Neutron diffraction and μSR studies of two polymorphs of nickel niobate NiNb2O6

Abstract

Neutron diffraction and muon spin relaxation (µSR) studies are presented for the newly characterized polymorph of NiNb2O6 (β-NiNb2O6) with space group P42/n and µSR data only for the previously known columbite structure polymorph with space group Pbcn. The magnetic structure of the P42/n form was determined from neutron diffraction using both powder and single crystal data. Powder neutron diffraction determined an ordering wave vector k = ( 1 2 , 1 2 , 1 2 ). Single crystal data confirmed the same k-vector and showed that the correct magnetic structure consists of antiferromagnetically-coupled chains running along the a or b-axes in adjacent Ni 2+ layers perpendicular to the c-axis, which is consistent with the expected exchange interaction hierarchy in this system. The refined magnetic structure is compared with the known magnetic structures of the closely related tri-rutile phases, NiSb2O6 and NiTa2O6. µSR data finds a transition temperature of TN ∼ 15 K for this system, while the columbite polymorph exhibits a lower TN = 5.7(3) K. Our µSR measurements also allowed us to estimate the critical exponent of the order parameter β for each polymorph. We found β = 0.25(3) and 0.16(2) for the β and columbite polymorphs respectively. The single crystal neutron scattering data gives a value for the critical exponent β = 0.28(3) for β-NiNb2O6, in agreement with the µSR value. While both systems have β values less than 0.3, which is indicative of reduced dimensionality, this effect appears to be much stronger for the columbite system. In other words, although both systems appear to well-described by S = 1 spin chains, the interchain interactions in the β-polymorph are likely much larger.

Correlated barrier charge hopping and non-Debye relaxation in columbite MnNb2O6

“…Usually, the A site atom is divalent and the Nb/Ta atoms are pentavalent; both the divalent and pentavalent cations are surrounded by six oxygen atoms forming slightly distorted octahedra of AO 6 and NbO 6 /TaO 6 . These octahedra are stacked in the following series: -A-Nb/Ta-Nb/Ta-A-Nb/Ta-Nb/Ta-A-along the a-axis and forms zig-zag chains along the caxis by sharing their edges [5,7,8,[11][12][13]. Further, the A site atoms arrange into a perfect isosceles triangular geometry in the ab-plane of the crystal which has been reported diagrammatically in our recent work [10,14].…”

Determination of the tricritical point, H–T phase diagram and exchange interactions in the antiferromagnet MnTa2O6

“…The transition metal compounds with general chemical formula AB 2 O 6 (A = Mn, Fe, Co, Ni and B = Nb, Ta) crystallize in the orthorhombic crystal structure of columbite (FeNb 2 O 6 ) with four molecular formula per unit cell [1][2][3][4][5] except FeTa 2 O 6 ,CoTa 2 O 6 and NiTa 2 O 6 which crystallize into tetragonal (tri-rutile) crystal structure with two molecular formula per unit cell [6][7][8][9]. In AB 2 O 6 compounds usually A and B sites are occupied by divalent and pentavalent cations respectively, forming octahedra [AO 6 andBO 6 ] with six oxygen atoms [3,5]. These compounds have potential applications in the field of satellite and mobile communications as dielectric resonators and filters [6,[10][11][12], as electrochemical gas sensors [6,13], and in supercapacitors [6,12].…”

In situ observation of the magnetocaloric effect through neutron diffraction in the Tb(DCO2)3 and TbODCO3 frameworks

“…There is also great fundamental interest in magnetic phenomena that emerge with increasing applied magnetic fields, including metamagnetic spin-flop and spin-flip transitions, [12][13][14][15][16] exotic magnetic states in Ising 1D chains and magnetisation plateaus. [17][18][19][20][21] Since the bulk magnetic properties of a material are ultimately driven by the atomic level structure, 8,22 understanding how the magnetic correlations in materials changes under applied magnetic fields is essential for innovation.…”