Journal of Superconductivity and Novel Magnetism
https://doi.org/10.1007/s10948-018-4902-6
ORIGINAL PAPER
Magnetic Properties and M ¨ ossbauer Investigations
of La
0.67
Sr
0.33
Fe
x
Mn
1-x
O
3
(x = 0 and 0.5) Perovskites
Itegbeyogene P. Ezekiel
1
· Thomas Moyo
1
Received: 2 July 2018 / Accepted: 26 September 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
We report magnetic phase separation in pure La
0.67
Sr
0.33
Fe
x
Mn
1−x
O
3
(x = 0 and 0.5) ceramic samples. Rhombohedral
crystal structures obtained with R3C space group show no significant changes in the lattice structures due to the close values
of ionic radii of Fe
3+
and Mn
3+
ions. However, significant changes occur in the magnetic properties due to competing
ferromagnetic (FM) and antiferromagnetic (AFM) interactions because of the presence of Fe
3+
substitution. The FM double
exchange interactions (DE) (Mn
3+
–O–Mn
4+
) appears suppressed by AFM superexchange interactions (Fe
3+
–O–Mn
4+
,
Fe
3+
–O–Fe
3+
, Mn
4+
–O–Mn
4+
). The saturation magnetization for x = 0 has the highest value of approximately 80 emu/g
at 2 K, which dropped significantly to approximately 5 emu/g at 2 K for the x = 0.5 sample. The coercivity (H
c
) for x = 0.5
increased from 161 Oe at 300 K to 786 Oe at 2 K compared with that of x = 0 which varied from 110 to 150 Oe. A value
of H
c
(0) = 1.5 ± 0.04 kOe was extrapolated from the model fit to the temperature dependence of H
c
. The temperature-
dependent
57
Fe M¨ ossbauer spectroscopy measurements show the presence of Fe in two different environments that have
an AFM Fe
3+
–O–Mn
4+
and Fe
3+/2+
–O–Fe
3+/2+
coordination. The unequal fraction population of Fe ions at both AFM
environments seems to increase the exchange bias effect.
Keywords Ferromagnetism · Antiferromagnetism · Exchange bias field · Coercivity · Magnetization
1 Introduction
The numerous applications and the fundamental under-
standing of the structure and magnetic properties of hole-
and electron-doped lanthanum-based perovskite mangan-
ite, have informed research efforts towards these materials
[1–7]. The basic structure is LaMnO
3
known to be anti-
ferromagnetic [8], and several possible substitutions into
this structure can occur. Substituted or doped compounds
of interest have the form, La
1−x
A
x
B
y
Mn
1−y
O
3
, where on
the tetrahedral (A) site is one or more of the alkaline earth
elements such as Ca, Sr, and Ba, and on the octahedral (B)
site is one or more of the transition elements such as Fe,
Co, Ni, and Cu [3, 7–13]. Moreover, A- and B-site dop-
ing are known as a hole and electron doping, respectively
Itegbeyogene P. Ezekiel
itegbeyogene@gmail.com
1
School of Chemistry and Physics, Westville Campus,
University of KwaZulu-Natal, Private Bag X54001,
Durban, South Africa
[9, 10]. Depending on the dopants and concentration, a
ratio of Mn
3+
and Mn
4+
ions exist in the octahedral crys-
tal structure (MnO
6
) at the B site which interact through
a ferromagnetic (FM) double-exchange (DE) interaction
[11]. Interesting properties depend on this DE interaction.
However, there are reports which show that some physical
properties derived from these materials do not only depend
on the DE interactions. Several factors such as oxygen
deficiency, phase separation, and the Jahn-Teller distortion,
which arise from the strong electron-phonon coupling, can
also play a significant role [8, 12–17]. For example, oxygen
excess will create more Mn
4+
ions that lead to additional
antiferromagnetic (AFM) interactions of Mn
4+
–O–Mn
4+
ions [18]. The sum of these interactions creates complex
magnetic phases of coexisting and competing ferromagnetic
and antiferromagnetic or paramagnetic phases [18].
Ferromagnetic interactions are strongest when the
ratio of Mn
3+
:Mn
4+
ions is about 7:3, which corre-
sponds to La
0.7
Sr
0.3
MnO
3
composition [8]. However, the
La
0.67
Sr
0.33
MnO
3
composition reported to be optimum has
attracted the most attention because it has a large mag-
netic moment and a Curie temperature of about 370 K