Extrinsic negative magnetization and exchange bias of FePS₃(CoCp₂)_0.40

Van der Waals (vdW) crystals, particularly transition metal phosphorus trisulfides (MPX₃), have garnered significant attention because of their tunable magnetic properties through intercalation. This study investigated the magnetic behavior of FePS₃ intercalated with cobaltecene ions (FePS₃(CoCp₂)_0.40), focusing on its negative magnetization (NM) and exchange bias (EB) effects. Structural analysis reveals an expansion of the interlayer spacing from 6.46 Å to 11.95 Å and the emergence of spontaneous magnetization below 65 K. A robust NM is observed below ~35 K under zero-field cooling (ZFC), even at high magnetic fields. Detailed investigations demonstrate that this ZFC-NM arises from a combination of a negative trapped field in the superconducting magnet and the material’s giant coercive force rather than an intrinsic magnetic mechanism. Furthermore, the apparent EB effect, often misinterpreted as intrinsic, is attributed to a secondary minor-loop effect rather than genuine EB. By systematically excluding external influences, the study confirms that FePS₃(CoCp₂)_0.40 has no intrinsic NM or EB. This work provides a critical methodology to distinguish extrinsic from intrinsic magnetic phenomena in high-coercivity materials, advancing the understanding of vdW magnetism and its applications in spintronic devices.