Incommensurate antiferromagnetic order in weakly frustrated two-dimensional van der Waals insulator CrPSe3_3

Although the magnetic order is suppressed by a strong magnetic frustration, it is maintained but appears in complex order forms such as a cycloid or spin density wave in weakly frustrated systems. Herein, we report a weakly magnetic-frustrated two-dimensional van der Waals material CrPSe$_3$. Polycrystalline CrPSe$_3$ was synthesized at an optimized temperature of 700$^\circ$C to avoid the formation of any secondary phases (e.g., Cr$_2$Se$_3$). The antiferromagnetic transition appeared at $T_N\sim 126$ K with a large Curie-Weiss temperature $T_{\rm CW} \sim -371$ via magnetic susceptibility measurements, indicating weak frustration in CrPSe$_3$ with a frustration factor $f (|T_{\rm CW}|/T_N) \sim 3$. Evidently, the formation of long-range incommensurate spin-density wave antiferromagnetic order with the propagation vector $k = (0, 0.04, 0)$ was revealed by neutron diffraction measurements at low temperatures (below 120K). The monoclinic crystal structure of C2/m symmetry is preserved over the studied temperature range down to 20K, as confirmed by Raman spectroscopy measurements. Our findings on the spin density wave antiferromagnetic order in two-dimensional (2D) magnetic materials, not previously observed in the MPX$_3$ family, are expected to enrich the physics of magnetism at the 2D limit, thereby opening opportunities for their practical applications in spintronics and quantum devices.Comment: 23 pages, 4 figures, 2 table

Structural and magnetic properties of Cr2O3\mathrm{Cr_{2}O_{3}} at high pressure

The structural and magnetic properties of Cr$_{2}$O$_{3}$ have been studied by means of X-ray and neutron powder diffraction at high pressures up to 35 GPa. The lattice compression of the rhombohedral crystal structure of R $\bar{3}$c symmetry is slightly anisotropic with anomaly in the pressure behavior of the c/a parameters ratio at P $\approx$ 20 GPa of presumably magnetic nature. The oxygen octahedra around chromium ions become more symmetric with close values of shared and unshared bonds under high pressure. The antiferromagnetic structure of Cr$_{2}$O$_{3}$ remains stable in the studied pressure range up to 35 GPa. The pressure coefficient of the Neel temperature, (1/T$_N$)(dT$_N$/dP) = + 0.0091 GPa$^1$, is significantly less in comparison with perovskite-like compounds containing Cr$^{3+}$ and Mn$^{4+}$ ions of similar electronic configuration

The Polymorphic Phase Transformations in the Chlorpropamide under Pressure

The crystal structure and vibrational spectra of the chlorpropamide have been studied by means of the X-ray diffraction andRaman spectroscopy at pressures up to 24.6 and 4.4 GPa, respectively. Two polymorphic phase transitions, between initial orthorhombicform-A and a monoclinic form-AI at P ∼ 1.2 GPa and, in additional, to another monoclinic form-AII at P ∼ 3.0 GPa, were observed.At pressures above 9.6 GPa, a transformation to the amorphous phase of chlorpropamide was revealed. The lattice parameters, unit cellvolumes, and vibration modes as functions of pressure were obtained for the different polymorphic modifications of chlorpropamide

Magneto-orbital texture in the perovskite modification of Mn2O3

Crystal and magnetic structures of the high-pressure-stabilized perovskite modification of Mn2O3 (ζ -Mn2O3) have been studied by neutron powder diffraction combined with symmetry arguments based on the phenomenological Landau theory. This metastable phase exhibits a unique charge disproportionation phenomenon stabilizing the quadruple perovskite structure (Mn2+Mn3+ 3 )Mn3.25+ 4 O12 with an additional charge-ordering and commensurate orbital density wave localized in the B-site perovskite position. The commensurate nature of the orbital density wave is stimulated by a coupling of the orbital ordering to independent structural distortions, which improve poor bonding conditions of Mn2+ in the A-site perovskite position. Below T1 ∼ 100 K, an anharmonic longitudinal spin density wave arises and locks to the structural modulation associated with the orbital density. At T2 ∼ 50 K, the magnetic subsystem delocks from the structural modulation giving rise to a multi-k phase-modulated ground state admixing cycloidal and helical components. The complex anharmonic and phase-modulated magnetic structures are discussed based on a phenomenological magneto-orbital coupling scheme, previously developed to explain the multi-k helical ground states with modulated spin chirality observed in A2+Mn7O12 (A2+ = Ca, Sr, Pb, and Cd) quadruple perovskite

Spin-induced multiferroicity in the binary perovskite manganite Mn2O3

The ABO3 perovskite oxides exhibit a wide range of interesting physical phenomena remaining in the focus of extensive scientific investigations and various industrial applications. In order to form a perovskite structure, the cations occupying the A and B positions in the lattice, as a rule, should be different. Nevertheless, the unique binary perovskite manganite Mn2O3 containing the same element in both A and B positions can be synthesized under high-pressure high-temperature conditions. Here, we show that this material exhibits magnetically driven ferroelectricity and a pronounced magnetoelectric effect at low temperatures. Neutron powder diffraction revealed two intricate antiferromagnetic structures below 100 K, driven by a strong interplay between spin, charge, and orbital degrees of freedom. The peculiar multiferroicity in the Mn2O3 perovskite is ascribed to a combined effect involving several mechanisms. Our work demonstrates the potential of binary perovskite oxides for creating materials with highly promising electric and magnetic properties

Pressure-induced polar phases in relaxor multiferroic PbFe0.5Nb0.5O3PbFe_{0.5}Nb_{0.5}O_{3}

The structural, magnetic, and vibrational properties of PbFe0.5Nb0.5O3 relaxor multiferroic have been studied by means of x-ray, neutron powder diffraction, and Raman spectroscopy at pressures up to 30 GPa. Two successive structural phase transitions from the initial R3m polar phase to Cm and Pm monoclinic polar phases were observed at P = 5.5 and 8.5 GPa. Both transitions are associated with anomalies in pressure behavior of several stretching and bending modes of oxygen octahedra as well as Fe/Nb localized vibrationalmodes. The G-type antiferromagnetic order remains stable upon compression up to 6.4 GPa, assuming possible multiferroic properties of pressure-induced phases. The Neel temperature increases with a pressure coefficient ´(1/TN)dTN/dP = 0.012 GPa−1. The observed pressure-induced phenomena in PbFe0.5Nb0.5O3 are in drasticcontrast with conventional multiferroics, exhibitin

An intermediate antipolar phase in NaNbO3NaNbO_{3} under compression

The crystal structure and vibration spectra of sodium niobate NaNbO$_3$ have been studied by means of neutron diffraction, X-ray diffraction and Raman spectroscopy at high pressures. An isostructural phase transformation from the initial antiferroelectric phase to an intermediate antiferroelectric phase HP-I have been observed under 2 GPa. This transformation is caused by complex reorientations of NbO$_6$ octahedra. Subsequent structural phase transition from the phase HP-I to an orthorhombic phase HP-III have been detected at pressures above 10 GPa. This transition leads to suppression of an antiferroelectric state of NaNbO$_3$. The observed phase transitions are accompanied by anomalies in lattice parameters compression

High Pressure-Driven Magnetic Disorder and Structural Transformation in Fe3GeTe2: Emergence of a Magnetic Quantum Critical Point

Copyright © 1999-2023 John Wiley & Sons, Inc. All rights reserved. Among the recently discovered 2D intrinsic van der Waals (vdW) magnets, Fe3GeTe2 (FGT) has emerged as a strong candidate for spintronics applications, due to its high Curie temperature (130 - 220 K) and magnetic tunability in response to external stimuli (electrical field, light, strain). Theory predicts that the magnetism of FGT can be significantly modulated by an external strain. However, experimental evidence is needed to validate this prediction and understand the underlying mechanism of strain-mediated vdW magnetism in this system. Here, the effects of pressure (0 - 20 GPa) are elucidated on the magnetic and structural properties of Fe3GeTe2 by means of synchrotron Mossbauer source spectroscopy, X-ray powder diffraction and Raman spectroscopy over a wide temperature range of 10 - 290 K. A strong suppression of ferromagnetic ordering is observed with increasing pressure, and a paramagnetic ground state emerges when pressure exceeds a critical value, P-PM approximate to 15 GPa. The anomalous pressure dependence of structural parameters and vibrational modes is observed at P-C approximate to 7 GPa and attributed to an isostructural phase transformation. Density functional theory calculations complement these experimental findings. This study highlights pressure as a driving force for magnetic quantum criticality in layered vdW magnetic systems.11Nsciescopu

Pressure-Induced Modifications of the Magnetic Order in the Spin-Chain Compound Ca\u3csub\u3e3\u3c/sub\u3eCo\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e6\u3c/sub\u3e

The structural and magnetic properties of the Ca3Co2O6 spin-chain compound have been studied by means of neutron and x-ray powder diffraction at pressures up to 6.8 and 32 GPa, respectively. A suppression of the initial spin-density wave state (TN = 25 K) and stabilization of the collinear commensurate antiferromagnetic (AFM) state at high pressures (TNC = 26 K at P = 2.1 GPa) were observed. The pressure behavior of the competing intra- and interchain magnetic interactions was analyzed on the basis of obtained structural data and their role in the formation of the magnetic phase diagram is discussed. The pressure behavior of the Néel temperature of the commensurate AFM phase was evaluated within the mean field theory approach and a good agreement with the experimental value dTNC/dP = 0.65 K/GPa was obtained

Structural, magnetic and vibrational properties of multiferroic GaFeO3GaFeO_{3} at high pressure

The crystal, magnetic structure and vibrational spectra of multiferroic GaFeO$_3$ have been studied by means of neutron, X-ray powder diffraction and Raman spectroscopy at pressures up to 6.2 and 42 GPa, respectively. A presence of Fe/Ga antisite disorder leads to a formation of the ferrimagnetic ground state with the Néel temperature T$_N$ = 292 K at ambient pressure. Upon compression, the magnetic ground state symmetry remains the same and the Néel temperature increases with a pressure coefficient (1/T$_N$)(dT$_N$/dP) = 0.011(1) GPa$^{−1}$. Application of high pressure above 21 GPa leads to a gradual structural phase transition from the polar orthorhombic Pc2$_1$n phase to nonpolar orthorhombic Pbnm phase. It is accompanied by anomalies in the pressure behaviour of several Raman modes. Pressure dependencies of lattice parameters and Raman modes frequencies in the observed structural phases were obtained