Al Maha Al Habsi

This work demonstrates the synthesis of ferromagnetic metallic cobalt nanoparticles embedded in a graphene framework through a graphene-assisted carbothermal reduction process. Cobalt oxide (Co₃O₄) was employed as the starting material, with graphene nanopowder functioning simultaneously as the reducing medium and structural scaffold. Thermal treatment at 850 °C under an argon atmosphere triggered the phase transformation. X-ray diffraction (XRD) confirmed the successful conversion of cobalt oxide into face-centered cubic (FCC) metallic cobalt. The graphene network not only accelerated the reduction reaction but also ensured the homogeneous distribution of cobalt nanoparticles within the matrix. Magnetic measurements using vibrating sample magnetometry (VSM) revealed a substantial improvement in ferromagnetic behavior: the graphene-mediated samples reached a saturation magnetization (M_s) of approximately 130 emu/g, compared to the nearly non-magnetic response of cobalt oxide annealed under the same conditions without graphene. Collectively, the structural, compositional, and magnetic results highlight graphene’s critical role in driving the formation of metallic cobalt nanoparticles with enhanced ferromagnetism, emphasizing their promise for use in magnetic storage, sensing, and spintronic applications. We anticipate that this study will inspire further research into the dual functionality of graphene, serving as both a reductive agent for metal oxides and a supportive matrix for nanoparticles, toward enhancing the structural integrity and functional properties of graphene-based metal nanocomposite materials.

In this study, we investigate the thermal pinning and depinning behaviors of vortex domain walls (VDWs) in constricted magnetic nanowires, with a focus on potential applications in storage memory nanodevices. Using micromagnetic simulations and spin transfer torque, we examine the impacts of device temperature on VDW transformation into a transverse domain wall (TDW), mobility, and thermal strength pinning at the constricted area. We explore how thermal fluctuations influence the stability and mobility of domain walls within stepped nanowires. The thermal structural stability of VDWs and their pinning were investigated considering the effects of the stepped area depth (d) and its length (λ). Our findings indicate that the thermal stability of VDWs in magnetic stepped nanowires increases with decreasing the depth of the stepped area (d) and increasing nanowire thickness (th). For th ≥ 50 nm, the stability is maintained at temperatures ≥ 1200 K. In the stepped area, VDW thermal pinning strength increases with increasing d and decreasing λ. For values of d ≥ 100 nm, VDWs depin from the stepped area at temperatures ≥ 1000 K. Our results reveal that thermal effects significantly influence the pinning strength at constricted sites, impacting the overall performance and reliability of magnetic memory devices. These insights are crucial for optimizing the design and functionality of next-generation nanodevices. The stepped design offers numerous advantages, including simple fabrication using a single electron beam lithography exposure step on the resist. Additionally, adjusting λ and d allows for precise control over the pinning strength by modifying the dimensions of the stepped areas.