  This paper presents an investigation of spectral properties of 10 millisecond
pulsars (MSPs) discovered by the uGMRT, observed from 2017-2023 using band 3
(300-500 MHz) and 4 (550-750 MHz) of uGMRT. For these MSPs, we have reported a
range of spectral indices from ~0 to -4.8, while averaging the full observing
band and all the observing epochs. For every MSP, we calculated the mean flux
densities across 7-8 sub-bands each with approximately 25 MHz bandwidth
spanning band 3 and band 4. We computed their modulation indices as well as
average and maximum-to-median flux densities within each subband. Using a
temporal variation of flux density we calculated the refractive scintillation
time scales and estimated structure function with time lag for 8 MSPs in the
sample. We note a significant temporal evolution of the in-band spectra,
classified into three categories based on the nature of the best-fit power-law
spectra, having single positive spectral indices, multiple broken power law,
and single negative spectral indices. Additionally, indications of
low-frequency turnover and a temporal variation of the turnover frequency (to
the extent that turnover was observed for some of the epochs while not seen for
the rest) were noted for all the MSPs. To the best of our knowledge, this is
the first systematic investigation probing temporal changes in the MSP spectra
as well as in turnover frequency. Future exploration with dense monitoring
combined with modeling of spectra can provide vital insight into the intrinsic
emission properties of the MSPs and ISM properties.
