Nanoscience and Nano Technology

Biography

Biography: Bhaskar Das

Abstract

Mn-based silicides are attractive from the viewpoints of fundamental science and potential applications in spintronics, owing to their exotic spin textures and unique crystal structures. However, bulk alloys show only weak low-temperature magnetic ordering and this inhibits their practical room-temperature applications. Our recent report shows that magnetic nanoclusters exhibit entirely different magnetic properties from the corresponding bulk alloys due to nanoscale effects. In this study, we report the synthesis of novel Mn₅Si₃ nanoclusters using a gas-aggregation type cluster-deposition method and show unusual ferromagnetism experimentally and by first-principle DFT calculations, in a sharp contrast to antiferromagnetic behavior shown by bulk alloys below 100 K. TEM studies show that Mn₅Si₃ nanoclusters are monodispersed with an average size d » 8.7 nm and an rms standard deviation σ/d»0.1. The nanoclusters are also single crystalline and form the D8₈-type hexagonal structure as shown by HRTEM (Figure-1a) and FFT (Figure-1b) images, respectively. The nanoclusters show appreciable coercivities (H_c=900 Oe at 3 K and 450 Oe at 300 K) and high saturation magnetic polarization (J_s=12.5 kG at 3 K and 10.5 kG at 300 K) [Figure-1(c)] with a high Curie temperature (T_c≈590 K) [Figure-1(d)]. The fitting of magnetization curve at high-field region (35-70 kOe) using the law-of-approach to saturation method yields an appreciable magneto crystalline anisotropy constant K₁≈12 Mergs/cm³. Thus, easy-axes of the nanoclusters were successfully aligned using an external magnetic field prior to deposition, which results in improved H_c (1700 Oe at 3 K and 600 Oe at 300 K). The nanocluster magnetic properties are mainly due to the large surface spin-polarization (m=3.3 µ_B/Mn) that subsequently spin-polarizes the nanocluster-core (m=0.9 µ_B/Mn), as revealed by the DFT simulations.