Charge Ordering and Magnetic Exchange in the Ladder-Type Compound NH${}_4$V${}_2$O${}_5$

Abstract

The low-temperature electronic and magnetic properties of NH${}_4$V${}_2$O${}_5$, an isoelectronic analog of the spin-ladder compound ${\alpha }^{\prime }$-NaV${}_2$O${}_5$, are investigated using DFT+$U$ calculations. Two charge-ordering patterns - zigzag and linear chains of V${}^{4+}$/V${}^{5+}$ ions - are considered. The zigzag configuration is found to be energetically preferred and exhibits insulating behavior with a band gap of 1.7 eV. In this state, magnetic V${}^{4+}$ (d${}^1$) ions form antiferromagnetically coupled spin chains. Calculated exchange interactions reveal strong diagonal (intrarung) and interladder couplings, indicating a complex spin-ladder network. These results suggest that NH${}_4$V${}_2$O${}_5$ retains essential spin-ladder characteristics while displaying new structural and magnetic features arising from the larger size and non-spherical geometry of the NH${}_4^{+}$ ion compared to Na${}^{+}$.