Magnetization of GaMnN Ceramics Prepared from Nanopowders by an Anaerobic Synthesis and High-Pressure High-Temperature Sintering

摘要

Herein, we report a study on magnetic properties of GaMnN ceramics prepared by no additive high-pressure high-temperature sintering of a range of nanopowders, the latter made via an anaerobic synthesis method in the Ga/Mn bimetallic system at various nitridation temperatures and different levels of initial Mn concentration. Measurements of the magnetization as a function of temperature and magnetic field for the ceramics and parent nanopowders showed a typical paramagnetic behavior. Antiferromagnetic interactions between Mn-ions incorporated in the GaN lattice, GaMnN, were revealed and shown to be much stronger in the ceramics than in the respective nanopowders. In addition, in all of these materials an antiferromagnetic contribution originating from a residual Mn2SiO4 by-product was also observed. The highest calculated Mn concentration in the nanopowders reached 3.4 at.%. Complex mixtures of gallium nitride polytypes with multimodal particle size distributions in the nanosized range (small nano: 2-8 nm, large nano: 35-60 nm) were converted upon sintering to the single hexagonal GaN phase with average crystallite sizes of 40-80 nm and higher. For the optimal 700 degrees C-treated materials, the Mn concentration in the parent GaMnN nanopowder was 3.2 at.% whereas in the derived ceramics it amounted to 5.5 at.%. At the same time, contributions of the adventitious Mn2SiO4 by-product significantly decreased upon sintering.