arXiv subjects

Zeno Maesen

Publications and source records attributed to Zeno Maesen.

3 recordsLinked to original sources

arXiv2026

Resolving growth-induced off-stoichiometry in AgCrSe$_2$ single crystals

The layered delafossite-like antiferromagnet AgCrSe$_2$ is a superionic conductor at high temperatures and has been reported to exhibit anomalous Hall behavior and Kondo physics at low temperatures. These extraordinary transport properties have been established almost exclusively on single crystals grown by chemical vapor transport, raising questions about the role of growth-induced off-stoichiometry. Using elemental analysis, single-crystal X-ray diffraction, and magnetization measurements, we show that such crystals are indeed systematically off-stoichiometric, with a general composition of Ag$_{1-x}$Cr(Se$_{2-y}$Cl$_y$) ($x \approx y \approx 0.08$) arising from the use of CrCl$_3$ as a transport agent. This off-stoichiometry manifests in altered magnetic properties, most notably a suppressed Néel temperature of 46\,K compared to 58\,K in stoichiometric polycrystalline samples prepared by solid-state synthesis. By optimizing an Ag/Se self-flux growth method, we obtained large single crystals of AgCrSe$_2$ that recover the magnetic transition temperature and saturation field of stoichiometric powder samples. These results establish self-flux growth as a route to high-quality stoichiometric AgCrSe$_2$ single crystals and provide a reliable platform for reassessing whether the reported anomalous transport phenomena are intrinsic or arise from off-stoichiometry.

cond-mat.mtrl-sci↗

arXiv2026

Coupled sawtooth chain exchange network in olivine Mn$_2$GeO$_4$

Sawtooth chain magnets have been a subject of historical interest in the field of frustrated magnetism, with classical olivine family $M_2TX_4$, ($M$ - 3d, $T$ - 4p, $X$ - chalcogen elements) typically realizing simple $\mathbf{k} = (000)$ states. The magnetism of the Mn$_2$GeO$_4$ olivine is surprisingly complex, proceeding from commensurate states to a multiferroic commensurate + incommensurate phase. Here we report inelastic neutron scattering results from a Mn$_2$GeO$_4$ single crystal and develop an effective Hamiltonian including long-distance bilinear and dipolar interactions. The magnetic interactions are predominantly antiferromagnetic and span a three-dimensional exchange network consisting of coupled sawtooth chains. Based on the determined strength of the couplings, the dominant sawtooth chains appear at third- and fourth- rather than next-nearest-neighbor. However the next-nearest-neighbor interaction is, along with a modest Dzyaloshinskii-Moriya interaction, important for modeling the observed incommensurability. We use the best-fit Hamiltonian as the basis for Langevin dynamics simulations and Luttinger-Tisza calculations of the high-temperature commensurate transition.

cond-mat.str-el↗

arXiv2024

Absence of altermagnetic magnon band splitting in MnF$_2$

Altermagnets are collinear compensated magnets in which the magnetic sublattices are related by rotation rather than translation or inversion. One of the quintessential properties of altermagnets is the presence of split chiral magnon modes. Recently, such modes have been predicted in MnF$_2$. Here, we report inelastic neutron scattering results on an MnF$_2$ single-crystal along high-symmetry Brillouin zone paths for which the magnon splitting is expected. Within the resolution of our measurement, we do not observe the predicted splitting. The inelastic spectrum is well-modeled using $J_1, ~J_2, ~J_3$ nearest-neighbor exchange interactions with weak uniaxial anisotropy. These interactions have higher symmetry than the crystal lattice, while the interactions predicted to produce the altermagnetic splitting are negligibly small. Therefore, the two magnon modes appear to be degenerate over the entire Brillouin zone and the spin dynamics of MnF$_2$ is indistinguishable from a classical Néel antiferromagnet. Application of magnetic field causes a Zeeman splitting of the magnon modes close to the $\mathrmΓ$ point. Even if chiral magnon modes are allowed by altermagnetic symmetry, the splitting in real materials such as MnF$_2$ can be negligibly small.

cond-mat.str-el↗