Spin disorder state in a site-depleted 3D coupled trillium spin-lattice system Pb1.5Fe2(PO4)3

• Published in: Journal of magnetism and magnetic materials Vol. 629; p. 173302
• Main Authors: Boya, K., Sahu, V.K., Kumar, R., Paulose, P.L., Koteswararao, B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2025
• Subjects: Competing magnetic interactions; Frustrated magnet; Spin disorder; Spin liquid behavior; Trillium lattice; Spin disorder; Spin liquid behavior; Trillium lattice; Frustrated magnet; Competing magnetic interactions
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2025.173302

The study of spin liquids has emerged as a prominent subject of investigation in the field of magnetism owing to their notable characteristics encompassing long-range entanglement, fractional excitations, and topological order. The spin-liquid state is an exotic state of matter with no conventional magnetic long-range order and is rarely observed in S = 52 systems. Here, we have studied the magnetic behavior of Pb1.5Fe2(PO4)3 (PbFPO) through magnetic and heat capacity measurements on polycrystalline samples. The PbFPO compound has two Pb sites with 25% site depletion in the lattice structure. The compound holds two trillium lattices of S = 52 moments in the unit cell, which are connected with additional magnetic couplings similar to that of KSrFe2(PO4)3. Despite the comparatively large Curie–Weiss temperature of -68 K (antiferromagnetic), the magnetic susceptibility data shows no sign of magnetic long-range order down to 2 K. The absence of field-dependent behavior in the heat capacity data up to 110 kOe field indicates that the PbFPO system possesses elevated spin correlations. The magnetic heat capacity data follows the power law behavior, probably stemming from the system’s gapless excitations from the spin-disordered state. Although the compound has a heavy site depletion, the spin disorder state is quite robust and is not even affected by the large magnetic fields. •Pb1.5Fe2(PO4)3 has a frustrated 3D network of coupled trillium spin lattice of S=52 moments.•The compound has 25% site depletion as compared to the Langbeinite structure like KSrFe2(PO4)3.•Despite of θCW of -68 K, long range order down to 2 K is not developed.•No field behavior in the Cm(T) until 110 kOe, implying that the AFM spin correlations are robust.•The system remains in disordered state despite 25% site depletion.