Synthesis and Characterization of Half-Metal Magnetic Materials Based on Transition Metal Chalcogenides

  The unique properties of two-dimensional (2D) transition metal chalcogenides (TMCs) have driven extensive research efforts focused on their synthesis, characterization, and applications. TMCs exhibit exceptional mechanical, electronic, optical, and magnetic properties, making them suitable for applications in energy storage, catalysis, flexible electronics, and spintronics. Among these materials, 2D magnetic TMCs have emerged as a promising class for spintronic applications due to their tunable electronic and magnetic behaviors, including ferromagnetic, antiferromagnetic, and half-metallic states. Their synthesis using chemical vapor deposition (CVD) offers advantages such as scalability, uniformity, and precise control over thickness and composition, paving the way for the development of novel spintronic devices.

Spintronics utilizes the electron`s intrinsic spin, in addition to its charge, to enable advanced functionalities in data storage and processing. Magnetic Random Access Memory (MRAM), a key application of spintronics, employs magnetic states for data retention, offering benefits such as non-volatility, rapid switching speeds, and low power consumption, making it a superior alternative to traditional memory technologies. Developing next-generation spintronic devices, including energy-assisted magnetic recording and fourth-generation MRAM, demands innovative materials with optimized half-metallic properties. Half-metals, which exhibit metallic conductivity for one spin orientation and insulating or semiconducting behavior for the opposite spin, are uniquely suited for these applications. Their 100% spin polarization enables highly efficient spin current generation, reducing energy losses and enhancing signal-to-noise ratios in MRAM. By ensuring minimal energy dissipation and enabling faster, more reliable switching, half-metals significantly improve MRAM performance, paving the way for more efficient and scalable spintronic memory technologies.

Cr2Se3 is proposed as the first experimentally realizable half-metallic antiferromagnet. Synthesized via ambient pressure chemical vapor deposition, ultrathin Cr2Se3 nanocrystals exhibited rhombohedral structures, high crystallinity, and antiferromagnetic behavior with a Néel temperature of 46 K. Density functional theory confirmed its half-metallicity, showing metallic and semiconducting spin channels. Magnetic tunnel junctions demonstrated spin-polarized conduction, while Josephson junctions revealed spin-triplet superconductivity. These results establish Cr2Se3 as a promising material for spintronic applications, offering 100% spin-polarized currents with zero net magnetization.

Cobalt sulfides represent another promising class of materials, characterized by diverse structural phases and magnetic properties, including half-metallic ferromagnetism in CoS2. This study developed an ambient pressure chemical vapor deposition method to synthesize 2D cobalt sulfides (CoS2, Co3S4, and CoS) with controlled phases. Structural characterization through using optical microscopy, atomic force microscopy, Raman spectroscopy, and transmission electron microscopy confirmed the high crystallinity of the synthesized nanocrystals. Phase control was achieved by adjusting synthesis parameters such as temperature and sulfur concentration, enabling transitions from pyrite CoS2 to cubic Co3S4 and hexagonal CoS. Magnetic measurements revealed ferromagnetic behavior in CoS2, with a Curie temperature of 123 K, while Co3S4 and CoS exhibited non-magnetic phases. Magneto-transport studies demonstrated metallic behavior across all phases, with CoS2 showing an anomalous Hall effect below Curie temperature.

Keywords : transition metal chalcogenides, chemical vapor deposition, half-metal, Cr₂Se₃, cobalt sulfides