Author ORCID Identifier:

https://orcid.org/0009-0008-3161-3156

Date of Graduation

7-2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Hu, Jin

Committee Member

Nakamura, Hiro

Second Committee Member

Churchhill, Hugh O.H.

Keywords

Ferromagnetism, van der Waais Antiferromagnets, crystals, magnetism

Abstract

Recent discoveries of magnetism in low dimensions not only have gained fundamental scientific interest but also holds significant potential in numerous technological applications, such as spintronics. This has led to a wide range of efforts in the synthesis of new layered materials or tuning their existing magnetic properties, which has been instrumental in understanding the novel physical concept and development of new technological frontiers. Transition metal thiophosphate, MPS3, is a class of layered antiferromagnet family. The rich magnetic/crystal structure with delicate choice of transition metal (M) together with intriguing optical, electronic, and ferroelectric properties have placed them as a model system to study magnetism and relevant phenomena. Despite this, their antiferromagnetic ground state has restricted the detection and coupling of magnetism with its existing properties. Hence, realizing ferromagnetism is highly desirable although extremely demanding. With this motivation, we grew the single crystals of FePS3 and performed lithium intercalation using electrochemical setup. This resulted in the strong tuning of magnetism with low temperature ferromagnetic signature attributed to the spin-glass state. Furthermore, we grew the medium- entropy CuxNi2(1-x)CrxP2S6 (0 ≤ x ≤ 1) alloy and studied their structural and magnetic properties. We found that (Cu+Cr) co-substitution of Ni in Ni2P2S6 systematically leads to the evolution of crystal structure together with the strong tuning of magnetism. Additionally, stable ferromagnetism has been observed at lower temperatures in the intermediate compositions. In addition to the intercalation and medium-entropy alloying, we grow the Fe1-xCoxPS3 (0 ≤ x ≤ 0.78), Ni1-xFexPS3(0 ≤ x ≤ 1), and Ni1-xCoxPS3(0 ≤ x ≤ 0.83) single crystals and studied their magnetic properties. We found that the mixing of two highly anisotropic Fe2+ and Co2+ metal ions established well-defined ferromagnetism in specific compositions, which has not been achieved through metal substitution.

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