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1. Field tunable magnetic transitions of CsCo ₂ (MoO ₄ ) ₂ (OH): a triangular chain structure with a frustrated geometry

   https://doi.org/10.1039/d2qm01272c  

   Sanjeewa, Liurukara D.; Garlea, V. Ovidiu; Fishman, Randy S.; Foroughian, Mahsa; Yin, Li; Xing, Jie; Parker, David S.; Smith Pellizzeri, Tiffany M.; Sefat, Athena S.; Kolis, Joseph W. (March 2023, Materials Chemistry Frontiers)

   The sawtooth chain compound CsCo 2 (MoO 4 ) 2 (OH) is a complex magnetic system and here, we present a comprehensive series of magnetic and neutron scattering measurements to determine its magnetic phase diagram. The magnetic properties of CsCo 2 (MoO 4 ) 2 (OH) exhibit a strong coupling to the crystal lattice and its magnetic ground state can be easily manipulated by applied magnetic fields. There are two unique Co 2+ ions, base and vertex, with J bb and J bv magnetic exchange. The magnetism is highly anisotropic with the b -axis (chain) along the easy axis and the material orders antiferromagnetically at T N = 5 K. There are two successive metamagnetic transitions, the first at H c 1 = 0.2 kOe into a ferrimagnetic structure, and the other at H c 2 = 20 kOe to a ferromagnetic phase. Heat capacity measurements in various fields support the metamagnetic phase transformations, and the magnetic entropy value is intermediate between S = 3/2 and 1/2 states. The zero field antiferromagnetic phase contains vertex magnetic vectors (Co(1)) aligned parallel to the b -axis, while the base vectors (Co(2)) are canted by 34° and aligned in an opposite direction to the vertex vectors. The spins in parallel adjacent chains align in opposite directions, creating an overall antiferromagnetic structure. At a 3 kOe applied magnetic field, adjacent chains flip by 180° to generate a ferrimagnetic phase. An increase in field gradually induces the Co(1) moment to rotate along the b -axis and align in the same direction with Co(2) generating a ferromagnetic structure. The antiferromagnetic exchange parameters are calculated to be J bb = 0.028 meV and J bv = 0.13 meV, while the interchain exchange parameter is considerably weaker at J ch = (0.0047/ N ch ) meV. Our results demonstrate that the CsCo 2 (MoO 4 ) 2 (OH) is a promising candidate to study new physics associated with sawtooth chain magnetism and it encourages further theoretical studies as well as the synthesis of other sawtooth chain structures with different magnetic ions. 

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2. Quantifying the orbital-to-spin moment ratio under dynamic excitation

   https://doi.org/10.1063/5.0198326  

   Emori, Satoru; Maizel, Rachel E.; Street, Galen T.; Jones, Julia L.; Arena, Dario A.; Shafer, Padraic; Klewe, Christoph (March 2024, Applied physics letters)

   The orbital component of magnetization dynamics, e.g., excited by ferromagnetic resonance (FMR), may generate “orbitronic” effects in nanomagnetic devices. Yet, distinguishing orbital dynamics from spin dynamics remains a challenge. Here, we employ x-ray magnetic circular dichroism (XMCD) to quantify the ratio between the orbital and spin components of FMR-induced dynamics in a Ni80Fe20 film. By applying the XMCD sum rules at the Ni L3,2 edges, we obtain an orbital-to-spin ratio of 0.108 ± 0.005 for the dynamic magnetization. This value is consistent with 0.102 ± 0.008 for the static magnetization, probed with the same x-ray beam configuration as the dynamic XMCD experiment. The demonstrated method presents a possible path to disentangle orbitronic effects from their spintronic counterparts in magnetic media. 

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3. Structural Inhomogeneities and Suppressed Magnetostructural Coupling in Mn-Substituted GeCo ₂ O ₄

   https://doi.org/10.1021/acs.chemmater.5c01331  

   Sharma, Shivani; Jain, Pooja; Schundelmier, Benny; Wang, Chin-Wei; Yadav, Poonam; Szucs, Adrienn Maria; Wei, Kaya; Lalla, Niranjan P; Siegrist, Theo (August 2025, Chemistry of Materials)

   A comprehensive study of the Ge1-xMn x Co2O4 (GMCO) system was conducted using neutron powder diffraction (NPD), X-ray diffraction (XRD), scanning electron microscopy, magnetometry, and heat capacity measurements. Comparative analysis with GeCo2O4 (GCO) highlights the influence of Mn substitution on crystal and magnetic structures at low temperatures. Surprisingly, phase separation is observed in GMCO with a targeted nominal composition with Ge/Mn close to 50:50. Scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) analysis reveals pronounced compositional inhomogeneities, which are not evident in the XRD data. The GMCO sample predominantly consists of a Mn-rich primary phase with approximate stoichiometry Mn0.74Ge0.18Co2O4, along with a minor Ge-rich secondary phase of composition Ge0.91Mn0.18Co2O4. Although both GCO and GMCO crystallize in cubic symmetry at room temperature, a substantial difference in low-temperature structural properties has been observed. Magnetic and heat capacity data indicate ferrimagnetic ordering in Mn0.74Ge0.18Co2O4 near T c = 108 K, while Ge0.91Mn0.18Co2O4 exhibits antiferromagnetic order at T N = 22 K. Analysis of heat capacity data reveals that the estimated magnetic entropy amounts to only 56\% of the theoretical value expected in GMCO. A collinear ferrimagnetic arrangement is observed in Mn0.74Ge0.18Co2O4 below the magnetic ordering temperature, characterized by antiparallel spins of Mn at the A site and Co at the B site along the c-direction. At 5 K, the refined magnetic moments are 2.31(3) mu B for MnA and 1.82(3) mu B for CoB in the Mn0.74Ge0.18Co2O4 phase. The magnetic structure at 5 K in Ge0.91Mn0.18Co2O4 is identical to the antiferromagnetic structure of the parent compound GeCo2O4. The refined value of the CoB moment in this phase at 5 K is 2.53(3) mu B. 

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4. Non-magnetic ion site disorder effects on the quantum magnetism of a spin-1/2 equilateral triangular lattice antiferromagnet

   https://doi.org/10.1088/1361-648X/ac5703  

   Huang, Q; Rawl, R; Xie, W W; Chou, E S; Zapf, V S; Ding, X X; Mauws, C; Wiebe, C R; Feng, E X; Cao, H B; et al (March 2022, Journal of Physics: Condensed Matter)

   Abstract With the motivation to study how non-magnetic ion site disorder affects the quantum magnetism of Ba 3 CoSb 2 O 9 , a spin-1/2 equilateral triangular lattice antiferromagnet, we performed DC and AC susceptibility, specific heat, elastic and inelastic neutron scattering measurements on single crystalline samples of Ba 2.87 Sr 0.13 CoSb 2 O 9 with Sr doping on non-magnetic Ba 2+ ion sites. The results show that Ba 2.87 Sr 0.13 CoSb 2 O 9 exhibits (i) a two-step magnetic transition at 2.7 K and 3.3 K, respectively; (ii) a possible canted 120 degree spin structure at zero field with reduced ordered moment as 1.24 μ B /Co; (iii) a series of spin state transitions for both H ∥ ab -plane and H ∥ c -axis. For H ∥ ab -plane, the magnetization plateau feature related to the up–up–down phase is significantly suppressed; (iv) an inelastic neutron scattering spectrum with only one gapped mode at zero field, which splits to one gapless and one gapped mode at 9 T. All these features are distinctly different from those observed for the parent compound Ba 3 CoSb 2 O 9 , which demonstrates that the non-magnetic ion site disorder (the Sr doping) plays a complex role on the magnetic properties beyond the conventionally expected randomization of the exchange interactions. We propose the additional effects including the enhancement of quantum spin fluctuations and introduction of a possible spatial anisotropy through the local structural distortions. 

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5. Single crystal synthesis and anisotropic magnetization of TMSb2O4 (TM = Mn, Co, Ni)

   https://doi.org/10.1016/j.jssc.2025.125400  

   Patel, Bhakti K; Powell, Matthew S; McMillen, Colin D; Kolis, Joseph W (September 2025, Journal of Solid State Chemistry)

   The synthesis, single crystal growth and anisotropic magnetization study of high-quality, single crystals in the TMSb2O4 (TM = Mn, Co, Ni) series are reported. Columnar crystals, several millimeters in length, crystallized in the tetragonal space group, P42/mbc, were obtained by a high-temperature hydrothermal method. Magnetization studies of crystals aligned in an external magnetic field respective to the principal crystallographic axes were performed and allowed study of the 1D intrachain interactions of octahedral TM2+ edge-shared chains along the c-axis, as well as the wider 3D magnetic superstructure arising from through-space interchain interactions. Magnetic susceptibility measurements revealed strong ordering behavior when fields were applied along the chains that were contrasted by a more muted response for chain orientations normal to the applied field. The field- and cooling-dependent ordering transitions found in the CoSb2O4 system when a field is applied perpendicular to the S = 3/2 Co2+ chains is complex and highlights the highly anisotropic spin exchange coupling between the intrachain, nearest-neighbor (NN), and next-nearest-neighbor (NNN) interactions. Specific heat measurements revealed a field-dependent secondary ordering feature at 13.5 K that, on application of 90 kOe applied fields, is suppressed and broadened, which matches behavior seen in the field-dependent susceptibility. The anisotropic magnetic coupling provides a roadmap for additional study of single crystals of other 1D chains.Not Available 

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