- Master the technology of making multiferroics single-phase and multi-phase structural materials.
- Determination of electro-magnetic correlation on the basis of ferroelectric and ferromagnetic properties of multiferroics materials.

Theoretical results:
- Successfully fabricated BiFeO₃ materials system without doping and with Nd, La doping by high-energy ball milling method combined with heat treatment for 10 hours at 850oC in air. The obtained particles have a size of 100 nm. La or Nd doping in the sublattice of BFO contributes to the simultaneous improvement of the electrical and magnetic properties of the material. The helical spin structure of BFO is suppressed by the substitution of La3+ or Nd3+ ions for Bi3+ ions, leading to structural distortions that increase magnetization. The substitution of La3+ or Nd3+ only suppresses but cannot completely destroy the twisted spin structure and contributes to the continuous increase of the Fe-O-Fe bond angle. At the same time, the deformation of the FeO₆ octahedron improved the electrical polarization of the material in the external electric field. Corresponding to the doping concentration La is x = 0.2 and Nd is x = 0.3, the electromagnetic properties of the material are shown most clearly.
- Successfully fabricated the x(M,Fe)₃O₄/(1-x)BaTiO₃ composite material system (M is Fe, Co, Ni), with the size of about 50-100 nm. Changing the content of (M,Fe)₃O₄ in the sample did not significantly affect the particle size obtained. That means that the particle size of (M,Fe)₃O₄-BaTiO₃ depends only on the material fabrication technology parameters. + Successfully improved both ferroelectric and ferromagnetic properties for composite multiferroic materials (1-x)BaTiO₃/x(M,Fe)₃O₄. The main factors that can contribute to the improvement of the multiferroic properties of the material are the reduction of resistivity and the failure of the lattice.
Applied results:
- The 0.3NiFe₂O₄/0.7BaTiO₃ nanomaterials have the ability to lose color Rhoramine B. Calculate the processing saturation time of 140 min, the half-life of 27 min, and the treatment rate constant Ka = 0.02 min -1.
- The 0.3NiFe₂O4/0.7BaTiO₃ nanomaterials used as fillers in acrylic paints have the ability to effectively shield and absorb electromagnetic microwaves. The ability to absorb electromagnetic microwaves of the composite multiferroics material is over 99.9%, corresponding to the absorption peak frequency position of 16.8 GHz with an RL value of approximately -39.8 dB.

- Successfully fabricated single-phase multiferroic materials with undoped BiFeO3 structure and doped La, Nd by high-energy ball milling combined with heat treatment method.  With the increase of impurities La, Nd, the ferroelectric and ferromagnetic properties of the material system are improved markedly. Especially for Bi1-xLaxFeO₃ (x = 0, 0.1; 0.2; 0.3) material with hexagonal structure has been successfully fabricated. Especially when La is doped, the values of residual polarization (P_r), and residual magnetization (M_r) gradually increase and reach the maximum value corresponding to La-doped concentration of x = 0.2. Besides, the bandgap energy (E_g) value of the material also gradually decreased and reached the minimum value of 1.75 eV corresponding to this doping concentration. With the optical band gap in the visible region, La-doped BiFeO₃ material is a potential material for optoelectronic devices and solar cell applications.
- Successfully carried out research on fabrication and properties of composite multiferroics materials (1-x)BaTiO₃/x(M, Fe)₃O₄ nanostructure by high-energy ball milling combined with heat treatment method. The ferroelectric (FE) and ferromagnetic (FM) properties of the composites were significantly improved with the gradual increase of the ferromagnetic content. The values of H_c, M_r, M_s, P_m, P_r, and the WLE loss energy density increase as the ferromagnetic phase concentration increases.
- Successfully tested the photocatalytic ability of composite multiferroics materials by Rhoramine B treatment, with treatment saturation time of 140 min, a half-life of 27 min and treatment rate constant Ka = 0.02 min-1.
- Research and test successfully the ability to absorb electromagnetic microwaves of the composite multiferroics material reaches over 99.9%, corresponding to the position of the absorption peak frequency of 16.8 GHz with an RL value of approximately -39.8 dB.

- Scientific papers in referred journals (list):
+ Dao Son Lam, Nguyen Ngoc Tung, Dang Duc Dung, Bui Xuan Khuyen, Vu Dinh Lam and Tran Dang Thanh,”Electrical, magnetic and microwave absorption properties of multiferroic NiFe2O4-BaTiO3 nanocomposites”, Mater. Res. Express 9 (2022) 075004, https://doi.org/10.1088/2053-1591/ac7fe1.
+ Son Lam Dao, Chi Linh Dinh, Ngoc Bach Ta, Duc Dung Dang, Thu Huong Ngo, Dang Thanh Tran, “Effect of la on the structure and characteristics of multiferroic BiFeO3”. Accepted in Vietnam Journal of Science and Technology (VAST 2)
+ Conference proceedings: Dao Son Lam, Dang Duc Dung, Nguyen Huy Dan, Ta Ngoc Bach, Dinh Chi Linh, Ngo Thu Huong, Tran Dang Thanh, “Improvement of electrical and magnetic properties of composite nanomaterial multiferroics CoFe2O4/BaTiO3, SPMS Conference 2021 (Accepted for publication in the Proceedings).
+ Support training: 01 Master.
+ Has been assigned to the Institute of Materials Science, Vietnam Academy of Science and Technology in December 2020 (with proof of recruitment decision).