Exploring ternary molybdenum nitrides as candidate quantum magnets for hosting skyrmions

Abstract

The magnetic quasi-particles called Skyrmions, discovered in the year 2009, are known to have many unique and intriguing properties that are predicted to be very useful in the field of spintronics. However, in order to realize efficient room-temperature devices that make use of Skyrmions an appropriate host material is needed. In this project, we have explored a family of ternary molybdenum nitrides as potential Skyrmion host materials. We optimized the synthesis process to obtain Ni2Mo3N, Fe0.75Ni1.25Mo3N, Fe0.5Ni1.5Mo3N,

Fe0.4Pd0.1Ni1.5Mo3N as nearly single-phase compositions (i.e. with a minimal amount of sec- ondary phases present, if any). Structural characterisation was done using powder x-ray

diffraction and a field emission scanning electron microscope. Rietveld refinement was per- formed to further analyse the crystal structure. For Ni2Mo3N and Fe0.75Ni1.25Mo3N, the

specific heat capacity, Magnetic susceptibility, and resistivity were measured in the low tem- perature range; and resistivity and seebeck coefficient were measured in the high-temperature

range. Ni2Mo3N shows the absence of long-range magnetic ordering down to a temperature of 2 K. However, when some of the Ni is substituted with Fe, the resulting compound Fe0.75Ni1.25Mo3N shows a ferromagnetic ordering at 150 K. This ferromagnetic transition was evidenced as a sharp rise of the magnetic susceptibility below 150 K. The samples Fe0.5Ni1.5Mo3N and Fe0.4Pd0.1Ni1.5Mo3N, when dipped in liquid nitrogen, exhibit a strong attraction to a permanent magnet. This shows that they also have a ferromagnetic ordering above liquid nitrogen temperature. However, their detailed magnetic properties are yet to be evaluated.