  We present the first results from the "Low Energy Detector" payload of the
"Solar X-ray Spectrometer (SOXS)" mission, which was launched onboard the
GSAT-2 Indian spacecraft on 08 May 2003 by the GSLV-D2 rocket to study solar
flares. The SOXS Low Energy Detector (SLD) payload was designed, developed, and
fabricated by the Physical Research Laboratory (PRL) in collaboration with the
Space Application Centre (SAC), Ahmedabad and the ISRO Satellite Centre (ISAC),
Bangalore of Indian Space Research Organization (ISRO). The energy ranges of
the Si PIN and CZT detectors are 4 - 25 keV and 4 - 56 keV respectively. The Si
PIN provides sub-keV energy resolution while the CZT reveals ~1.7 keV energy
resolution throughout the energy range. The high sensitivity and sub-keV energy
resolution of the Si PIN detector allows measuring the intensity, peak energy,
and the equivalent width of the Fe-line complex at approximately 6.7 keV as a
function of time in all ten M-class flares studied in this investigation. The
peak energy (Ep) of the Fe-line feature varies between 6.4 and 6.7 keV with
increasing in temperature from 9 to 58 MK. We found that the equivalent width
(w) of the Fe-line feature increases exponentially with temperature up to 30 MK
and then increases very slowly up to 40 Mk. It remains between 3.5 and 4 keV in
the temperature range of 30 - 45 MK. We compare our measurements of w with
calculations made earlier by various investigators and propose that these
measurements may improve theoretical models. We interpret the variation of both
Ep and w with temperature as due to the changes in the ionization and
recombination conditions in the plasma during the flare interval and as a
consequence the contribution from different ionic emission lines also varies.
