Magnetic resonance in gadolinium nanoparticles near the curie point

The Influence of temperature in the range from 275 to 320 K on ESR spectra and magnetization m of ensembles of spherical gadolinium nanoparticles with the diameter from 89 to 18 nm was studied. The particles with $d$ = 18 nm had a cubic face centered structure and no magnetic transition. At $T>T_C$ all particles were paramagnetic, and their $g$ factors were $g$ = 1.98 $\pm$ 0.02 irrespective of their size and structure. At $T=T_C$ the particles having 28 to 89 nm in size experienced a magnetic and orientation transition; at $T<T_C$ their $m(H)$ dependences were described by the Langevin function, and the FMR lines broadened and shifted towards $H$ = 0. FMR lines of the Gd particle ensembles showed a hysteresis behavior during magnetization reversal, which did not correlate with the coercivity of the particles. Dependences of the Gd nanoparticles FMR linewidth $\Delta H(T)$ changed proportionally to $|T-T_C|$.