arXiv subjects

N. Biniskos

Publications and source records attributed to N. Biniskos.

9 recordsLinked to original sources

arXiv2025

Spin structures and phase diagrams of the spin-$\frac{5}{2}$ triangular-lattice antiferromagnet Na$_2$BaMn(PO$_4$)$_2$ under magnetic field

We combine single-crystal neutron diffraction studies and Monte Carlo simulations to determine the spin structures and finite-temperature phase diagram of the spin-5/2 triangular-lattice antiferromagnet Na$_2$BaMn(PO$_4$)$_2$ in magnetic field. With the application of a magnetic field in two different directions, namely along the $c$-axis and in the $ab$-plane of the trigonal symmetry, we track the evolution of the spin structure through changes of the magnetic propagation vector. We account for these results with a minimal Heisenberg Hamiltonian that includes easy-axis anisotropy and weak, frustrated interlayer couplings in addition to intralayer exchange. Guided by representation analysis, we refine symmetry-allowed modes to the measured intensities and obtain the spin structures for all field-induced phases, which we compare quantitatively with simulated configurations. Taken together, our measurements and simulations show that frustrated interlayer exchange -- rather than purely 2D physics -- organizes the unexpectedly rich field-induced phases of Na$_2$BaMn(PO$_4$)$_2$.

cond-mat.str-el↗

arXiv2024

Paramagnetic fluctuations of the magnetocaloric compound MnFe$_4$Si$_3$

Inelastic neutron scattering technique is employed to investigate the paramagnetic spin dynamics in a single crystalline sample of the magnetocaloric compound MnFe$_4$Si$_3$. In the investigated temperature range, 1.033$\times T_{C}$ to 1.5$\times T_{C}$, where $T_C$ is the Curie temperature, the spin fluctuations are well described by the ferromagnetic Heisenberg model predictions. Apart from the Heisenberg exchange, additional pseudo-dipolar interactions manifest through a finite long-wavelength relaxation rate that vanishes at the transition temperature ($T_C = 305$\,K). Based on the characteristic extend of spin fluctuations in wave-vector and energy space we determine that the nature of magnetism in MnFe$_4$Si$_3$ is localized above room temperature. This contrasts with the most celebrated Mn and Fe based magnetocaloric materials that are considered as itinerant magnets.

cond-mat.mtrl-sci↗

arXiv2023

Topological magnons driven by the Dzyaloshinskii-Moriya interaction in the centrosymmetric ferromagnet Mn$_5$Ge$_3$

The phase of the quantum-mechanical wave function can encode a topological structure with wide-ranging physical consequences, such as anomalous transport effects and the existence of edge states robust against perturbations. While this has been exhaustively demonstrated for electrons, properties associated with the elementary quasiparticles in magnetic materials are still underexplored. Here, we show theoretically and via inelastic neutron scattering experiments that the bulk ferromagnet Mn$_5$Ge$_3$ hosts gapped topological Dirac magnons. Although inversion symmetry prohibits a net Dzyaloshinskii-Moriya interaction in the unit cell, it is locally allowed and is responsible for the gap opening in the magnon spectrum. This gap is predicted and experimentally verified to close by rotating the magnetization away from the $c$-axis with an applied magnetic field. Hence, Mn$_5$Ge$_3$ realizes a gapped Dirac magnon material in three dimensions. Its tunability by chemical doping or by thin film nanostructuring defines an exciting new platform to explore and design topological magnons. More generally, our experimental route to verify and control the topological character of the magnons is applicable to bulk centrosymmetric hexagonal materials, which calls for systematic investigation.

cond-mat.str-el↗

arXiv2023

An overview of the spin dynamics of antiferromagnetic Mn$_5$Si$_3$

The metallic compound Mn$_5$Si$_3$ hosts a series of antiferromagnetic phases which can be controlled by external stimuli such as temperature and magnetic field. In this work, we investigate the spin-excitation spectrum of bulk Mn$_5$Si$_3$ by combining inelastic neutron scattering measurements and density functional theory calculations. We study the evolution of the dynamical response under external parameters and demonstrate that the spin dynamics of each phase is robust against any combination of temperature and magnetic field. In particular, the high-energy spin dynamics is very characteristic of the different phases consisting of either spin waves or broad fluctuations patterns.

cond-mat.mtrl-sci↗

arXiv2022

Unconventional short-range structural fluctuations in cuprate high-$T_c$ superconductors

The interplay between structural and electronic degrees of freedom in complex materials is the subject of extensive debate in physics and materials science. Particularly interesting questions pertain to the nature and extent of pre-transitional short-range order in diverse systems ranging from shape-memory alloys to unconventional superconductors, and how this microstructure affects macroscopic properties. Here we use neutron and X-ray diffuse scattering to uncover universal structural fluctuations in La$_{2-x}$Sr$_x$CuO$_4$ and Tl$_2$Ba$_2$CuO$_{6+δ}$, two cuprate superconductors with distinct point disorder effects and optimal superconducting transition temperatures. The fluctuations are present in wide doping and temperature ranges, including compositions that maintain high average structural symmetry, and they exhibit unusual, yet simple scaling behavior. The scaling regime is robust and universal, similar to the well-known critical fluctuations close to second-order phase transitions, but with a distinctly different physical origin. We relate this behavior to pre-transitional phenomena in a broad class of systems with structural and magnetic transitions, and propose an explanation based on rare structural fluctuations caused by intrinsic nanoscale inhomogeneity. We also uncover parallels with superconducting fluctuations, which indicates that the underlying inhomogeneity plays an important role in cuprate physics.

cond-mat.supr-con↗

arXiv2021

Complex magnetic structure and spin waves of the noncollinear antiferromagnet Mn5Si3

The investigations of the interconnection between micro- and macroscopic properties of materials hosting noncollinear antiferromagnetic ground states are challenging. These forefront studies are crucial for unraveling the underlying mechanisms at play, which may prove beneficial in designing cutting edge multifunctional materials for future applications. In this context, Mn5Si3 has regained scientific interest since it displays an unusual and complex ground state, which is considered to be the origin of the anomalous transport and thermodynamic properties that it exhibits. Here, we report the magnetic exchange couplings of the noncollinear antiferromagnetic phase of Mn5Si3 using inelastic neutron scattering measurements and density functional theory calculations. We determine the ground-state spin configuration and compute its magnon dispersion relations which are in good agreement with the ones obtained experimentally. Furthermore, we investigate the evolution of the spin texture under the application of an external magnetic field to demonstrate theoretically the multiple field-induced phase transitions that Mn5Si3 undergoes. Finally, we model the stability of some of the material's magnetic moments under a magnetic field and we find that very susceptible magnetic moments in a frustrated arrangement can be tuned by the field.

cond-mat.mes-hall↗

arXiv2020

Spin-waves in the collinear antiferromagnetic phase of Mn$_\bf{5}$Si$_\bf{3}$

By combining two independent approaches, inelastic neutron scattering measurements and density functional theory calculations, we study the spin-waves in the high-temperature collinear antiferromagnetic phase (AFM2) of Mn$_5$Si$_3$. We obtain its magnetic ground-state properties and electronic structure. This study allowed us to determine the dominant magnetic exchange interactions and magnetocrystalline anisotropy in the AFM2 phase of Mn$_5$Si$_3$. Moreover, the evolution of the spin excitation spectrum is investigated under the influence of an external magnetic field perpendicular to the anisotropy easy-axis. The low energy magnon modes show a different magnetic field dependence which is a direct consequence of their different precessional nature. Finally, possible effects related to the Dzyaloshinskii-Moriya interaction are also considered.

cond-mat.mes-hall↗

arXiv2018

Total interference between nuclear and magnetovibrational one-phonon scattering cross sections

A full phonon intensity cancellation is reported in a longitudinal polarized inelastic neutron scattering experiment performed on the magnetocaloric compound MnFe$_{4}$Si$_{3}$, a ferromagnet with $T_{Curie}$ $\approx$ 305 K. The TA[100] phonon polarized along the $c$-axis measured from the Brillouin zone center $\textbf{G}$=(0, 0, 2) is observed only in one ($σ_{z}^{++}$) of the two non-spin-flip polarization channels and is absent in the other one ($σ_{z}^{--}$) at low temperatures. This effect disappears at higher temperatures, in the vicinity of $T_{Curie}$, where the phonon is measured in both channels with nonetheless marked different intensities. The effect is understood as originating from nuclear-magnetic interference between the nuclear one-phonon and the magnetovibrational one-phonon scattering cross-sections. The total cancellation reported is accidental, i.e. does not correspond to a systematic effect, as established by measurements in different Brillouin zones.

cond-mat.mtrl-sci↗

arXiv2018

Spin-fluctuations drive the inverse magnetocaloric effect in Mn5Si3

Inelastic neutron scattering measurements were performed on single crystals of the antiferromagnetic compound Mn5Si3 in order to investigate the relation between the spin dynamics and the magneto-thermodynamic properties. It is shown that among the two stable antiferromagnetic phases of this compound, the high temperature one has an unusual magnetic excitation spectrum where propagative spin-waves and diffuse spin-fluctuations coexist. Moreover, it is evidenced that the inverse magnetocaloric effect of Mn5Si3, the cooling by adiabatic magnetization, is associated with field induced spin-fluctuations.

cond-mat.mtrl-sci↗