Multiferroic Quantum Criticality in a Proper Ferroelectric Quasi‐one‐dimensional Ising Antiferromagnet

ABSTRACT Quantum phase transitions are driven at absolute zero by quantum‐mechanical fluctuations, offering unique opportunities for the emergence of exotic phenomena ranging from unconventional superconductivity to quantum magnetism. In multiferroics, where magnetic and ferroelectric orders are cross‐correlated, this raises an intriguing possibility: a state of quantum criticality in which both fluctuations are intertwined. Here we show that the quasi‐one‐dimensional Ising antiferromagnet Sr 1− x Ba x Co 2 V 2 O 8 hosts multiferroic quantum criticality through the coexistence of ferroelectric and magnetic quantum critical points (QCPs) tuned by independent non‐thermal parameters. Structural and dielectric analyses establish this system as a proper displacive‐type ferroelectric—an exceptionally rare feature among magnetic materials. Isovalent Ba substitution continuously suppresses the ferroelectric transition to zero temperature, producing a quantum paraelectric state with a signature T 2 scaling of the inverse permittivity. In this regime, a transverse magnetic field drives the system to a magnetic QCP. Their resulting coexistence gives rise to a pronounced magnetocapacitance, revealing a strong interplay between fluctuations in the lattice and spin systems. Our findings establish Sr 1− x Ba x Co 2 V 2 O 8 as a unique platform for opening new avenues at the intersection of quantum criticality and multiferroicity.