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The characteristic size of the magnetocaloric materials in magnetic refrigerators, thermomagnetic regenerators and energy harvesters is usually down to micrometer and nanometer length scales, which provides the largest possible contact surface area to the heat transfer liquid. Therefore, it is pivotal to investigate the structural, magnetic and magnetocaloric properties of magnetocaloric materials at micrometer and nanometer length scales. In the present study, we have successfully fabricated MnCoGe-based thin films using the pulsed laser deposition (PLD) technique. The as-deposited film shows a dense surface, homogeneous chemical distribution and a preferred orientation along the c -axis of the hexagonal Ni 2 In-type structure. In-situ temperature-dependent X-ray diffraction measurements on the as-deposited films reveal an irreversible structural degradation above 300 °C due to the considerable evaporation of the Mn atoms, which causes the formation of microscale pores in the films. The thermomagnetic behavior of the film annealed at 250 °C displays a reversible second-order ferromagnetic transition of the hexagonal phase at Curie temperature T C = 275 K, and a first-order hexagonal-orthorhombic structural transition below 200 K. The decoupling of the magnetic and structural transitions brings reversible magnetocaloric effect with the entropy change ΔS values of 2.5 J/(kgK) and the refrigeration capacity reaching 89 J/kg in Δμ 0 H = 5 T, which are comparable to other reported magnetocaloric thin films. Moreover, antiferromagnetic coupling in the low-temperature orthorhombic phase was observed, which has rarely been reported in the MnCoGe-based bulk alloys. The different magnetic ground states between the thin film and the bulk alloys may be originated from the strain effect imposed by the Al 2 O 3 substrate. Consequently, this work not only provides insights into the structural, magnetic and magnetocaloric properties of the MnCoGe-based alloys at a nanometer length scale, but also offers a new idea for tailoring the multifunctional properties for this material family. [ABSTRACT FROM AUTHOR]

In the present work, we have demonstrated that the coupling and decoupling between the magnetic and structural transitions can be manipulated by the partial replacement of the Mn by Zr in the MnCoGe alloys. Energy-dispersive spectroscopy analyses reveal a homogeneous distribution of the Zr atoms throughout the samples. The differential scanning calorimetry and X-ray diffraction results reveal a decrease in the structural transition temperature Tt with an increase in the Zr content. A strong magneto-structural coupling can be realized in the Mn1−xZrx CoGe with 0.04 ≤ x ≤ 0.07, where the Tt is lowered to the temperature range between the Curie temperatures of the orthorhombic and hexagonal phases. The magneto-structural transition is accompanied with significant changes in the interatomic distances between the magnetic atoms, which strongly influence both the magnetic exchange interactions and the chemical bonding. As a result, a coincidence of the magnetic and structural transitions is observed, which brings a giant magnetocaloric effect due to the contributions from both the lattice and the magnetic entropy changes. [ABSTRACT FROM AUTHOR]

The fabrication of brittle magnetocaloric materials into heat exchangers is currently challenging for conventional manufacturing techniques. In the present study, we demonstrated that selective laser melting (SLM), an emerging 3D printing technique, offers a new and promising solution to fabricate the (Mn,Fe)2(P,Si) magnetocaloric alloys for magnetic refrigeration applications. The hexagonal (Mn,Fe)2(P,Si) phase, which shows a first-order magnetic transition, is successfully formed in the SLM-printed samples with a very small amount of impurity phase (less than 2% in volume fraction). The SLM processing parameters (e.g., the laser power and scanning speed) have a strong influence on the microstructure, magnetic phase transition and magnetocaloric properties of the printed samples. The microscopic mechanism underlying the changes in the microstructure and phase transition temperature has also been discussed. Besides that, a large isothermal entropy change, more than three times higher than that of the benchmark Gd material in a field change of 1 and 2 T, has been obtained in the SLM-printed samples. [ABSTRACT FROM AUTHOR]

• Pure and homogeneous MnSi is obtained via arc melting and post-annealing. • MnSi polycrystals show typical magnetic transitions as observed in single crystals. • Magnetic skyrmions can be identified in polycrystalline MnSi using magnetometry. We employed x-ray diffractometer, electron microscope and magnetometer to study the structure and magnetic properties of polycrystalline MnSi. Pure and homogeneous MnSi phase can be obtained in a certain composition range. Intriguingly, our magnetic measurements indicate that the polycrystalline MnSi shows typical magnetic phase transitions as single crystals. The magnetic transformations between helical, conical, skyrmion and field-polarized states can be well detected in the field-dependent susceptibility curves. The similar magnetic behaviors observed for polycrystalline and single crystals make magnetometry an effective and straightforward route to identify skyrmions, especially useful for the materials that are hard to prepare single crystals or epitaxial thin films. [ABSTRACT FROM AUTHOR]

Electron paramagnetic resonance (EPR) was applied extensively to probe the phase separation and spin relaxation mechanism in the perovskite manganites. In this study, we conducted the measurement of EPR for the perovskite manganites (La 0.5 Pr 0.5 ) 0.67 Ca 0.33 MnO 3 . We found that both paramagnetic and ferromagnetic resonance peaks simultaneously emerged on resonance spectrum near below T C , exhibiting a typical characteristic of phase separation. The linewidth of EPR spectrum progressively enlarged upon the rising of temperature in the temperature range of T > T C and a quasilinear variation of peak-peak width was observed at T C < T < 500 K. In contrast to the usual beliefs that the variation of peak-peak linewidth can be understood either by spin-lattice relaxation or by spin-spin relaxation, however, the linewidth behavior observed here shows a coexistence of two spin relaxation mechanisms. We proposed that the inhomogeneous electronic phases due to the intrinsic self-organizing growth were responsible for the appearance of multiple spin exchange interactions and variational relaxation mechanism. This finding would be possible to pave a new way for further investigating magnetic correlations and spin dynamics in the paramagnetic hole-doped manganites. [ABSTRACT FROM AUTHOR]

• The critical behavior of (Ce 0.65 Pr 0.35) 2 Co 7 alloy has been clarified with different methods. • The accurate Curie temperature of 214 K has been confirmed by the Arrott plot and ac magnetic susceptibility. • The magnetic coupling of (Ce 0.65 Pr 0.35) 2 Co 7 alloy belongs to long-range FM interaction. Clarification of magnetic phase transition nature and critical behavior is an essential step in the development of new magnetic functional materials. In this work, we studied critical properties of intermetallic compound (Ce 0.65 Pr 0.35) 2 Co 7 by bulk dc magnetization around the paramagnetic to ferromagnetic phase transition. It exhibits a second-order magnetic phase transition with T C = 214 K. Critical exponents β = 0.546(5) and γ = 1.054(5) are obtained by the modified Arrott plot, whereas δ = 2.843 is obtained by a critical isotherm analysis at T C. These critical exponents not only obey the Widom relation δ = 1 + γ / β , but also collapse the isothermal magnetization M-H-T data into two branches below and above T C following the single scaling equation M(H, ε) = ε β f ± (H/ ε β + γ ). Although the obtained exponents are close to the theoretical values of mean-field model, a noticeable deviation unable to be ignored, indicating the existence of localized magnetic interaction which competes with a long-range ferromagnetic state. Our results will establish a sound theoretical basis for understanding the complex magnetic interaction in the light rare earths ternary alloy. [ABSTRACT FROM AUTHOR]