Quantum well-modulated transport and voltage-controlled magnetic anisotropy in Cr/Fe/MgO junctions at room temperature

Quantum well (QW) states in ultrathin Fe layers can strongly influence transport and magnetic anisotropy in magnetic tunnel junctions, yet their formation in Fe/MgO systems is complicated by interface roughness and lattice mismatch. We fabricate high-quality single-crystal Cr/Fe/MgO multilayers to enhance QW confinement and study their effect on tunnel magnetoresistance (TMR) and voltage-controlled magnetocrystalline anisotropy (VCMA) at room temperature. Conductance measurements reveal clear resonant peaks, confirming QW formation. The strong QW produces a notable bias shift of the TMR maximum and a non-linear modulation of perpendicular magnetic anisotropy, enabling sign-tunable VCMA. We further examine how an interfacial Ir layer modifies the QW behavior and coupling to transport and anisotropy.