| Residential College | false |
| Status | 已發表Published |
| Title | SYNTHESIS AND STRUCTURAL AND PHYSICAL PROPERTIES OF FUNCTIONAL MAGNETIC MATERIALS |
| Author | Qian Zhao, Haifeng Li 
|
| Subtype | 博士Phd |
| Thesis Advisor | LI HAIFENG |
| Date Issued | 2024-08 |
| Degree Grantor | University of Macau |
| Place of Conferral | Macau |
| Degree Name | Ph.D. |
| Abstract | The feld of functional magnetic materials is a burgeoning area of research with profound implications for technology and science. These materials, characterized by their unique magnetic properties, are pivotal in the advancement of various applications. Research into functional magnetic materials encapsulates the synthesis and manipulation of compounds to unveil new phenomena and harness their potential for innovative applications. This endeavor is underscored by the ongoing quest to understand the complex interplay between magnetic properties and material structure at the atomic level. As researchers unravel these relationships, the insights gained pave the way for the design of materials with tailored magnetic behaviors, opening new frontiers in technology development. In this thesis, single crystals of YCrO3 were grown using the floating-zone method, and their structural properties from 36 K to 300 K were investigated through variabletemperature X-ray diffraction, revealing no structural phase transitions induced by temperature changes. The antiferromagnetic transition temperature (TN) of YCrO3 was determined to be 141.58(5) K through magnetization measurements using PPMS, where weak ferromagnetism was observed below TN. Anisotropic magnetostriction in lattice constants a, b, and c was discovered via Rietveld refnement of the variabletemperature X-ray diffraction data, along with a study of the crystal’s local distortions. To address the relationship between ferroelectricity and structural symmetry in YCrO3, synchrotron X-ray diffraction was performed at 120 K, 300 K, and 500 K. For the frst time, both P1211 and traditional Pmnb space groups were utilized to refne the synchrotron radiation data of YCrO3, examining bond lengths, angles, and local structural distortions. PDF analysis of the synchrotron data revealed that the local structure of YCrO3 above the ferroelectric transition temperature tends towards a non-centrosymmetric P1211 space group. Furthermore, polycrystalline samples of the ferromagnetic semiconductor EuAgP were successfully synthesized, and a systematic study of its structural, magnetic, specifc heat, band gap, and magnetoresistance properties was conducted. The ferromagnetic transition temperature (TC) of EuAgP was determined to be 16.45(1) K. The semiconductor characteristics were uncovered through differential scanning calorimetry, suggesting EuAgP might be an intrinsic semiconductor, further validated by re sistivity measurements. A notable magnetoresistance of up to -30.73% was observed, inspiring potential applications for EuAgP. The band gap was calculated to be approximately 1.324 eV, and XPS analysis indicated potential valence fluctuations in EuAgP. Lastly, non-magnetic Sr2+ doping on EuAgP was explored, and a detailed investigation of the structural, magnetic, specifc heat, and magnetoresistance properties of the series with varying doping concentrations was conducted. Sr2+ doping sup pressed the paramagnetic-ferromagnetic transition and shifted the dominant contribution near the transition temperature from magnons to electrons and phonons. It also enhanced the magnetoresistance performance of EuAgP from approximately -30% to about -60%, providing a means to control the magnitude and sign of magnetoresistance through doping. |
| Subject Area | 材料科学 |
| Language | 英語English |
| Document Type | Thesis |
| Collection | INSTITUTE OF APPLIED PHYSICS AND MATERIALS ENGINEERING |
| Corresponding Author | Qian Zhao, Haifeng Li |
| Recommended Citation GB/T 7714 | Qian Zhao, Haifeng Li. SYNTHESIS AND STRUCTURAL AND PHYSICAL PROPERTIES OF FUNCTIONAL MAGNETIC MATERIALS[D]. Macau, University of Macau, 2024. |
| Files in This Item: | Download All | |||||
| File Name/Size | Publications | Version | Access | License | ||
| thesis.pdf（24883KB） | 学位论文 | 开放获取 | CC BY-NC-SA | View Download | ||
Items in the repository are protected by copyright, with all rights reserved, unless otherwise indicated.
Edit Comment