Hao Liu

Bio: Hao Liu is an academic researcher from Ministry of Industry and Information Technology of the People's Republic of China. The author has contributed to research in topics: Phase transition & Thin film. The author has an hindex of 1, co-authored 3 publications receiving 3 citations. Previous affiliations of Hao Liu include Nanjing University of Aeronautics and Astronautics.

Critical behavior in hexagonal Y2Fe17: magnetic interaction crossover from 3D to 2D Ising model

Abstract: The critical behavior of single phase Y2Fe17 melt-spun ribbons with the Th2Fe17-type crystal structure has been studied around the transition temperature (TC). This alloy undergoes a second-order ferromagnetic (FM)–paramagnetic (PM) phase transition at TC = 301 K. Various techniques, such as the modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis, were used to determine the critical exponents that were found to be β = 0.226(3), γ = 1.296(2), and δ = 6.804(5). The universality class of the critical phenomenon in the Y2Fe17 ribbons can be explained with the help of the renormalization group theory approach, in which the magnetic properties show a feature changing from three (3D)- to two-dimensional (2D) Ising model. The first-principles calculations based on density functional theory qualitatively explain the experimental results, confirming the strong correlation between lattice atoms and critical behavior in magnetic intermetallic Y2Fe17.

Universality class change from Mean-Field to 3D-Heisenberg in magnetocaloric compounds <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si60.svg"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">SmNi</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn><mml:mo>-</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si61.svg"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Fe</mml:mi…

Abstract: We report a study of universality class change from Mean-Field to 3D-Heisenberg in magnetocaloric compounds SmNi3-xFex. Three conventional techniques are used to identify the universal classes: the Modified Arrott plot, Kouvel-Fisher plot, and critical isotherm technique. The calculated critical exponents were confirmed and the isotherm M(H) curves in paramagnetic state and ferromagnetic state fall in two separated universal branches. The exponents found are similar to those determined from the renormalization group approach for a heuristic mean-field (d=3,n=3) and 3D-Heisenberg (d=3,n=3) model for SmNi3 and SmNi2.2Fe0.8, respectively.

Mechanically Modulated Ferromagnetism and Critical Properties of Flexible Perovskite SrRuO3 Thin Film

Abstract: In an effort to explore new electronic devices with multiple functionalities, there are numerous studies of depositing perovskite oxides on flexible substrates to replace rigid silicon‐based wafer in device applications. In this study, the growth of pseudocubic SrRuO 3 single‐crystal thin film on a transparent and flexible muscovite is established. The experimental results confirm that the Curie temperature T C and the magnetic properties can be effectively tuned via the mechanical strain due to the facilitation of flexible substrate. It is found that the tensile strain increases while the compressive strain decreases the spontaneous magnetization for the thin film suffering the same ±0.24% strain. Based on the study of critical behavior, the critical exponents β = 0.543(19) and γ = 1.262(1) with the critical temperature T C = 159.04(5) K and T C = 159.10 K, respectively, are obtained by the modified Arrott plot. The set of critical exponents matches well with Widom scaling relation and the scaling equation, indicating these critical exponents are intrinsic for SrRuO3 thin films. Moreover, it is achieved that the SrRuO3 thin films exhibit a long‐range interaction coupled with 3D‐Heisenberg type.

Tunable Ferromagnetism in LaCoO3 Epitaxial Thin Films

Abstract: Ferromagnetic insulators play a crucial role in the development of low‐dissipation quantum magnetic devices for spintronics. Epitaxial LaCoO3 thin film is a prominent ferromagnetic insulator, in which the robust ferromagnetic ordering emerges owing to epitaxial strain. Whereas it is evident that strong spin‐lattice coupling induces ferromagnetism, the reported ferromagnetic properties of epitaxially strained LaCoO3 thin films are highly consistent. For example, even under largely modulated degree of strain, the reported Curie temperatures of epitaxially strained LaCoO3 thin films lie in a narrow range of 80–85 K, without much deviation. In this study, substantial enhancement (≈18%) in the Curie temperature of epitaxial LaCoO3 thin films is demonstrated via crystallographic orientation dependence. By changing the crystallographic orientation of the films from (111) to (110), the crystal‐field energy is reduced and the charge transfer between the Co and O orbitals is enhanced. These modifications lead to a considerable enhancement of the ferromagnetic properties (including the Curie temperature and magnetization), despite the identical nominal degree of epitaxial strain. The findings of this study provide insights into facile tunability of ferromagnetic properties via structural symmetry control in LaCoO3.