Title Page

Contents

SUMMARY 10

Chapter 1. Introduction 12

1.1. 2D magnetic van der Waals materials 12

1.2. Crystal structure and magnetic properties of MPS₃ 17

Chapter 2. Experimental Details 21

2.1. Crystal Synthesis 21

2.2. DC Magnetization and magnetic susceptibility 23

2.2.1. Working principle of SQUID-VSM 23

2.2.2. Measurement conditions 26

2.3. Raman spectroscopy 26

2.3.1. Classical mechanism of Raman scattering 28

2.3.2. Theory of magnetic Raman scattering 31

2.3.3. Experimental setup 33

Chapter 3. Results and Discussion 36

3.1. Previous works 36

3.2. Magnetic susceptibility 38

3.3. Magnetization 42

3.4. Phonon Raman spectra 44

3.5. Two-magnon Raman scattering 48

3.6. Conclusion 53

Chapter 4. Reference 55

국문 초록 63

Figure 1-1. Diverse research subjects that can be explored with 2D magnetic vdW materials, reprinted from Ref. [22]. 14

Figure 1-2. Crystal structure and atomic force microscope image of NiPS₃, reprinted from Ref. [14].... 18

Figure 2-1. Photos of Ni₁₋ₓFeₓPS₃ single crystal and two-zone furnace. Shiny black single crystals of (a) NiFePS₃ (b) Ni₀.₅Fe₀.₅PS₃ (c) FePS₃. Samples were cut... 22

Figure 2-2. Sketch of a conventional vibrating sample magnetometer. 23

Figure 2-3. Magnetic properties measurement system (MPMS) and schematic of a SQUID.... 25

Figure 2-4. Energy diagram of the elastic (Rayleigh) and inelastic (Raman) scattering. Ground State (GS), Vibrational Excited state (VE), Virtual State (VS), Electronic... 27

Figure 2-5. Two-magnon excitation by Raman scattering in a square lattice antiferromagnet.... 32

Figure 2-6. Schematic diagram of Raman scattering measurements and experimental setup.... 34

Figure 3-1. Temperature dependent magnetic susceptibilities of Ni₁₋ₓFeₓPS₃ measured under external field of 1 T.... 39

Figure 3-2. First order temperature derivative of magnetic susceptibility and magnetic anisotropy.... 41

Figure 3-3. Magnetization of Ni₁₋ₓFeₓPS₃ measured at 2 K. M(H) measured with applied magnetic field (a) perpendicular and (b) parallel to the ab-plane. 43

Figure 3-4. Composition dependent Raman spectra of Ni₁₋ₓFeₓPS₃ in paramagnetic and antiferromagnetic phase.... 44

Figure 3-5. Composition dependence of phonon frequencies obtained by fitting raw data at 10 K. 46

Figure 3-6. Normalized intensity vs temperature plot of the symmetry-forbidden Ag mode. Spin-dependent Raman scattering occurs in the shaded temperature range and...[이미지참조] 47

Figure 3-7. Thermal evolution of magnetic Raman scattering response of Ni₁₋ₓFeₓPS₃. (a)-(e) Temperature dependent Raman spectra of Ni₁₋ₓFeₓPS₃ measured in cross... 49

Figure 3-8. Thermal renormalization of magnon energy and characteristic temperatures T*, TN*....[이미지참조] 51