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1. Atomically Modulating Competing Exchange Interactions in Centrosymmetric Skyrmion Hosts GdRu ₂ X ₂ (X = Si and Ge)

   https://doi.org/10.1002/aelm.202500622  

   Rathnaweera, Dasuni N; Huai, Xudong; Kumar, K Ramesh; Winiarski, Michał J; Klimczuk, Tomasz; Iwanicki, Allana G; Kushwaha, Satya K; Mourigal, Martin; McQueen, Tyrel M; Tran, Thao T (May 2026, Advanced Electronic Materials)

   ABSTRACT Magnetic skyrmions are topologically protected spin states that hold promise for shaping the future of electronics. Despite impressive progress in skyrmion research, the microscopic mechanisms underlying skyrmion phase transitions at specific temperatures and magnetic fields remain elusive. In this work, we systematically study the isostructural centrosymmetric magnets GdRu₂X₂(X = Si and Ge) and the role of X‐porbitals in modifying magnetic exchange interactions. Electronic structure and exchange interaction evaluations reveal that the more extended Ge‐4pversus Si‐3porbitals enhance competing exchange interactions in GdRu₂Ge₂, thereby manifesting the evolution condition of skyrmions in GdRu₂X₂. GdRu₂Ge₂single crystals exhibit two high‐entropy regions associated with skyrmion phases at 0.9 T ≤µ₀H≤ 1.2 T and 1.3 T ≤µ₀H≤ 1.7 T, 2 K ≤T≤ 30 K—lower field and higher temperature conditions than those in the Si counterpart. Transport measurements reveal the topological Hall effect, validating the topologically nontrivial spin textures and Berry curvature. Our work bridges the gap between skyrmion discovery and material design by demonstrating, for the first time, how atomic‐scale control of exchange interactions enables tunable skyrmion phase transitions, making a significant step toward stabilizing skyrmions at desired temperatures and magnetic fields. 

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2. Giant topological Hall effect in centrosymmetric tetragonal Mn2−xZnxSb

   Md Rafique Un Nabi, Aaron Wegner (November 2021, Physical review)

   Topological magnetism typically appears in noncentrosymmetric compounds or compounds with geometric frustration. Here, we report the effective tuning of magnetism in centrosymmetric tetragonal Mn2−xZnxSb by Zn substitution. The magnetism is found to be closely coupled to the transport properties, giving rise to a very large topological Hall effect with fine-tuning of Zn content, which even persists to high temperature (∼250K). The further magnetoentropic analysis suggests that the topological Hall effect is possibly associated with topological magnetism. Our finding suggests Mn2−xZnxSb is a candidate material for a centrosymmetric tetragonal topological magnetic system, offering opportunities for studying and tuning spin textures and developing near room temperature spin-based devices. 

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3. Structural trends and itinerant magnetism of the new cage-structured compound HfMn₂Zn₂₀

   https://doi.org/10.1088/1361-648X/ad3875  

   Yasmin, Nusrat; Noor, Md_Fahel Bin; Besara, Tiglet (April 2024, Journal of Physics: Condensed Matter)

   Abstract A new cage-structured compound—HfMn₂Zn₂₀—belonging to theAB₂C₂₀ (A, B= transition or rare earth metals, andC= Al, Zn, or Cd) family of structures has been synthesized via the self-flux method. The new compound crystallizes in the space group $Fd\overline{3}m$ with lattice parameter a≈14.0543(2) Å (Z= 8) and exhibits non-stoichiometry due to Mn/Zn mixing on the Mn-site and an underoccupied Hf-site. The structure refines to Hf_0.93Mn_1.63Zn_20.37and follows lattice size trends when compared to other HfM₂Zn₂₀(M= Fe, Co, and Ni) structures. The magnetic measurements show that this compound displays a modified Curie-Weiss behavior with a transition temperature around 22 K. The magnetization shows no saturation, a small magnetic moment, and near negligible hysteresis, all signs of itinerant magnetism. The Rhodes–Wohlfarth ratio and the spin fluctuation parameters ratio both confirm the itinerant nature of the magnetism in HfMn₂Zn₂₀. 

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4. Observation of Topological Spin Textures in Ferrimagnetic Mn2-xZnxSb

   https://doi.org/10.1002/smll.202406299  

   Li, Yue; Nabi, Md_Rafique Un; Park, Hyowon; Liu, Yuzi; Rosenkranz, Stephan; Petford‐Long, Amanda K; Hu, Jin; Velthuis, Suzanne_GE te; Phatak, Charudatta (April 2025, Small)

   Abstract Ferrimagnets, which have both ferromagnetic and antiferromagnetic coupling, are attracting increased attention in the realm of spintronic devices due to advantages such as ultrafast dynamics and a suppressed skyrmion Hall effect. Thus, understanding the behavior of nontrivial spin textures in ferrimagnets is crucial; however, comprehensive reports on this topic remain limited. Here, the magnetic spin textures of ferrimagnetic Mn_{2 −x}Zn_xSb (x = 0.85) is explored as a function of temperature and applied magnetic field. The spin textures can be tuned to a variety of states, including stripes, skyrmion bags, and a skyrmion lattice. Chiral Néel‐type magnetic structures are visualized using Lorentz transmission electron microscopy. Mn(I) ions are slightly shifted toward the Sb sites, which may be due to a strong electrostatic interaction between Mn and Sb ions. This local structural distortion breaks the inversion symmetry and introduces an effective Dzyaloshinkii–Moriya interaction. This work thus provides a pathway to use doping and heterogeneity in a ferrimagnet to control and generate chiral nontrivial spin textures. 

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5. Medium‐Entropy Engineering of Magnetism in Layered Antiferromagnet Cu _x Ni _{2(1‐ x )} Cr _x P ₂ S ₆

   https://doi.org/10.1002/adfm.202418722  

   Upreti, Dinesh; Basnet, Rabindra; Sharma, M M; Chhetri, Santosh Karki; Acharya, Gokul; Nabi, Md_Rafique Un; Sakon, Josh; Benamara, Mourad; Mortazavi, Mansour; Hu, Jin (December 2024, Advanced Functional Materials)

   Abstract Antiferromagnetic van der Waals‐typeM₂P₂X₆compounds provide a versatile material platform for studying 2D magnetism and relevant phenomena. Establishing ferromagnetism in 2D materials is technologically valuable. Though magnetism is generally tunable via a chemical way, it is challenging to induce ferromagnetism with isovalent chalcogen and bimetallic substitutions inM₂P₂X₆. Here, we report co‐substitution of Cu¹⁺and Cr³⁺for Ni²⁺in Ni₂P₂S₆, creating Cu_xNi_2(1‐x)Cr_xP₂S₆medium‐entropy alloys spanning a full substitution range (x= 0 to 1). Such substitution strategy leads to a unique evolution in crystal structure and magnetic phases that are distinct from traditional isovalent bimetallic doping, with Cu and Cr co‐substitution enhancing ferromagnetic correlations and generating a weak ferromagnetic phase in intermediate compositions. This aliovalent substitution strategy offers a universal approach for tuning layered magnetism in antiferromagnetic systems, which along with the potential for light‐matter interaction and high‐temperature ferroelectricity, can enable multifunctional device applications. 

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