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Low grade waste heat accounts for ~65% of total waste heat, but conventional waste heat recovery technology exhibits low conversion efficiency for low grade waste heat recovery. Hence, we designed a thermomagnetic generator for such applications. Unlike its usual role as the coil core or big magnetic yoke in previous works, here the magnetocaloric material acts as a switch that controls the magnetic circuit. This makes it not only have the advantage of flux reversal of the pretzel-like topology, but also present a simpler design, lower magnetic stray field, and higher performance by using less magnetocaloric material than preceding devices. The effects of key structural and system parameters were studied through a combination of experiments and finite element simulations. The optimized max power density PDmax produced by our device is significantly higher than those of other existing active thermomagnetic, thermo, and pyroelectric generators. Such high performance shows the effectiveness of our topology design of magnetic circuit with magnetocaloric switch. The utilization of waste heat is an important way of combining energy saving to emission reductions. Here, authors demonstrate a magnetocaloric material as a controlling switch in a thermomagnetic generator for waste heat recovery. [ABSTRACT FROM AUTHOR]

In this study, a homemade uniaxial strain pressure cell was designed to be directly used in the standard magnetometers whereby the magnetic properties of samples subjected to a uniaxial strain and magnetic field were characterized. Its feasibility has been demonstrated by the uniaxial strain control of the phase transition and magnetocaloric effect in Ni40Co10Mn40Sn10 (NCMS) alloys. With the assistance of a uniaxial strain of ~0.5%, the cooling temperature span of NCMS alloys is broadened by 2 K, and the refrigeration capacity under a 3 T magnetic field change increases from 246 to 277 J/kg. This research provides not only direct experimental assistance for the tuning of phase transition by the uniaxial strain but also possibilities for studying the coupled caloric effect in first-order phase transition materials under a combined uniaxial strain and magnetic field by the thermodynamic analysis. [ABSTRACT FROM AUTHOR]

'Magic-angled' structure currently attracts increasing attention from condensed matter physics due to its amazing performance in superconductivity of graphene. The similar pattern formation of nanoparticles will bring about novel physics in nanoscale that causes the next generation nanodevices. However, it remains a challenging task to acquire such patterns by self-assembly process. In this article, we reported a Moiré interference pattern formation of magnetic nanoparticles regulated by a rotational magnetic field. The colloidal concentration, the strength, and the frequency of magnetic field were found to affect the pattern formation. The mechanism lied in a two-step process. First, the magnetic nanoparticles formed bilayers of superlattice driven by hydrophobic interaction of interfacial self-assembly. Then, the bilayers of superlattice yielded asynchronous rotational displacement resulting from the magnetic force so that the Moiré interference pattern of nanoparticles formed. This fabrication methodology based on the field-controlled self-assembly provided a novel and simple means to get 'magic angled' structures in nanoscale that will enrich the physical understanding of nanotechnology. [ABSTRACT FROM AUTHOR]

The caloric effects under combined applications of magnetic field and hydrostatic pressure to a MnCoSi meta-magnet were investigated. Under a magnetic field change of 0–5 T, the maximum magnetic entropy change was enhanced by 35.7% when a 3.2kbar hydrostatic pressure was applied, and the cooling temperature span was extended by 60 K when a hydrostatic pressure of 9.7 kbar was applied. The coupled caloric entropy change, which originates from the coupling between the magnetism and volume, was calculated and accounted for the enhanced entropy change of MnCoSi. The present work facilitates the use of MnCoSi as a solid-state refrigerant and also enriches the investigation of the multicaloric effect under multiple external fields. [ABSTRACT FROM AUTHOR]

Two-dimensional electron gas (2DEG) has abundant properties, which motivate not only fundamental physical interest but also concepts for device designing. While most of the reported 2DEGs are based on SrTiO3, here we report on a systematic investigation on anatase TiO2-based 2DEG generated by ion irradiation. By irradiating the surface layer of the anatase TiO2 films with appropriate argon ion beams, we gained the 2DEGs with a thickness of 4 nm. Unique transport behaviours of a T−1/3 or ln(1/T) sheet resistance dependence below 100 K are observed depending on irradiation time. Unusually large positive MR is observed for which the magnetic field causes a strong shrinkage of electron wave functions, and fairly large negative MR is detected in the 2DEG, arising from the depression of magnetic scattering. [ABSTRACT FROM AUTHOR]

We investigated the martensitic transition and the magnetic properties of Mn1−xCoGe melt-spun ribbons. The as-prepared Mn1−xCoGe ribbons crystallize in austenite hexagonal phase with a textured structure. The postannealing process promotes the formation of the martensitic phase and homogenization of the alloy, resulting in a first-order magnetostructural transition in the annealed ribbons, and thus a giant magnetocaloric effect. The magnetic entropy change around the transition reaches 19 J/kgK for a magnetic field change of 0–5 T. Furthermore, it is found that the hysteresis loss around the magnetostructural transition is negligible in present annealed ribbons, which would facilitate the application of Mn1−xCoGe alloys. [ABSTRACT FROM AUTHOR]

The microstructure and magnetic properties for LaFe10.85 Co0.65Si1.5C0.2, LaFe11.5Si1.5C0.2 and LaFe10.85Co0.65Si1.5 compounds were investigated. The ingots were prepared by 5 kilogram Vacuum Induction Melting Furnace. Then LaFe10.85Co0.65Si1.5C0.2 and LaFe11.5Si1.5C0.2 thin strips were prepared by the strip-casting process. The DSC measurement shows that the maximum latent heat of LaFe11.5Si1.5C0.2 thin strips has been obtained after annealing at 1353 K for 12 h, longer time annealing seems to be no good for latent heat. Substitute Co for Fe could cause inhomogeneous distribution of Curie temperature (TC) in the bulk ingots, but the inhomogeneity can be improved by preparing the strip from the ingot. Under magnetic field changes of 0–1.5 T, the magnetic entropy change near the Curie temperature was about -11.1 J/kg\cdot K and -4.0 J/kg\cdot K for LaFe11.5Si1.5C0.2 and LaFe10.85Co0.65Si1.5C0.2, respectively. [ABSTRACT FROM PUBLISHER]

The compound Mn1.1Fe0.9P0.76Ge0.24 has been studied using neutron powder diffraction (NPD), differential scanning calorimeter (DSC), and magnetic measurements, in order to clarify the nature of the magnetic and structural transition and measure the associated entropy change (ΔS). The strongly first order transition occurs from a paramagnetic (PM) to a ferromagnetic (FM) phase and can be induced either by temperature or by an applied magnetic field. Our investigations indicate that the two processes exhibit identical evolutions regarding the crystal and magnetic structures, indicating they should have the same entropy change. We, therefore, conclude that the ΔSDSC obtained by the DSC method (where the transition is temperature induced) is valid also for the magnetically induced transition, thus avoiding uncertainties connected with the magnetic measurements. We have obtained the ΔSDSC = 33.8 J/kg · K for this sample upon cooling, which would increase to 42.7 J/kg · K for a impurity-free and completely homogeneous sample. For comparison, the magnetic entropy changes (ΔSM) induced by magnetic field and calculated using the Maxwell relation yields a ΔSM = 46.5J/kg · K, 38% higher than ΔSDSC. These entropy results are compared and discussed. [ABSTRACT FROM AUTHOR]

Magnetic skyrmion bubbles are swirling magnetic textures with novel characteristics suitable for future applications in spintronic devices. Here, high-density nanometric bubbles are obtained by adding C element in biskyrmion-host MnNiGa materials. Furthermore, the diversified topological spin configurations of nanometric bubbles are manipulated by combining electric current with perpendicular magnetic fields. Different magnetic bubble states including the homogeneous skyrmion bubble state are achieved via electromagnetic manipulation. Via analysing the different magnetic textures obtained via electromagnetic manipulation, we infer that the topological spin configurations of magnetic bubbles are closely related to the relative intensity of external fields applied as magnetic bubbles nucleate. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In this study, the martensite transformation of Ni 37.5 Co 12.5 Mn 35 Ti 15 ribbon was studied and regulated by the electric field-induced strain in the PMN-PT substrate. The reversible magnetocaloric effect in the Ni 37.5 Co 12.5 Mn 35 Ti 15 /PMN-PT composite was enhanced by manipulating transition paths under the coupling of magnetic field and electric field, which is significantly important for applications in solid-state refrigeration. With the assistance of E = +8 kV/cm, the reversible entropy change increased from 19.5 to 25.7 J/kgK at 294.5 K. Meanwhile, the reversible cooling temperature span was also enlarged. Hence, the reversible refrigerant capacity was enhanced from 83 to 131 J/kg, and the increase ratio reached 58%. On this basis, an active magnetic regenerating cycle facilitated by an electric field was designed. This work provides an effective method for enhancing reversible caloric effects in first-order phase transition materials via electric fields. [Display omitted] [ABSTRACT FROM AUTHOR]