Date of Graduation

5-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics (PhD)

Degree Level

Graduate

Department

Physics

Advisor/Mentor

Jin Hu

Committee Member

Hugh O. H. Churchill

Second Committee Member

Yong Wang

Keywords

low-dimensional magnetism, magnetic properties, tunable magnetism

Abstract

The recently discovered two-dimensional (2D) magnetism has attracted intensive attention due to possible magnetic phenomenon arising from 2D magnetism and their promising potential for spintronics applications. The advances in 2D magnetism have motivated the study of layered magnetic materials, and further enhanced our ability to tune their magnetic properties. Among various layered magnets, tunable magnetism has been widely investigated in metal thiophosphates MPX3. It is a class of magnetic van der Waals (vdW) materials with antiferromagnetic ordering persisting down to atomically thin limit. Their magnetism originates from the localized moments due to 3d electrons in transition metal ions. So, their magnetic properties are strongly dependent on the choice of M. With this motivation, we synthesized metal-substituted MPX3 compounds such as Ni1-xMnxPS3 (0 ≤ x ≤ 1), Ni1-xCrxPS3 (0 ≤ x ≤ 0.09), and Fe1-xMnxPSe3 (0 ≤ x ≤ 1). The magnetic properties have been found to be very tunable with metal substitutions. Furthermore, we performed previously unexplored non-magnetic X substitution in MnPS3-xSex (0 ≤ x ≤ 3), FePS3-xSex (0 ≤ x ≤ 3), and NiPS3-xSex (0 ≤ x ≤ 1.3). Interestingly, such non-magnetic S-Se substitution also effectively modifies the magnetic exchange and anisotropy in MPX3¬. In addition to M and X substitutions, we conducted electrochemical intercalation of Li into NiPS3. We found the emergence of ferrimagnetism at low temperature in Li-intercalated NiPS3, which has never been observed due to substitution technique. Such efficient engineering of magnetism provides a suitable platform to understand low-dimensional magnetism and design future magnetic devices.

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