Lattice and spin dynamics in a low-symmetry antiferromagnet NiWO4

Abstract

Lattice and magnetic dynamics of NiWO4 single crystals were studied with the use of polarized Raman spectroscopy in a wide temperature range of 10-300 K including the antiferromagnetic ordering temperature TN =62 K. Static magnetic measurements were used for characterizing the single crystals. All Raman-active phonons predicted by the group theory were observed and characterized. Magnetic symmetry analysis was used to determine possible magnetic space groups for NiWO4 which can be also applied to any other isostructural crystal with the same magnetic propagation vector k=(1/2,0,0). Though the magnetic structure of NiWO4 is relatively simple, a rich set of narrow and broad magnetic excitations with different polarization properties and temperature behavior in the very broad frequency range of 10-200 cm −1 was observed, with some modes surviving at temperatures much higher than TN up to 220 K. Part of the magnetic excitations were identified as acoustic and optical spin-wave branches which allow us to construct exchange structure and estimate exchange and anisotropy constants with the use of linear spin-wave theory. Since the magnetic structure can be described as exchange-coupled AFM chains of S =1 ions, previously unobserved magnetic excitation at 24 cm −1 is tentatively assigned to a Haldane gap mode.

Nickel–cobalt bimetallic tungstate decorated 3D hierarchical porous carbon derived from lignin for high-performance supercapacitor applications

“…[47][48][49] Overall, both the XRD and Raman results indicate the successful synthesis of Ni 4Àx Co x WO 4 nanocomposites and their great potential for supercapacitor application. 47,50 Insight into the morphologies and microstructures of all materials was further obtained through scanning electron microscopy (SEM) analysis. As displayed in Fig.…”

“…26 Meanwhile, the other medium-intensity characteristic peaks appearing at 775, 690, 549, 418, 363, 213, and 134 cm −1 can also be assigned to Ni and Co in Ni 3 Co 1 WO 4 . 47–49 Overall, both the XRD and Raman results indicate the successful synthesis of Ni 4− x Co x WO 4 nanocomposites and their great potential for supercapacitor application. 47,50…”

“…47–49 Overall, both the XRD and Raman results indicate the successful synthesis of Ni 4− x Co x WO 4 nanocomposites and their great potential for supercapacitor application. 47,50…”

Lattice and magnetic dynamics in the polar, chiral, and incommensurate antiferromagnet Ni2InSbO6

“…Another part of phonons (plots (c) and (d)) manifest strong shifts by 2 cm −1 which is almost twice as large in comparison to hardening in the 10-300 K range due to anharmonicity. Such strong spinphonon coupling is not typical for small-spin (S = 1) systems for Ni 2+ [56,57], however comparable and even larger shifts were observed in Ni 3 TeO 6 [39]. Experimental values of spin-phonon constants λ are determined as a frequency difference of the phonon mode at the lowest temperature (10 K) and that predicted by anharmonic equation (Eq.…”

Preparation and Properties of a High-Entropy Wolframite-Type Antiferromagnet, (Mn0.2Co0.2Ni0.2Cu0.2Cd0.2)WO4

“…Wolframite-type compounds MWO 4 represent a very interesting class of antiferromagnetic (AFM) materials with Néel temperatures ( T N ) of 13.5 K (M = Mn), , 75 K (M = Fe), , 48 , or 42 K (M = Co), 60–62 K (M = Ni), ,, and 23–24 K (M = Cu). ,, The majority of them, together with diamagnetic analogues with M = Mg, Zn, and Cd, are monoclinic (space group P 2/ c ), but CuWO 4 exhibits triclinic distortion due to the Jahn–Teller effect. In MnWO 4 , there are actually two more phase transitions at about 12.5 and 7 or 8 K. The phase existing between these temperature is ferroelectric and, therefore, multiferroic. , A huge amount of work has been done on the structure and physical properties of individual wolframite-type compounds and their binary solid solutions, especially based on MnWO 4 , but they cannot be discussed in detail in this Communication.…”