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Diluted magnetic semiconductor (DMS) systems have been extensively studied in recent decades. DMSs provides a platform where charge transport and magnetic ordering phenomena exhibit unique interplays, together with possible applications to spin-dependent electronics (spintronics) devices. Initial development of ferromagnetic (FM) DMS systems centered around III-V semiconductors doped with dilute transition metals, such as (Ga,Mn)As, obtained by co-doping of spin and charge. More recently, independent spin and charge doping was first achieved in Li(Zn,Mn)As, a DMS system based on I-II-V semiconductor, with charge doping via variable Li concentrations and spin doping via iso-valent (Zn,Mn) substitutions. Although more than 30 new DMS systems with independent spin and charge doping have been synthesized since then, the main research emphasis has been put on development and characterization of systems with higher FM Curie temperature (TC) and different crystal structures suitable for possible formation of heterostructure devices. This article focuses on a new DMS material Na(Zn,Mn)Sb, which exhibits a spin glass (SG) ordering, together with metal-insulator transition (MIT) and colossal negative magnetoresistance (CMR) as a function of independent spin and charge doping and application of external magnetic fields. MIT and CMR phenomena are elucidated by magneto transport, magnetization, angle resolved photoemission spectroscopy (ARPES), and scanning tunneling microscopy (STM) measurements, and by band calculations which demonstrate development and disappearance of energy gap. Magnetic order and dynamic spin fluctuations are probed with muon spin relaxation (μSR) and magnetization, and the results for Na(Zn,Mn)Sb are compared to those from FM DMS systems Li(Zn,Mn)As, Li(Zn,Mn)P, and Li(Zn,Mn,Cu)As. First-principles calculations are performed for Na(Zn,Mn)Sb, (Ga,Mn)As and Li(Zn,Mn)P to highlight the roles of charge and spin doping on exchange interactions mediated by nearest neighbor super-exchange coupling and oscillatory Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling via conduction electrons. These studies reveal (1) MIT and CMR of Na(Zn,Mn)Sb manifest as a response to spin configurations as spin-driven transport phenomena; (2) a dynamic critical behavior is observed in SG transition of Na(Zn,Mn)Sb, in contrast to more first-order-like magnetic evolutions in other FM DMS systems; (3) charge doping supports FM coupling additive to direct AFM exchange interaction between nearest-neighbor Mn pairs; and (4) a widely different coercive fields seen in different families of FM and SG DMS systems can be explained by geometrical frustration of AFM interaction in underlying lattice for Mn spin network 

Refractory complex concentrated alloys (RCCAs) show potential as the next-generation structural materials due to their superior strength in extreme environments. However, RCCAs processed by metal additive manufacturing (AM) typically suffer from process-related challenges surrounding laser material interaction defects and microstructure control. Multimodal in situ techniques (synchrotron X-ray imaging and diffraction and infrared imaging) and melt pool-level simulations were employed to understand rapid solidification pathways in two representative RCCAs: (i) multi-phase BCC + HCP Ti0.4Zr0.4Nb0.1Ta0.1 and (ii) single-phase BCC Ti0.486V0.375Cr0.111Ta0.028. As expected, laser material interaction defects followed similar systematic trends in process parameter space for both alloys. Additionally, both alloys formed a single-phase (BCC) microstructure after rapid solidification processing. However, significant differences in microstructure selection between these alloys were discovered, where Ti0.4Zr0.4Nb0.1Ta0.1 showed a mixture of equiaxed and columnar grains, while Ti0.486V0.375Cr0.111Ta0.028 was dominated by columnar growth. These behaviors were well described by the influence of undercooling effects on columnar-to-equiaxed transition (CET). Distinct microstructure formation in each alloy was verified through CET predictions via analytical melt pool simulations, which showed a ~ 5 × increase degrees in undercooling for Ti0.4Zr0.4Nb0.1Ta0.1 compared to Ti0.486V0.375Cr0.111Ta0.028. Overall, these results show that microstructure control based on modulating the freezing range must be balanced with process considerations which resist defect formation, such as solidification crack formation in RCCAs. 

Despite the critical role of sintering phenomena in constraining the long-term durability of nano-sized particles, a clear understanding of nanoparticle sintering has remained elusive due to the challenges in atomically tracking the neck initiation and discerning different mechanisms. Through the integration of in-situ transmission electron microscopy and atomistic modeling, this study uncovers the atomic dynamics governing the neck initiation of Pt-Fe nanoparticles via a surface self-diffusion process, allowing for coalescence without significant particle movement. Real-time imaging reveals that thermally activated surface morphology changes in individual nanoparticles induce significant surface self-diffusion. The kinetic entrapment of self-diffusing atoms in the gaps between closely spaced nanoparticles leads to the nucleation and growth of atomic layers for neck formation. This surface self-diffusion-driven sintering process is activated at a relatively lower temperature compared to the classic Ostwald ripening and particle migration and coalescence processes. The fundamental insights have practical implications for manipulating the morphology, size distribution, and stability of nanostructures by leveraging surface self-diffusion processes.