Evidence of Paracrystalline Cation Order in the Ruddlesden-Popper Phase LaSr3NiRuO8 through Neutron Total Scattering Techniques

Ligand solid-solution tuning of magnetic and mechanical properties of the van der Waals metal-organic magnet NiCl2(btd)1-x(bod)x

Van der Waals (vdW) magnets offer unique opportunities for exploring magnetism in the 2D limit. Metal-organic magnets (MOM) are of particular interest as the functionalisation of organic ligands can control their physical properties. Here, we demonstrate tuning of mechanical and magnetic function of a noncollinear vdW ferromagnet, NiCl2(btd) (btd = 2,1,3-benzothiadiazole), through creating solid-solutions with the oxygen-substituted analogue ligand 2,1,3-benzoxadiazole (bod). We synthesise NiCl2(btd)1-x(bod)x up to x = 0.33, above which we find mixtures primarily composed of 1D NiCl2(bod)2. Magnetometry reveals bod incorporation reduces the coercivity significantly (up to 60%), without altering the ordering temperatures. High pressure synchrotron diffraction measurements up to 0.4 GPa demonstrate that the stiffest axis is the b axis, through the Ni-N-(O/S)-N-Ni bonds, and the softest is the interlayer direction. Doping with bod fine-tunes this compressibility, softening the layers, but stiffening the interlayer axis. This demonstrates that substitution of organic ligands in vdW MOMs can be used to realise targeted magnetic and mechanical properties.

Strategies and Considerations for Least-Squares Analysis of Total Scattering Data

The process of least-squares analysis has been applied for decades in the field of crystallography. Here, we discuss the application of this process to total scattering data, primarily in the combination of least-squares Rietveld refinements and fitting of the atomic pair distribution function (PDF). While these two approaches use the same framework, the interpretation of results from least-squares fitting of PDF data should be done with caution through carefully constructed analysis approaches. We provide strategies and considerations for applying least-squares analysis to total scattering data, combining both crystallographic Rietveld and fitting of PDF data, given in context with recent examples from the literature. This perspective is aimed to be an accessible document for those new to the total scattering approach, as well as a reflective framework for the total scattering expert.

Hole and Electron Doping of Topochemically Reduced Ni(I)/Ru(II) Insulating Ferromagnetic Oxides

La_xSr_2-xNiRuO₆, La_xSr_4-xNiRuO₈, and La_xSr_3-xNiRuO₇ are, respectively, the n = ∞, 1, and 2 members of the (La_x/2Sr_1-(x/2))_nSr(Ni_0.5Ru_0.5)_nO_3n+1 compositional series. Reaction with CaH₂, in the case of the La_xSr_2-xNiRuO₆ perovskite phases, or Zr oxygen getters in the case of the La_xSr_4-xNiRuO₈ and La_xSr_3-xNiRuO₇ Ruddlesden-Popper phases, yields the corresponding topochemically reduced (La_x/2Sr_1-(x/2))_nSr(Ni_0.5Ru_0.5)_nO_3n-1 compounds (La_xSr_2-xNiRuO₄, La_xSr_4-xNiRuO₆, and La_xSr_3-xNiRuO₅), which contain Ni and Ru cations in square-planar coordination sites. The x = 1 members of each series (LaSrNiRuO₄, LaSr₃NiRuO₆, and LaSr₂NiRuO₅) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni¹⁺ and Ru²⁺ centers they contain. Increasing the La³⁺ concentration (x > 1) leads to a reduction of some of the Ru²⁺ centers to Ru¹⁺ centers and a suppression of the ferromagnetic state (lower T_c, reduced saturated ferromagnet moment). In contrast, increasing the Sr²⁺ concentration (x < 1) oxidizes some of the Ru²⁺ centers to Ru³⁺ centers and enhances the ferromagnetic coupling (increased T_c, increased saturated ferromagnet moment) for the n = ∞ and n = 2 samples but appears to have no influence on the magnetic ordering temperature of the n = 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.