S. L. Zuo

Negative thermal expansion and magnetocaloric effect in Mn-Co-Ge-In thin films

MnCoGe-based alloys with magnetostructural transition show giant negative thermal expansion (NTE) behavior and magnetocaloric effects (MCEs) and thus have attracted a lot of attention. However, the drawback of bad mechanical behavior in these alloys obstructs their practical applications. Here, we report the growth of Mn-Co-Ge-In films with thickness of about 45u2009nm on (001)-LaAlO3, (001)-SrTiO3, and (001)-Al2O3 substrates. The films grown completely overcome the breakable nature of the alloy and promote its multifunctional applications. The deposited films have a textured structure and retain first-order magnetostructural transition. NTE and MCE behaviors associated with the magnetostructural transition have been studied. The films exhibit a completely repeatable NTE around room temperature. NTE coefficient α can be continuously tuned from the ultra-low expansion (αu2009∼u2009−2.0u2009×u200910−7/K) to αu2009∼u2009−6.56u2009×u200910−6/K, depending on the growth and particle size of the films on different substrates. Moreover, the films e...

Complex magnetic properties and large magnetocaloric effects in RCoGe (R=Tb, Dy) compounds

Complicated magnetic phase transitions and Large magnetocaloric effects (MCEs) in RCoGe (R=Tb, Dy) compounds have been reported in this paper. Results show that the TbCoGe compounds have a magnetic phase transition from antiferromagnetic to paramagnetic (AFM-PM) at TN∼16 K, which is close to the value reported by neutron diffraction. The DyCoGe compound undergoes complicated phase changes from 2 K up to 300 K. The peak at 10 K displays a phase transition from antiferromagnetic to ferromagnetic (AFM-FM). In particular, a significant ferromagnetic to paramagnetic (FM-PM) phase transition was found at the temperature as high as 175 K and the cusp becomes more abrupt with the magnetic field increasing from 0.01 T to 0.1 T. The maximum value of magnetic entropy change of TbCoGe and DyCoGe compounds achieve 14.5 J/kg K and 11.5 J/kg K respectively for a field change of 0-5 T. Additionally, the correspondingly considerable refrigerant capacity value of 260 J/kg and 242 J/kg are also obtained respectively, sugges...

Zero-field skyrmions generated via premartensitic transition in Ni50Mn35.2In14.8 alloy

Magnetic phase transition contributes to magnetocaloric effects and magnetoelastic coupling, producing significant multifunctions in Ni-based Heusler alloys. In this paper, the peculiar intermediate premartensitic phase during the transition from parent phase to martensite is identified in Ga-free Ni50Mn35.2In14.8 alloy via Lorentz transmission electron microscopy combined with in situ magnetizing and cooling manipulation. The simultaneous coexistence of three skyrmion configurations at zero field in martensite is directly observed with correlation to the appearance of the intermediate magnetic phase and martensite twinning confinement. The evolution of magnetic domains demonstrates a mechanism to generate skyrmions with magnetization orientation adjusted via magnetic phase transition, which illustrates the associated physical properties.

Composition design for (PrNd–La–Ce)2Fe14B melt-spun magnets by machine learning technique

Data-driven technique is a powerful and efficient tool for guiding materials design, which could supply as an alternative to trial-and-error experiments. In order to accelerate composition design for low-cost rare-earth permanent magnets, an approach using composition to estimate coercivity (H cj) and maximum magnetic energy product ((BH)max) via machine learning has been applied to (PrNd–La–Ce)2Fe14B melt-spun magnets. A set of machine learning algorithms are employed to build property prediction models, in which the algorithm of Gradient Boosted Regression Trees is the best for predicting both H cj and (BH)max, with high accuracies of and 0.89, respectively. Using the best models, predicted datasets of or (BH)max in high-dimensional composition space can be constructed. Exploring these virtual datasets could provide efficient guidance for materials design, and facilitate the composition optimization of 2:14:1 structure melt-spun magnets. Combined with magnets cost performance, the candidate cost-effective magnets with targeted properties can also be accurately and rapidly identified. Such data analytics, which involves property prediction and composition design, is of great time-saving and economical significance for the development and application of LaCe-containing melt-spun magnets.

Direct observation of the magnetic domain evolution stimulated by temperature and magnetic field in PrMnGeSi alloy

The magnetic domain evolution behavior under external field stimuli of temperature and magnetic field in PrMn2Ge0.4Si1.6 compound is investigated using Lorentz transmission electron microscopy. A spontaneous 180° magnetic domain is observed at room temperature and it changes with temperature. Dynamic magnetization process is related to the rotation of magnetic moments, resulting in the transforming of magnetic domains from 180° type to a uniform ferromagnetic state with almost no pinning effects under the in-plane magnetic field at room temperature. X-ray powder diffraction is performed on PrMn2Ge0.4Si1.6 at different temperatures to study the temperature dependence of crystal structure and lattice parameter.

The magnetic properties of (La,Ce)Co5 ((La,Ce)=La0.35Ce0.65, La-Ce mischmetal) nanoflakes prepared by surfactant-assisted ball milling

The hard magnetic (La,Ce)Co5 nanoflakes with high coercivity and narrow thickness distribution have been successfully obtained by surfactant-assisted ball milling (SABM). The magnetic properties, morphology and interaction of (La,Ce)Co5 nanoflakes are studied in this work. The coercivity and remanence ratio of (La,Ce)Co5 nanoflakes are 5.48 kOe and 0.71, respectively. The X-ray powder diffraction (XRD) patterns indicate that the (La,Ce)Co5 nanoflakes are CaCu5-type hexagonal crystal structure. The average thickness and aspect ratio are 47 nm and 40, respectively. The intergrain interaction of the (La,Ce)Co5 nanoflakes is studied using the δm(H)-curves technique which shows the magnetostatic-dominated particle interaction. The high coercivity and narrow thickness distribution of (La,Ce)Co5 nanoflakes could be promising for the future development of the high performance soft/hard exchange spring magnets.

Magnetic properties and magnetocaloric effects of RNiSi2 (R= Gd, Dy, Ho, Er, Tm) compounds

Orthorhombic CeNiSi2-type polycrystalline RNiSi2 (R=Gd, Dy, Ho, Er, Tm) compounds were synthesized and the magnetic and magnetocaloric properties were investigated in detail. The transition temperatures of RNiSi2 compounds are all in a very low temperature range (<30 K). As temperature increases, all of the compounds undergo an AFM to PM transition (GdNiSi2 at 18 K, DyNiSi2 at 25 K, HoNiSi2 at 10.5 K, ErNiSi2 at 3 K and TmNiSi2 at 3.5 K, respectively). ErNiSi2 compound shows the largest (ΔSM)max (maximal magnetic entropy change) among these compounds. The value of (ΔSM)max is 27.9 J/kgK under a field change of 0-5 T, which indicates that ErNiSi2 compound is very competitive for practical applications in low-temperature magnetic refrigeration in the future. DyNiSi2 compound shows large inverse MCE (almost equals to the normal MCE) below the TN which results from metamagenitic transition under magnetic field. Considering of the normal and inverse MCE, DyNiSi2 compound also has potential applications in low-...

Influence of misch metal content on microstructure and magnetic properties of R–Fe–B magnets sintered by dual alloy method

MM14Fe79.9B6.1/Nd13.5Fe80.5B6 magnets were fabricated by dual alloy method (MM, misch metal). Some magnets have two Curie temperatures. Curie temperatures T-c1 corresponds to the main phase which contains more LaCe, and Tc1 decreases from 276.5 degrees C to 256.6 degrees C with the content of MM increasing from 30.3 at.% to 50.6 at.%. The variation of Br with the increase ofMMindicates the existence of inter-grain exchange coupling in the magnets. When MM/R = 7.11 kOe and the maximum energy product (BH)(max) >= 41 MGOe. Compared with Nd, La and Ce are easier to diffuse to the grain boundaries in the sintering process, and this will cause the decrease of H-cj. Due to the diffusion between the grains, the atomic ratio of La, Ce, Pr, and Nd in each grain is different and the percentage of Nd in all grains is higher than that in misch metal.