Magnetism of gadolinium nanoparticles near $T_{c}$

Influence of temperature and magnetic field $H$ on magnetism of spherical Gd nanoparticles of different sizes (89, 63, 47, 28, and 18 nm) was studied in the temperature range 250 $K<T<$ 325 K. The particles were obtained by metal vapor condensation in the flow of helium. The particles with $d$ = 18 nm did not show a magnetic transition; their structure is a combination of two cubic phases (FCC1 and FCC2). Large particles remained in the HCP phase and had an admixture of the FCC1 phase, the amount of which decreased as the particle sizes increased; magnetic transition took place at $T_{c}$ = 293 K. The admixture of O$_2$ did not alter the structure but decreased the magnetization $\sigma$ and magnetic permeability $\mu$. An orientation transition in polycrystalline gadolinium initiated by the magnetic field H was proved in an experiment. The orientation transition in Gd particles smaller than 63 nm, the magnetic structure of which is close to the single-domain structure, occurred near $T_{c}$ without the influence of $H$.