Combined experimental and modeling studies of the magnetocaloric effect, ultrasound, and magnetostriction were performed on single-crystal samples of the spin-dimer system ${\mathrm{Sr}}_3{\mathrm{Cr}}_2{\mathrm{O}}_8$ in large magnetic fields to probe the spin-correlated regime in the proximity of the field-induced $XY$-type antiferromagnetic order also referred to as a Bose-Einstein condensate of magnons. The magnetocaloric effect, measured under adiabatic conditions, reveals details of the field-temperature $(H,T)$ phase diagram, a dome characterized by critical magnetic-fields $H_{c1}=30.4,H_{c2}=62\mathrm{T}$, and a single maximum ordering temperature $T_{\max }\left(45\mathrm{T}\right)\simeq 8\mathrm{K}$. The sample temperature was observed to drop significantly as the magnetic field is increased, even for initial temperatures above $T_{\max }$, indicating a significant magnetic entropy associated with the field-induced closure of the spin gap. The ultrasound and magnetostriction experiments probe the coupling between the lattice degrees of freedom and the magnetism in ${\mathrm{Sr}}_3{\mathrm{Cr}}_2{\mathrm{O}}_8$. Our experimental results are qualitatively reproduced by a minimalistic phenomenological model of the exchange striction by which sound waves renormalize the effective exchange couplings.

We report on a comprehensive investigation of the effects of strain and film thickness on the structural and magnetic properties of epitaxial thin films of the prototypal $J_{\mathrm{eff}}=1/2$ compound ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ by advanced x-ray scattering. We find that the ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ thin films can be grown fully strained up to a thickness of 108 nm. By using x-ray resonant scattering, we show that the out-of-plane magnetic correlation length is strongly dependent on the thin film thickness, but independent of the strain state of the thin films. This can be used as a finely tuned dial to adjust the out-of-plane magnetic correlation length and transform the magnetic anisotropy from two-dimensional to three-dimensional behavior by incrementing film thickness. These results provide a clearer picture for the systematic control of the magnetic degrees of freedom in epitaxial thin films of ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ and bring to light the potential for a rich playground to explore the physics of $5d$ transition-metal compounds.

Low-dimensional materials manifest structural anisotropy, quantum confinement, and tightly bound excitonic states, which make them attractive building blocks that can be assembled within three-dimensional laterally stitched heterostructures, stacked van der Waals solids, and complex moiré superlattices. Ion intercalation in the galleries between layered materials provides a means of modifying interlayer separation and coupling, but it is also known to drive the shearing of the layers. In this article, we explore the distinct ligand coordination environments afforded by vanadyl oxygens of singular [V₄O₁₀] sheets and examine how the size, polarizability, and stoichiometry of Group I cations sandwiched between such layers determine the interlocking of the sheets in stacked structures. Based on the topochemical insertion of alkali-metal ions into the layered λ-V₂O₅, we identify seven types of guest ion coordination sites discretized into four distinct regimes of interlayer shear in units of half octahedral widths. The coordination preferences of intercalated cations govern how they interlock 2D [V₄O₁₀] sheets and engender specific shear conformations. We present evidence that static and dynamic disorder in guest ion arrangement modulate the magnetic structure of the intercalated compounds based on electrostatic polarization, localization of charge and spin density, and lattice distortion. The results illustrate the use of topochemical ion insertion to modulate stacking relationships and magnetic transition characteristics.

In this work, we investigate the evolution and settling of magnon condensation in the spin-1/2 dimer system ${\mathrm{Sr}}_3{\mathrm{Cr}}_2{\mathrm{O}}_8$ using a combination of magnetostriction in pulsed fields and inelastic neutron scattering in a continuous magnetic field. The magnetic structure in the Bose-Einstein condensation phase was probed by neutron diffraction in pulsed magnetic fields up to 39 T. The magnetic structure in this phase was confirmed to be an $\mathit{XY}$-antiferromagnetic structure validated by irreducible representational analysis. The magnetic phase diagram as a function of an applied magnetic field for this system is presented. Furthermore, zero-field neutron diffraction results indicate that dimerization plays an important role in stabilizing the low-temperature crystal structure.

We have synthesized single-crystal samples of $\beta \text{−}{\mathrm{VOSO}}_4$ and fully characterized their magnetic properties. Our magnetic susceptibility, high field magnetization, and powder inelastic neutron scattering results are in excellent agreement with theoretical expressions for a one-dimensional spin-1/2 Heisenberg chain with an exchange parameter of $3.83\left(2\right)$ meV. Ab initio calculations identify the superexchange pathway, revealing that the spin-chain does not run along the expected crystallographic chain $a$ direction but instead between ${\mathrm{V}}^{4+}{\mathrm{O}}_6$ octahedra that are linked via ${\mathrm{SO}}_4$ tetrahedra along the $b$ axis. We do not detect any phase transition to a long-range magnetic order within our experimental conditions, indicating $\beta \text{−}{\mathrm{VOSO}}_4$ is very close to an ideal one-dimensional magnetic system.