2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/104283A new quantum spin model with frustration, the `Union Jack' model on the square lattice, is analyzed using spin-wave theory. For small values of the frustrating coupling $α$, the system is N{\' e}el ordered as usual, while for large $α$ the frustration is found to induce a canted phase. The possibility of an intermediate spin-liquid phase is discussed.11 pages, 9 figuresStrongly Correlated ElectronsStatistical Mechanicstext