0.7-x
x
0.3
3
*
School of Physics, University of Hyderabad, Central University P.O., Hyderabad 500046, India
* Corresponding author`s email : rssp@uohyd.ernet.in
, Ph: 040-2313 4321, Fax: 040-2301 0227.
The electron spin resonance (ESR) and magnetization
(M) studies were carried out on La
0.7-x
Bi x
Ca
0.3
MnO
3 as a function of temperature
.
The evolution of different magnetic phases with Bi doping are ascribed to difference in ionic radii of La 3+ and Bi 3+ and 6s lone pair of Bi 3+ ion.
Key words: Sol-gel synthesis, Manganites, Electron spin resonance, Magnetization, Phase separation.
The phenomenon of phase separation (PS) and coexistence of magnetic phase at different length scales have been extensively studied in manganites [1, 2]. In the present work we report temperature dependent ESR and magnetization studies of La
0.7-x
Bi x
Ca
0.3
MnO
3 manganite with x = 0, 0.035, 0.35, 0.42, 0.56 and 0.63.
The x- ray diffraction studies show that all the samples are polycrystalline with cubic perovskite structure. Fig.1 (A) shows the peak to peak linewidth
(ΔH) of ESR signal as a function of temperature (T).
ΔH decreases linearly with decreasing temperature from
473 K, reaches to a minimum and this temperature can be assigned as T min
. The linear dependency in ΔH is due to spin lattice relaxation or spin phonon interaction.
Below T min
, ΔH increases with further decrease in temperature. This is due to critical slowing down of the spin fluctuations in the ferromagnetic (FM) phase . T min decrease with increase in Bi doping. Fig.1 (B) shows magnetization (M) as a function of temperature, in zero field cooled (ZFC) and field cooled (FC) modes in an applied field of 500 Oe. M decreases with increase in Bi content except for x = 0.035. The Curie temperature
(T
C
) decreases with increase in Bi content. Two T
C values are indicating two magnetic transitions are observed for all samples. The first one is paramagnetic
(PM) to a weak FM state, and this temperature can be assigned to T
C
with low moment state (T
C
(L)).The second one is PM to robust FM state and this temperature is assigned to T
C
with high moment state
(T
C
(H))[1]. The estimated values of T
C
(L) are close to the values of T min
estimated from ΔH versus (vs) T
Fig.1: ΔH vs T (A) and M vs T (B) for all samples.
ESR spectra of La
0.7
Ca
0.3
MnO
3
(C) plots. For all samples, the temperatures at which peak 1 and 2 are observed in the low field region of ESR spectra (fig. 1C , for x = 0), are strong evidence for T
C
(L) and T
C
(H) respectively. For samples with x ≥ 0.35, strong bifurcation between ZFC and FC curves is observed below ~ 40 K similar to the Bi
1-x
Ca x
MnO
3 system [2]. These features are attributed to simultaneous evolution of FM and charge ordered (CO) antiferromagnetic (AFM) phases [1, 2].
The decrease in
M, T
C
and evolving different magnetic phases with Bi doping are ascribed to the difference of ionic radii of
La 3+ and Bi 3+ and 6s lone pair of Bi 3+ ion.
Ramesh Ade is grateful for the award of UGC-
SRF from CSIR India.
[1] J. R. Sun, J. Gao, Y. Fei, R. W. Li, and B. G. Shen,
“Doping effects on the phase separation in perovskite La
0.67x
Bi x
Ca
0.33
MnO
3
”, Phys. Rev. B 67,
(2003), pp. 144414(1)- 144414(10).
[2] A. Ramesh and R. Singh, “Electron spin resonance and magnetization studies of Bi
1x
Ca x
MnO
3
”,
Physica B (2014) in press.