  Lithium ferrites are well known materials due to their numerous technological
applications especially in microwave devices. Mn-doped lithium ferrite
nanoparticles were prepared by sol-gel technique by means of Pechini method,
and then annealed at different temperatures in 250 to 1000 {\deg}C range. XRD
confirms spinel formation with particle size in the 15 to 200 nm range, with
increased size with annealing temperature. Microwave magnetoabsorption data of
annealed lithium ferrite nanoparticles, obtained with a broadband system based
on a network analyzer operating up to 8.5 GHz are presented. At fields up to
200 mT we can observe a broad absorption peak that shifts to higher frequencies
with magnetic field according to ferromagnetic resonance theory. The amplitude
of absorption, up to 85%, together with the frequency width of about 4.5 GHz
makes this material suitable as wave absorber. Samples annealed at higher
temperatures show a behaviour similar to polycrystalline samples, thus
suggesting their multidomain character
