Study of the quasi two-dimensional CoxNi1-xTa2O6 compounds by X-ray diffraction and magnetic susceptibility measurements

Abstract

International audienceWe report results on the structural and magnetic properties of the CoxNi1-xTa2O6 series of compounds by X-ray powder diffraction, magnetic susceptibility and magnetization measurements. X-ray refinements carried out by the Rietveld method show that these compounds crystallize in a P42/mnm tetragonal structure. Magnetic susceptibility curves show a broadened maximum witnessing that these compounds exhibit two-dimensional antiferromagnetic behaviors. All the CoxNi1-xTa2O6 compounds order below 10 K and present a large ion anisotropy. The magnetic properties have been determined in both the paramagnetic and antiferromagnetic state. In the hypothesis of two dimensional AF ordering, the near neighbor exchange constants (J1) and the next near neighbor exchange constants for two different paths (J2 and J'2) were determined. The composition dependence of the magnetic properties including ordering temperature, exchange constants and anisotropy factors are discussed. The drastic reduction of the ordering temperature for x=0.20 for CoxNi1-xTa2O6, suggest the hypothesis of a peculiar magnetic behavior for this composition

Magnetic, thermal, and optical properties of single-crystalline CoTa2O6and FeTa2O6and their anisotropic magnetocaloric effect

“…Kremer et al [5] found 4.74 J mol -1 K -1 , which led them to conclude that the Co 2+ ions are in the low-spin configuration. However, a low-spin state for Co 2+ disagrees with the conclusion of S = 3/2, drawn from the magnetization (see also [8] and [34]), which is a direct measurement of µ eff . The low value for ∆S suggests that a large fraction of the (high-spin) moments remain magn etically disordered as T → 0.…”

Strongly correlated one-dimensional magnetic behavior ofNiTa2O6

“…The magnetic properties of NiTa 2 O 6 have been the subject of a number of studies, but a unanimous consensus especially on the appropriate spin-exchange model has not been reached until now. [21][22][23][24][25][26][27][28][29][30] Previous magnetization measurements have reported Curie-Weiss behavior with Curie-Weiss temperatures ranging from -19.9 K to -50 K indicating a predominant AFM SEI. [21,22,29] Long-range AFM ordering was consistently reported to appear below 11 K. [23,24,28,30] The magnetic structure has been previously determined by powder neutron diffraction revealing a rather large magnetic unit cell (propagation vector (1/4, -1/4, 1/2)) with the magnetic moments being collinearly aligned parallel to [1 1 0].…”

“…[21][22][23][24][25][26][27][28][29][30] Previous magnetization measurements have reported Curie-Weiss behavior with Curie-Weiss temperatures ranging from -19.9 K to -50 K indicating a predominant AFM SEI. [21,22,29] Long-range AFM ordering was consistently reported to appear below 11 K. [23,24,28,30] The magnetic structure has been previously determined by powder neutron diffraction revealing a rather large magnetic unit cell (propagation vector (1/4, -1/4, 1/2)) with the magnetic moments being collinearly aligned parallel to [1 1 0]. [25] The ordered moment was refined to 1.6 µ B and the difference to the expected moment of g × m S ∼ 2 µ B was attributed to incomplete ordering of the spins.…”

Structural Metamorphosis and Band Dislocation of Trirutile NiTa2O6 under Compression

“…The phase attributes of NiTa 2 O 6 for structural footprint are confirmed initially by XRD pattern with Rietveld refinement, as shown in Figure a. All sharp peaks are fitted well with the tetragonal system with the space group P 42/ mnm and point group D 4h 14 , and no secondary or impurity peaks were detected in the XRD spectrum . The goodness of fitting (χ 2 ), conventional reliability factor R wp , and R exp were found to be 1.09, 15, and 14.37, respectively.…”

“…All sharp peaks are fitted well with the tetragonal system with the space group P42/mnm and point group D 4h 14 , and no secondary or impurity peaks were detected in the XRD spectrum. 37 The goodness of fitting (χ 2 ), conventional reliability factor R wp , and R exp were found to be 1.09, 15, and 14.37, respectively. The refined lattice, structural parameters, and bond lengths of NiTa 2 O 6 were compared and well correspond with previously published result 38 in Table 1 To shed more light on structural properties, the XPS spectrum in a wide energy range is shown in Figure 2a.…”