Structural disorder versus chiral magnetism inCr1/3NbS2

Abstract

The crystal structure of a disordered form of Cr 1/3 NbS2 has been characterized using diffraction and inelastic scattering of synchrotron radiation. In contrast to the previously reported symmetry (P6322), the crystal can be described by a regular twinning of an average P63 structure with three disordered positions of the Cr ions. Short-range correlations of the occupational disorder result in a quite intense and structured diffuse scattering; a static nature of the disorder was unambiguously attributed by the inelastic x-ray scattering. The diffuse scattering has been modeled using a reverse Monte-Carlo algorithm assuming a disorder of the Cr sub-lattice only. The observed correlated disorder of the Cr sub-lattice reduces the temperature of the magnetic ordering from 130 K to 88 K and drastically modifies the field dependence of the magnetization as it is evidenced by the SQUID magnetometery. We conclude, that in contrast to the helicoidal spin structure assumed for P6322 form, the compound under study is ferromagnetically ordered with a pronounced in-plane anisotropy.

Finite-Temperature Properties of Three-Dimensional Chiral Helimagnets

“…Figure 1(b) shows the temperature dependence of the magnetization for several values of magnetic field. We can see characteristic cusp structures near the transition temperature; a similar cusp has been observed in experiments [10,15,20,22] and has been obtained in a phenomenological theory [16]. Small step-like structures at low temperatures are due to the finite-size effect along the helical axis.…”

“…The analysis of this model has revealed characteristic magnetization curves, which have been observed in experiments on CrNb 3 S 6 [9,10,[20][21][22] and YbNi 3 Al 9 [13][14][15]. Temperature effect of the spin moment has been included phenomenologically [5,16] and magnetization, entropy and specific heat have been discussed.…”

Crystal and magnetic structures of Cr1∕3NbSe2 from neutron diffraction

“…This result implies that disorder in Cr subsystem and small nonequality in occupancy of the 2c and 2d Wyckoff sites (model II) cannot be completely excluded. Contrary to the previous works on M 1=3 NbX 2 , 13,21,24,25 we found that in Cr 1=3 NbSe 2 , Cr atoms are predominantly distributed over 2b Wyckoff site. Such a discrepancy may be associated with enhanced covalency of the Se bonds formed with Cr in comparison with the Cr-S bonds in Cr 1=3 NbS 2 .…”

“…9,28 However, contrary to the result of our refinement for Cr 1=3 NbSe 2 all the crystal structure studies for M 1=3 NbX 2 reported predominant occupation of the 2c Wyckoff site by M atoms. 13,21,24,25 Detailed inspection of the refined atomic coordinates obtained for model II makes us doubt that the crystal structure of Cr 1=3 NbSe 2 is truly non-centrosymmetric. Indeed in accordance with Ref.…”

“…20 A precise investigation of the crystal structure and magnetic characterization of disordered form of the Cr 1=3 NbS 2 single crystal revealed that Cr atoms disorder substantially affects magnetic ordering temperature as well as the magnetic ground state. 21 The role of structural factors in the formation of chiral magnetic soliton lattice in the intercalation compound Cr 1=3 NbS 2 has been emphasized by means of phenomenological calculations. 22 Despite the much interest to Cr 1=3 NbS 2 there is a lack of published data on the crystal structure of the Cr 1=3 22 where intercalated atoms may partially occupy 2c, 2b, or 2d Wyckoff positions.…”