Deformed spin-1/2 square lattice in antiferromagnetic NaZnVOPO4(HPO4)

We report the structural and magnetic properties of a new spin-1/2 antiferromagnet NaZnVOPO4(HPO4) studied via x-ray diffraction, magnetic susceptibility, high-field magnetization, specific heat, and P-31 nuclear magnetic resonance (NMR) measurements, as well as density-functional band-structure calculations. While thermodynamic properties of this compound are well described by the J(1)-J(2) square-lattice model, ab initio calculations suggest a significant deformation of the spin lattice. From fits to the magnetic susceptibility we determine the averaged nearest-neighbor and second-neighbor exchange couplings of J(1) similar or equal to -1.3K and J(2) similar or equal to 5.6K, respectively, resulting in the effective frustration ratio alpha = J(2)/J(1) similar or equal to -4.3 that implies columnar antiferromagnetic order as the ground state. Experimental saturation field of 15.3 T is consistent with these estimates if 20% spatial anisotropy in J(1) is taken into account. Specific heat data signal the onset of a magnetic long-range order at T-N similar or equal to 2.1K, which is further supported by a sharp peak in the NMR spin-lattice relaxation rate. The NMR spectra mark the superposition of two P lines due to two nonequivalent P sites where the broad line with the strong hyperfine coupling and short T-1 is identified as the P(1) site located within the magnetic planes, while the narrow line with the weak hyperfine coupling and long T-1 is designated as the P(2) site located between the planes.

Automated summary

The structural and magnetic properties of a new spin-1/2 antiferromagnet NaZnVOPO4(HPO4) were studied using various methods, revealing significant magnetic behaviors and characteristics. The findings suggest that this compound exhibits unique features that deviate from conventional models.