pr0:5 Ba0:5 MnO3 exhibits the ferromagnetic transition atTC =160 K (Fig. 1(b)) but does no transition below
160 K. The strong disordered Pr0:5 Ba0:5 MnO3 has amagnetic transition at 160 K, showing a very small
spontaneous magnetic moment about 0.2 mB and asigniﬁcant difference of M=H–T curves on zero-ﬁeldcooled (ZFC) and ﬁeld cooled (FC) processes. The Asite randomness clearly suppresses not only the ferromagnetic transition but also the A-type antiferromagnetic transition to much extent. It is natural that the Asite disorder destabilizes the A-type antiferromagnetic
state associated with the dx2 y2 orbital order (layer type).
On the other hand, the magnetic glassy behavior
observed in the strong disordered Pr0:5 Ba0:5 MnO3 could
be due to a disorder effect that hinders the long-range

The authors thank T. Yamauchi, M. Isobe, Z. Hiroi
and H. Fukuyama for fruitful discussion. This work is
partly supported by Grants-in-Aid for Scientiﬁc Research (No. 407 and 758) and for Creative ScientiﬁcResearch (No. 13NP0201) from the Ministry of Education, Culture, Sports, Science, and Technology.

References[1] C.N.R. Rao, B. Raveau, Colossal Magnetoresistance,
Charge Ordering and Related Properties of Manganese
Oxides, World Scientiﬁc, Singapore, 1998.
[2] H. Aliaga, et al., cond-mat/0303513.
[3] F. Millange, V. Caignaert, B. Domeng"es, B. Raveau, Chem.
Mater. 10 (1998) 1974.
[4] T. Nakajima, H. Kageyama, H. Yoshizawa, Y. Ueda,J. Phys. Soc. Japan 71 (2002) 2843.
[5] T. Nakajima, H. Kageyama, Y. Ueda, J. Phys. Chem. Solids
63 (2002) 913.
[6] H. Kageyama, T. Nakajima, H. Yoshizawa, M. Ichihara, K.
Ohoyama, Y. Ueda, J. Phys. Soc. Japan 72 (2003) 241.
[7] R. D. Shannon, Acta Crystallogr, A 32 (1976) 751.
[8] T. Nakajima, et al., J. Alloys Compd. (in press).