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ObjectivesKnee joint distraction (KJD) is a novel, but poorly understood, treatment for osteoarthritis (OA) associated with remarkable ‘spontaneous’ cartilage repair in which resident synovial fluid (SF) multipotential mesenchymal stromal cells (MSCs) may play a role. We hypothesised that SF hyaluronic acid (HA) inhibited the initial interaction between MSCs and cartilage, a key first step to integration, and postulate that KJD environment favoured MSC/cartilage interactions.MethodsAttachment of dual-labelled SF-MSCs were assessed in a novel in vitro human cartilage model using OA and rheumatoid arthritic (RA) SF. SF was digested with hyaluronidase (hyase) and its effect on adhesion was observed using confocal microscopy. MRI and microscopy were used to image autologous dual-labelled MSCs in an in vivo canine model of KJD. SF-HA was investigated using gel electrophoresis and densitometry.ResultsOsteoarthritic-synovial fluid (OA-SF) and purified high molecular weight (MW) HA inhibited SF-MSC adhesion to plastic, while hyase treatment of OA-SF but not RA-SF significantly increased MSC adhesion to cartilage (3.7-fold, p<0.05) These differences were linked to the SF mediated HA-coat which was larger in OA-SF than in RA-SF. OA-SF contained >9 MDa HA and this correlated with increases in adhesion (r=0.880). In the canine KJD model, MSC adhesion to cartilage was evident and also dependent on HA MW.ConclusionsThese findings highlight an unappreciated role of SF-HA on MSC interactions and provide proof of concept that endogenous SF-MSCs are capable of adhering to cartilage in a favourable biochemical and biomechanical environment in OA distracted joints, offering novel one-stage strategies towards joint repair.

Exchange interactions are mediated via orbital overlaps across chemical bonds. Thus, modifying the bond angles by physical pressure or strain can tune the relative strength of competing interactions. Here we present a remarkable case of such tuning between the Heisenberg ( J ) and Kitaev ( K ) exchange, which respectively establish magnetically ordered and spin liquid phases on a honeycomb lattice. We observe a rapid suppression of the Néel temperature ( T N ) with pressure in Ag 3 LiRh 2 O 6 , a spin-1/2 honeycomb lattice with both J and K couplings. Using a combined analysis of x-ray data and first-principles calculations, we find that pressure modifies the bond angles in a way that increases the ∣ K / J ∣ ratio and thereby suppresses T N . Consistent with this picture, we observe a spontaneous onset of muon spin relaxation ( μ SR) oscillations below T N at low pressure, whereas in the high pressure phase, oscillations appear only when T  <  T N /2. Unlike other candidate Kitaev materials, Ag 3 LiRh 2 O 6 is tuned toward a quantum critical point by pressure while avoiding a structural dimerization in the relevant pressure range. Kitaev interactions on a honeycomb lattice can potentially lead to a quantum spin liquid state. Unfortunately, materials hosting Kitaev interactions also host Heisenberg interactions favouring long range order. Here, Sakrikar, Shen, Poldi and coauthors find that the relative strength of the Heisenberg and Kitaev interactions can be tuned by pressure in Ag 3 LiRh 2 O 6 .

The S  = 1/2 triangular lattice antiferromagnet (TLAF) is a paradigmatic example of frustrated quantum magnetism. An ongoing challenge involves understanding the influence of exchange anisotropy on the collective behavior within such systems. Using inelastic neutron scattering (INS) and advanced calculation techniques, we have studied the low and high-temperature spin dynamics of Ba 2 La 2 CoTe 2 O 12 (BLCTO): a Co 2+ -based J eff  = 1/2 TLAF that exhibits 120° order below T N  = 3.26 K. We determined the spin Hamiltonian by fitting the energy-resolved paramagnetic excitations measured at T  >  T N , revealing exceptionally strong easy-plane XXZ anisotropy. Below T N , the excitation spectrum exhibits a high energy continuum having a larger spectral weight than the single-magnon modes, suggesting a scenario characterized by a spinon confinement length that markedly exceeds the lattice spacing. We conjecture that this phenomenon arises from the proximity to a quantum melting point, even under strong easy-plane XXZ anisotropy. Finally, we highlight characteristic flat features in the excitation spectrum, which are connected to higher-order van Hove singularities in the magnon dispersion directly induced by easy-plane XXZ anisotropy. Our results provide a rare experimental insight into the nature of highly anisotropic S  = 1/2 TLAFs between the Heisenberg and XY limits. A TLAF is an archetypal geometrically frustrated magnetic system, which serves as the foundation for many exotic states, including quantum spin-liquids. Here, Park et al perform INS measurements on BLCTO, which, combined with theoretical calculations, reveal distinctive fingerprints of spinon excitations, thereby suggesting proximity to a spin liquid even in the presence of strong XXZ anisotropy.

The observation of high- T c superconductivity (HTSC) in concomitant with pressure-induced orthorhombic-tetragonal structural transition in bilayer La 3 Ni 2 O 7 has sparked hopes of achieving HTSC by stabilizing the tetragonal phase at ambient pressure. Chemical pressure, introduced by replacing La 3+ with smaller rare-earth R 3+ has been considered as a potential route. However, our experimental and theoretical investigation reveals that such substitutions, despite causing lattice contraction, actually produce stronger orthorhombic distortions, requiring higher pressures for the structural transition. A linear extrapolation of P c versus the average size of A -site cations (< r A >), yields a putative critical value of < r A > c ≈ 1.23 Å for P c ≈ 1 bar. The negative correlation between P c and < r A > indicates that replacing La 3+ with smaller R 3+ ions is unlikely to reduce P c to ambient pressure. Instead, substituting La 3+ with larger cations like Sr 2+ or Ba 2+ might be a feasible approach. Our results provide guidance for realizing ambient-pressure HTSC in bilayer nickelates.

Pb M O 3 ( M  = 3 d transition metals) family shows systematic variations in charge distribution and intriguing physical properties due to its delicate energy balance between Pb 6 s and transition metal 3 d orbitals. However, the detailed structure and physical properties of PbFeO 3 remain unclear. Herein, we reveal that PbFeO 3 crystallizes into an unusual 2 a p  × 6 a p  × 2 a p orthorhombic perovskite super unit cell with space group Cmcm . The distinctive crystal construction and valence distribution of Pb 2+ 0.5 Pb 4+ 0.5 FeO 3 lead to a long range charge ordering of the -A-B-B- type of the layers with two different oxidation states of Pb (Pb 2+ and Pb 4+ ) in them. A weak ferromagnetic transition with canted antiferromagnetic spins along the a -axis is found to occur at 600 K. In addition, decreasing the temperature causes a spin reorientation transition towards a collinear antiferromagnetic structure with spin moments along the b -axis near 418 K. Our theoretical investigations reveal that the peculiar charge ordering of Pb generates two Fe 3+ magnetic sublattices with competing anisotropic energies, giving rise to the spin reorientation at such a high critical temperature. PbFeO 3 is part of a family of lead based perovskites with many intriguing properties; however, difficulties in synthesis have hampered investigation. Here, the authors present a detailed study of the structure of PbFeO 3 observing unique charge ordering and spin orientation among the constituent ions.

The Na2Co3(AsO4)2(OH)2 structure has garnered interest owing to its mix of two-dimensional honeycomb and Kagome lattice features to form a Kagome-strip motif of S = 3/2 high-spin Co2+ metal centers. The Kagome-strip is believed to possess the same magnetically frustrated interactions as its parent honeycomb and Kagome lattices, both of which are well-known for their high magnetic frustration potential. Single crystals of Na2Co3(AsO4)2(OH)2 were prepared via a hydrothermal method. The pink columnar crystals crystallize in C2/m with cell parameters of a = 14.5885(9), b = 5.9376(3), and c = 5.0992(3) Å with β = 103.63(2)°. Magnetization studies show antiferromagnetic ordering at 14 K that is suppressed through a metamagnetic antiferro- to ferromagnetic transition that occurs at applied fields greater than 40 kOe, as revealed by isothermal field-dependent magnetization studies below 14 K. Magnetic structure determination by powder neutron diffraction yielded a k-vector of (0.5,0.5,0.5), confirming the antiferromagnetic behavior in low-field magnetization. Both Co(1) and Co(2) moments lie in the bc-plane. Specifically, the Co(1) moments point along the c-axis, while the Co(2) moments rest along the b-axis. Magnetic studies presented herein suggest a highly frustrated system with complimentary powder neutron diffraction data providing a pathway for additional transition metal arsenate and vanadate analogs each with their own unique magnetic interactions owing to a difference in the transition metals themselves and in the interaction pathways afforded through p- and d-orbitals in the respective arsenate and vanadates.

Local magnetic ordering and anisotropy is often central to the emergent behavior and subsequent functional properties in quantum materials and beyond. Neutron powder diffraction provides a straightforward yet extremely powerful technique for quantitative measurements of microscopic magnetic properties. The HB-2A powder diffractometer located at the High Flux Isotope Reactor in ORNL is traditionally utilized for long-range magnetic structure determination. Recently these capabilities have been extended to include methods aimed at accessing local magnetism: Half- polarized neutron powder diffraction (pNPD) and magnetic pair distribution function (mPDF) analysis. These two distinct techniques are possible on HB-2A due to the versatility of the instrument’s reciprocal space coverage, resolution and novel ultra-low temperature multi-sample changers that operate down to dilution refrigerator temperatures. This provides unique capabilities not found on any powder diffraction instrument and is particularly well suited to investigations of magnetic quantum materials. The development and implementation of these techniques will be discussed with a series of science case examples ranging from geometric frustrated magnets to magnetic metal-organic frameworks. Data reduction and analysis tools will be presented that enable the extraction of the local site susceptibility tensor and local spin-spin correlations in real space. Finally, potential combinations of these techniques in the form of half-polarized magnetic pair distribution function (pmPDF) analysis will be considered. Looking forward, HB-2A is undergoing a detector upgrade that will be in the user program by 2026. This will offer an order of magnitude increase in count rates to further aid the development of these often low signal measurements and provide new scientific capabilities.

Two-dimensional layered materials, where magnetic layers are linked through van der Waals (vdW) bonding provides a promising platform for spintronics applications and quantum behavior. However, realizing their full potential requires a deeper understanding of their spin behavior across different length scales. In this study, we investigated the local magnetic correlations of bulk antiferromagnetic vdW materials MnPSe3, MnPS3 and CrPS4 using neutron scattering using the magnetic pair distribution function (mPDF) technique. We explore short-range magnetic correlations in a systematic series of MnPSxSe3-x (x=0, 1, 1.5, 2,3) powder samples with neutron total scattering data. Our results reveal that substituting S/Se anions, despite being non-magnetic, tunes both atomic structure and enables the gradual modulation of magnetic correlation length and spin angle. Complementary inelastic neutron scattering measurement further quantify changes in the magnetic exchange interactions, highlighting the continuous evolution of spin correlations across the series. Additionally, short-range magnetic correlations of CrPS4 were analyzed and modeled using the mPDF technique in the paramagnetic regime, under both zero-field and applied magnetic field conditions.

We investigate the magnetic ground state of CuNdO 2 , which is a delafossite with a triangular lattice of magnetic Nd 3+ ions that are well separated by non-magnetic Cu spacer layers. From inelastic neutron scattering measurements of the crystal electric field, we determine the strong Ising character of the pseudo-spin 1/2 Nd 3+ moments. Magnetic susceptibility and heat capacity measurements reveal the onset of long-range antiferromagnetic order at T N = 0.78 K. While the magnetic transition is definitively observed with muon spin relaxation, accompanied by the formation of a weakly dispersing spin wave excitation, no dipole-ordered moment is detected with neutron diffraction. We show that the apparent absence of a dipolar ordered moment is a consequence of the dominant Ising character of the antiferromagnetically coupled Nd 3+ moments, which experience extreme frustration on the triangular lattice. Consequently, the frustration in CuNdO 2 is relieved through in-plane ordering of the substantially smaller perpendicular component of the Nd 3+ moments into a 120° structure, with a nearly vanishing ordered moment.