Evidence for a frustrated square lattice with ferromagnetic nearest-neighbor interaction in the new compound Pb2VO(PO4)2

Magnetic correlation in the square-lattice spin system (CuBr)Sr2Nb3O10: A neutron diffraction study

“…The helical chains are coupled ferromagnetically along the a axis. The ordered moment is found to be 0.79(7) μ B /Cu 2+ -ion at 2 K. The observed helical AFM structure for the present square-lattice system (CuBr)Sr 2 Nb 3 O 10 is in contrast to the reported collinear AFM structure for other square-lattice systems, such as layered vanadium phosphates AA VO(PO 4 ) 2 with AA = Pb 2 , 27 BaZn, 28 SrZn, 29 PbZn, 16 and BaCd 30 with the FM J 1 and AFM J 2 . A helical AFM structure is also in contrast to the theoretically predicted magnetic states for the FM J 1 -J 2 model, namely, a collinear AFM structure for values of α (=|J 2 /J 1 |) 0.6, and a FM structure for α 0.4.…”

“…[15][16][17][18][19] A collinear AFM structure [Q = (π 0) or (0 π )] was found for (CuBr)LaNb 2 O 7 , 43 an n = 2 member of the present Dion-Jacobson series [(CuX)A n−1 B n O 3n+1 ] with FM J 1 and an α value of (J 2 /J 1 = 41.3 K/(−35.6 K)) = 1.1, which is well inside the range for a collinear AFM state (α 0.6). The other reported square-lattice compounds with FM J 1 having a collinear AFM structure, such as Pb 2 VO(PO 4 ) 2 (α ∼ 1.6) 27 and BaCdVO(PO 4 ) 2 (α ∼ 0.9), 30 are as well far above the lower limit of α 0.6. At the other extreme of α values [i.e., for compounds with lower values of J 2 /(FMJ 1 )], a FM state [Q = (0 0)] is predicted.…”

“…23,24 The square-lattice layered vanadium phosphate AA VO(PO 4 ) 2 with AA = Zn 2 also reveals AFM J 1 and J 2 . 25,26 On the other hand, the other layered vanadium phosphates AA VO(PO 4 ) 2 with AA = Pb 2 , 27 BaZn, 28 SrZn, 29 and BaCd 30 (with square-lattice spin arrangements) show the FM J 1 and AFM J 2 . A recent investigation shows that PbZnVO(PO 4 ) 2 also belongs to the square-lattice compound with FM J 1 and AFM J 2 .…”

Frustrated Magnetism in Vanadium Oxides

“…Recently various layered vanadium compounds have been found which correspond well to the J 1 −J 2 model. They are of the type Li 2 VOXO 4 (X = Si, Ge) [11,12] and AA VO(PO 4 ) 2 (A, A = Pb, Zn, Sr, Ba) [13,14] and consist of V-oxide pyramid layers containing V 4+ ions with S = 1/2. From the analysis of zero field thermodynamic results the frustration ratio J 2 /J 1 may be obtained, however an ambiguity remains [4].…”

Thermodynamic properties of the 2D frustrated Heisenberg model for the entire J1–J2 circle

“…Cuprates and numerous other quasi-2D compound with antiferromagnetic (AFM) nearestneighbour (NN) and next-nearest neighbour (NNN) couplings J 1 > 0, J 2 > 0 have been investigated experimentally for years [8][9][10][11] This class of systems has been recently expanded by several magnetic materials with a ferromagnetic (FM) NN coupling J 1 < 0 and a frustrating AFM NNN coupling J 2 > 0, e.g., Pb 2 VO(PO 4 ) 2 [12][13][14][15], (CuCl)LaNb 2 O 7 [16], SrZnVO(PO 4 ) 2 [15,17,18], and BaCdVO(PO 4 ) 2 [14,17,19]. The frustrating J 2 is believed to be large enough to drive these materials out of the FM phase.…”