1. Full name: Nguyen Thi My Duc                                   2. Sex: Female

3. Date of birth: April 28, 1984                                        4. Place of birth: Thua Thien - Hue Province

5. Admission decision number: Decision No. 4860/QĐ-ĐHKHTN, dated on  24/11/2014 by Rector of VNU University of Science.

6. Changes in academic process:

- Decision No. 4067/QĐ-ĐHKHTN, dated on 01/12/2016 on adjusting the supervisor of the doctoral thesis.

- Decision No. 596/QĐ-ĐHKHTN, dated on 06/03/2018 on time extension of the research training course and the thesis defense for the PhD. student.

- Decision No. 4728/QĐ-ĐHKHTN, dated on 28/12/2018 on time extension of the research  training course and the thesis defense for the PhD. student.

7. Official thesis title: Exploring the magnetocaloric effects in perovskite manganite and Gd-containing alloy microwires

8. Major: Solid State Physics                                         9. Code: 9440130.02

10. Supervisors: Assoc.Prof.Dr. Ngo Thu Huong; Prof.Dr. Phan Manh Huong

11. Summary of the new findings of the thesis:

We have successfully fabricated perovskite samples REMnO­3 (RE = La, Pr) and (La0.5Pr0.5)1-x­BaxMnO3 with x = 0-0.5. The structural and magnetic properties of the samples were systematically characterized, showing the optimal magnetic property for the x = 0.4 composition. 

w The magnetocaloric effect and critical behavior of LPBMO were studied. A detailed analysis of the critical exponents indicates a long-range ferromagnetic interaction below TC but a short-range interaction above TC, causing the ferromagnetic-paramagnetic (FM–PM) phase transition to broaden and consequently enhancing the relative cooling power (RCP). Although perovskite manganites are cost-effective and easy to be fabricated, their MCE characteristics do not fulfil the requirements of an active magnetic refrigerator (AMR).

w Having studied the structural, magnetic properties, magnetocaloric effect, and unusual critical behavior of the melt-extracted amorphous Gd60Fe20Al20 microwires, we have achieved the larger RCP values of these microwires as compared to GdFeAl alloys or ribbons or even Gd60Co20Al20 microwires. The coexistence of ferromagnetic (Gd-Gd, Fe-Fe) and antiferromagnetic (Gd-Fe) interactions resulted in the broadened FM-PM transition and hence the enhanced RCP.

w We have systematically investigated the structural, magnetic properties, magnetocaloric effect, and critical exponents of melt-extracted amorphous Gd50(Co69.25Fe4.25Si13B13.5)50 microwires. The combination of a soft ferromagnetic Co69.25Fe4.25Si13B13.5 alloy component with Gd creates a novel class of magnetocaloric microwires possessing a higher TC than that of Gd-Co-Al microwires while retaining a large RCP. The obtained critical exponents of the Gd50(Co69.25Fe4.25Si13B13.5)50 microwires are close to those of systems exhibiting long-range ferromagnetic interactions below TC and short-range interactions above TC, similar to LPBMO.

w We have designed and characterized the structural, magnetic properties, and magnetocaloric effect of melt-extracted Gd73.5Si13B13.5/GdB6 microwires, with GdB6 nanocrystals (~10 nm) embedded in an amorphous Gd73.5Si13B13.5 matrix. The large MCE and RCP make these composite microwires a very attractive candidate for active magnetic cooling applications.

The research results of this thesis have been published in 4 articles of ISI journals (1 paper in Intermetallics (ISI, Q1), 2 papers in Journal of Alloys and Compounds (ISI, Q1), and 1 paper in Journal of Electronic Materials (ISI, Q2)); 2 papers in domestic journals and 6 reports and abstracts in national and international symposiums.

12. Pratical applicability, if any:

The designed Gd-based alloy microwires are highly applicable in advanced magnetic cooling devices, owing to their outstanding magnetic and magnetocaloric properties. Creating the composite microwires with weak antiferromagnetic nanocrystals embedded in an amorphous ferromagnetic matrix represents a novel approach for enhancing the magnetocaloric effect of magnetic alloy microwires.

13. Future research directions, if any

Investigations into the magnetocaloric effect of alloy microwires with different components that possess various Curie temperatures for magnetic refrigeration application at different temperature regions. Designs of new magnetic beds composed of MCE wire arrays and laminate structures would also be an interesting approach.

14. Thesis-related publications:

[1] N.T.M.Duc, C.M.Hung, N.T.Huong, and M.H.Phan, “Magnetic interactions and magnetocaloric effect in (La0.5Pr0.5)0.6Ba0.4MnO3: Effect of A-site co-doping”, Journal of Electronic Materials 49 (2020), pp 2596-2607 (ISI, Q2)

[2] N.T.M.Duc, H.X. Shen, O. Thiabgoh, N.T.Huong, J.F.Sun, and M.H.Phan, “Melt-extracted Gd73.5Si13B13.5/GdB6 ferromagnetic/antiferromagnetic microwires with excellent magnetocaloric properties”, Journal of Alloys and Compounds, 818 (2020), 153333 (ISI, Q1)

[3] N.T.M.Duc, H.X.Shen, E.Clements, O.Thiabgoh, J.L.Sanchez Llamazares, C.F.Sanchez-Valdes, N.T.Huong, J.F.Sun, H.Srikanth, and M.H.Phan, “Enhanced refrigerant capacity and Curie temperature of amorphous Gd60Fe20Al20 microwires”, Journal of Alloys and Compounds 807 (2019), 151694 (ISI, Q1)

[4] N.T.M.Duc, H.X.Shen, E.Clements, O.Thiabgoh, J.L.Sanchez Llamazares, C.F.Sanchez-Valdes, N.T.Huong, J.F.Sun, H.Srikanth, and M.H.Phan, “Critical magnetic and magnetocaloric behavior of amorphous melt-extracted Gd50(Co69.25Fe4.25Si13B13.5)50 microwires”, Intermetallics 110 (2019), 106479 (ISI, Q1)

[5] Nguyen Thi My Duc, Ngo Thu Huong, Phan Manh Huong, The influence of ferromagnetic metal on Curie temperature TC of Gd-based magnetocaloric microwires, Solid State Physics and Material Science Conference ‘s proceedings SPMS - 2019 (Quynhon, Vietnam), pages 98 – 102

[6] N.T.M.Duc, M.Kurisu, K.Konishi, M.H.Phan, N.T.Huong, “Structure and magnetic properties of REMnO3 system”, VNU Journal of Science: Mathematics – Physics, Vol. 32, No. 4 (2016), pages 6-11

[7] Nguyen Thi My Duc, Ngo Thu Huong, Research the influence of rare earth ion on structural and magnetic properties of maganite perovskite, Journal of Science and Education, University of Science and Education, The University of Danang, No. 20(03) (2016) pages 1-6

[8] Nguyen Thi My Duc, Ngo Thu Huong, Structural and magnetic properties of (La0,5Pr0,5)1-xBaxMnO3 perovskite maganite (x = 0; 0.2 and 0.4), Proceedings on National Conference for Young Scientist in Pedagogical Universities 2016 (Hochiminh city, Vietnam), pages 905-914

[9] N.T.M.Duc, H.X.Shen, E.Clements, N.T.Huong, H.Srikanth, and M.H.Phan, “Magnetocaloric microwires for energy efficiency magnetics refrigeration”, Hanoi International Symposium on Advanced Materials and Devices (HISAMD 2019), January 10-12, 2019, Hanoi, Vietnam

[10] N.T.M.Duc, H.X.Shen, S.Jiang, N.T.Huong, J.F.Sun, and M.H.Phan, “Magnetic and Magnetocaloric Behaviors in Gd50Al25Co25/FeNi Core/Shell Structured Microwires”, The 5th International Conference of Asian Union of Magnetics Societies (IcAUMS 2018), June 3-7, 2018, Jeju, Korea

[11] N.T.M.Duc, N.T.Huong­­, M.H.Phan, “The effect of Ba doping on the structure and magnetic properties of the (La0.5,Pr0.5)1-xBaxMnO3 system (x=0;0.1;0.2;0.3;0.4;0.5)”, International Workshop on Advanced Materials and Nanotechnology (IWAMN 2016), November 3-5, 2016, Hanoi, Vietnam

[12] N.T.M.Duc, N.T.K.Van, N.T.Huong, M.Kurisu, K. Konishi and N.H.Hong, “Structure and magnetic properties of the RMnO3 system”, The International Workshop on Nanoscience and Nanotechnology: Opportunities for Academia & High Tech Industry, Joint 4th Asia-Pacific Chemical and Biological Microfluidics Conferences (IWNN-APCBM 2015), November 2-4, 2015, Danang, Vietnam