Magnetic Anisotropy-Controlled Exchange Bias and Related Spin Phenomena in Mn3- xCoxGa/Mn3Ga Bilayers
- 주제(키워드) Exchange bias effect , Magnetic anisotropy , Magnetic phase transition , Interfacial spin , Heusler compound
- 발행기관 서강대학교 일반대학원
- 지도교수 정명화
- 발행년도 2026
- 학위수여년월 2026. 8
- 학위명 박사
- 학과 및 전공 일반대학원 물리학과
- 실제URI http://www.dcollection.net/handler/sogang/000000083303
- UCI I804:11029-000000083303
- 본문언어 영어
- 저작권 논문은 저작권에 의해 보호받습니다.
초록(요약문)
In this study, Mn3-xCoxGa/Mn3Ga bilayers, composed of ferrimagnetic Mn3-xCoxGa and antiferromagnetic Mn3Ga, are investigated to understand how tunable magnetic anisotropy governs exchange bias （EB） and related spin phenomena. The EB effect plays an important role in spintronic devices and is determined by the interfacial spin configuration, but its underlying mechanism is still not fully understood. While longitudinal exchange bias （LEB） has been widely studied, perpendicular exchange bias （PEB） remains relatively less explored. Therefore, a comparative study of LEB and PEB within a same material family is essential for clarifying the role of magnetic anisotropy and interfacial spin alignment in the EB effect. Co substitution in Mn3-xCoxGa drives a structural and magnetic transition from a tetragonal phase with perpendicular magnetic anisotropy （PMA） to a cubic phase with in-plane magnetic anisotropy （IMA）, enabling systematic comparisons of LEB and PEB in Mn3-xCoxGa/Mn3Ga bilayers. The tetragonal-dominant （x = 0.12） and cubic- dominant （x = 0.57） samples exhibit anisotropy-dependent EB behavior, where the relative magnitudes of the EB field in the LEB and PEB configurations are governed by the easy- axis direction of the ferrimagnetic layer. Near the critical composition range around x ≈ 0.5, however, the EB behavior is strongly modified by competing PMA and IMA tendencies. In the critical regime, the EB effect is strongly enhanced, which is closely related to the reduced magnetization and frustrated interfacial antiferromagnetic spins near the critical composition. Furthermore, FC-dependent Hall anomalies resembling a topological Hall effect are observed in the critical-regime bilayers, suggesting coupling between the exchange-biased interfacial spin state and a non-collinear spin configuration. Overall, this work provides critical insights into the role of magnetic anisotropy and interfacial spin configuration in the EB effect, advancing the understanding of EB mechanisms in magnetic multilayers.
more목차
1. Introduction 1
2. Theory 5
2.1 Exchange bias 5
2.1.1 Conventional exchange bias 5
2.1.2 Uncompensated spins and surplus magnetization 8
2.1.3 Koon’s model and orthogonal spin configuration 9
2.1.4 Training effect of exchange bias 12
2.2 Magnetic anisotropy 14
2.3 Mn-based Heusler alloys 15
2.3.1 Heusler structure and magnetism 15
2.3.2 Tetragonal Mn3Ga and Co substitution 16
2.4 Hall effect 17
2.4.1 Anomalous Hall effect 18
2.4.2 Topological Hall effect 19
3. Experimental Details 20
4. Results and Discussion 22
4.1 Magnetic anisotropy-dependent exchange bias effect 22
4.1.1 Crystal structure characterization 22
4.1.2 Magnetic properties 25
4.1.3 Exchange bias effect 27
4.1.4 Field-cooling dependence of exchange bias 30
4.1.5 Training effect of exchange bias 37
4.2 Exchange bias effect and Hall response near the critical composition 42
4.2.1 Crystal structure near the Magnetic phase transition 42
4.2.2 Magnetic properties in the critical regime 45
4.2.3 Exchange bias effect in the critical regime 48
4.2.4 Field-cooling dependence of exchange bias in the critical regime 51
4.2.5 Training effect of exchange bias in the critical regime 56
4.2.6 Exchange bias behavior associated with the Hall anomaly 61
5. Conclusion 66
5. References 68
