Resonant microwave absorption in Mo-doped LaMnO3 investigated using a vector network analyzer

We investigated the magnetization and magnetic field dependent microwave absorption for multiple frequencies (f = 10 MHz to 7 GHz) at room temperature in LaMn
1-x
Mo
x
O
3
series from x = 0.0 to 0.1. We focus on the parent compound and 6% Mo-doped LaMnO
3
. Mo-substitution transforms the parent compound from the antiferromagnetic insulator to a ferromagnetic conductor by inducing a mixed valence of manganese ions (Mn
²⁺
and Mn
³⁺
) which give rise to the double exchange interaction. The transition temperature was found to increase drastically from T
N
= 140 K (Neel temperature) to T
C
= 240 K for x = 0.06. Microwave transmission measured using a network analyzer shows a dip at a specific field for a frequency f greater than or equal to 2 GHz and it shifts up linearly with frequency, which we suggest to resonance microwave absorption due precessing spins (paramagnetic resonance). The dip shows a maximum amplitude for x = 0.06 in the series, and a minimum amplitude for x = 0.0. The resonance field and linewidth at 6 GHz was found to have no correlation with increasing content of Mo cation.