Electron-Spin Resonance of a La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ Slab

We have studied electron-spin resonance (ESR) spectra of a La
_0.7
Sr
_0.3
MnO
₃
slab. Experimental results reveal that ESR spectra in the ferromagnetic (FM) region are followed with a broadly resonant mode as θ = 90
^°
, but several modes as θ = 0
^°
. Their spectral parameters depend strongly on θ. When keeping θ = 0
^°
and measuring the temperature dependence of ESR spectra, it is found that several resonant modes in the FM region become a single mode in the Dysonian line-shape at temperatures
T
>;
T
_min
≈ 1.1
TC
. At
T
_min
, the spectral linewidth reaches to a minimum value of Δ
H
_min
= 283 Oe. Temperature dependences of the EPR intensity above
T
_min
obey a function
I
(
T
) =
Io
exp(
Ea
/
kB T
). Having based on the relation of
I
(
T
) ∝ χ(
T
) = 1/(
T
-Θ) , we obtained the Curie-Weiss temperature Θ to be 376 K. If using a simple relation of
g
=
h
ν/ μ
B Hr
(
Hr
is the resonant position, and μ
B
is the Bohr magneton), we have found that the effective Lande factor
g
increases from 1.91 (around
T
_min
) to ~ 1.98 (at 473 K) close to the value of
g
= 2.0 for spin-spin interactions of Mn ions. This could be due to the additional presence of magnetic interactions, besides spin-spin interactions, such as interactions between FM clusters and/or spin-orbital coupling. Interestingly, despite the sample in the PM regime, the spectral parameters depend on the angle θ. This is assigned to an anisotropic field related to Mn
³⁺
-Mn
^{4 +}
FM clusters persisting above
T
_min
. At 470 K, the anisotropy constant obtained is
Ku
≈ 57 erg/cm
³
, much smaller than that in the FM region.