A preliminary investigation of large shift in transition temperature (Tc) in Gd₅Si₃ nanoparticles

Magnetic ordering temperatures in nanostructures depend on size. Curie temperature(Tc) of a bulk material where exchange interactions are comparable to thermal fluctuations tends to decrease in particles. The decrease of ordering temperature with size is described by the scaling theory of Fisher & Barber.
However, a large increase in Tc in Gd₅Si₃ NPs have been observed in the ball-milled gadolinium silicide. SEM images shows particle sizes ranging from 50 nm to >2 μm. XRD analysis on pre-separated sample show that ferromagnetic Gd₅Si₄ is the major phase while paramagnetic Gd₅Si₃ is the minor phase. Magnetic properties measured in VSM reveal that the Tc decreases for Gd₅Si₄ phase from 332K for bulk to 315K for ball-milled sample. Another Tc observed at 80K is attributed to Gd₅Si₃ phase undergoes large shift in its transition temperature at 110K and remains constant irrespective of particle sizes.
Plausible reasons for the increase in Tc for Gd₅Si₃ NPs could be due to the effect of high energy mechanical ball-milling process that could induce structural changes, lattice strains, exchange interaction between phases in a particle, or formation of new phase.