Fe2−xCoxP1−ySiy has attracted significant attention for magnet applications due to its promising intrinsic magnetic properties and the absence of strategic elements, such as rare earths (RE). Most samples reported in the literature are polycrystalline, obtained via mechanical alloying, which makes direct measurement of magnetocrystalline anisotropy challenging. Only a limited number of single-crystal compositions have been characterized. In this work, we have produced Fe2−xCoxP1−ySiy polycrystalline samples by combined induction and arc melting techniques. The obtained samples have a better degree of purity with respect to mechanical alloyed samples reported in literature, with secondary phase appearing only in specimens containing large Si quantities. In addition, this work builds upon prior single crystal studies by providing a comprehensive characterization of a broader range of compositions 0.1 ≤ x ≤ 0.3 and 0.1 ≤ y ≤ 0.4, including the first direct and systematic measurement of the anisotropy field in Fe2−xCoxP1−ySiy polycrystalline samples. Results show that the maximum anisotropy field µ0HA = 2.84 T is obtained in Fe1.90Co0.10P0.80Si0.20, with saturation magnetization MS = 111 Am2/kg and Curie temperature TC = 495 K. The theo retical maximum energy product approaches 200 kJ/m3, which makes this material one of the most promising for RE-free permanent magnets with intermediate performances between fer rite and RE-magnets. Experimental results were complemented by DFT calculations in order to estimate magnetic moment and magnetocrystalline anisotropy energy (MAE) maps for a wider range of compositions. Computational results show that band filling plays a role in the optimization of MAE in the Fe2−xCoxP1−ySiy system.

Complex perovskite oxides stabilized under high-pressure conditions constitute a rich playground for material science thanks to their multifunctional properties. Here we present the synthesis of BiCu0.4Mn0.6O3, obtained under isotropic high-pressure/high-temperature conditions. The compound crystallizes in the orthorhombic Pbam space group with a = 5.57960(16) & Aring;, b = 11.2374(3) & Aring;, c = 7.6603(2) & Aring;. Disorder between Cu and Mn cations at the B site causes a significant interplay between electric and magnetic properties. Although a long-range magnetic order is not observed in neutron diffraction, BiCu0.4Mn0.6O3 displays a ferromagnetic-like transition at 330 K confined at the local scale and thermal-activated semiconductive behavior. At lower temperatures, the partial electronic localization on the Mn site changes the transport mechanism leading to 3D variable range hopping conductivity and determines the formation of an antiferromagnetic ordering at about 30 K. The presence of ferromagnetic-like room temperature state makes this material intriguing as a starting point for advanced multifunctional devices.

Magnetic hyperthermia is a non-invasive cancer therapy method resulting in cell apoptosis. The method is based on generating heat by magnetic nanoparticles in external magnetic fields. One of the main challenges however is to control the temperature of the particles to avoid overheating which would also damage healthy tissues. Here, we introduce magnetic-shape-memory Heusler particles as a potential self-regulating magnetic hyperthermia agent thanks to a sharp reversible magnetostructural phase transformation. We demonstrate that Ni-Mn-Cu-Ga particles can be designed to heat-up to a desired temperature (by high-frequency alternating magnetic fields), above which they undergo the phase transformation, therefore, lose their magnetic properties and the capability of magnetic-field-induced heating, thereby showing a "self-regulating" magnetic hyperthermia effect. We analyze the obtained data by numerical calculations, highlighting the major heat dissipation mechanisms and the critical role of sharpness of the magnetostructural phase transformation (martensite-austenite) in Ni49.7Mn18.7-Cu6.4Ga25.2 on the self-regulation effect. Besides, we show the effects of air pressure, power input, dispersant and starting temperature on the attained final equilibrium temperature.

One of the possible approaches to decrease the demand for critical elements such as rare earths is to develop new sustainable magnets. Iron-based materials are suitable for gap magnets applications since iron is the most abundant ferromagnetic element on Earth. Fe5SiB2 is a candidate as gap magnet thanks to its high Curie temperature (T-C similar to 800 K) and specific saturation magnetization (M-S similar to 140 Am(2)kg(-1)). However its anisotropy field is too low for applications (mu H-0(A) similar to 0.8 T). In order to increase the anisotropy value, we synthesized a series of Ge, Re and Cr substituted Fe5SiB2 compounds and studied their magnetic properties. They all crystallize in the Cr5B3-type tetragonal structure with the I4/mcm space group. Curie temperature (T-C = 803 K) and specific saturation magnetization (M-S = 138 Am(2)kg(-1)) are slightly decreased by elemental substitution with Re having the largest effect. Despite being reduced, T-C and M-S still maintain significant values (T-C > 750 K and M-S = 118 Am(2)kg(-1)). The room temperature anisotropy field has been measured by Singular Point Detection (SPD) and increases by about 15 % upon Re substitution, reaching 0.92 T for Fe4.75Re0.25SiB2. We have also used Nuclear Magnetic Resonance and SPD measurements to study the spin reorientation transition which takes place at 172 K and we have found that it is partially suppressed by substitution of Ge from 172 K to 140 K and completely suppressed upon Cr and Re substitution.

The generation of high magnetic pulsed fields involves several technological challenges. State-of-the-art field peak intensities can be achieved by means of double-coil systems and, as for other configurations, a special pick-up system is required to clean the signal from spurious components and artifacts. However, the design of a well-balanced pick-up for double-coil systems is not a trivial task because of the different mutual inductance of the two field coils. In general the pick-up can be optimized for one coil only, but not for both. Here we present a new pick-up concept specifically aimed at solving this problem, based on an active compensation bridge and a special compensating coil located outside field-generating coils. Besides yielding a good balance of the signal over all pulse duration, a further advantage is an additional increase in the signal-to-noise ratio.

We investigate the electric properties of Pb2FeMoO6 (PFMO), a double perovskite that can be grown in a bulk pure phase only via High Pressure/High Temperature solid-state reaction. The as -obtained PFMO is characterized by a high degree of cationic ordering at the B site between Fe3+ and Mo5+ and a ferrimagnetic transition with TN around 275 K. A semi -metallic to half -metallic transition seems to occur when the ferrimagnetic order arises thanks to the localization of a minority fraction of electrons on the Mo site. In this thermal regime, the system displays asymmetric magneto -resistivity, with selective -polarized carriers promoted by intense negative magnetic fields applied across the Ne ' el transition during the cooling ramp. This cation -ordering related feature vanishes when the Mo-O bond length stabilizes, indicating a strong connection between the magnetic and electrical properties of this compound.

Struvite (MgNH4PO46H2O) is a mineral first identified in 1845. It is being tested for several reasons: (1) it is a problem in liquid wastewater treatment plants; (2) on the other hand, it is recovered from these wastewaters for its phosphorus, magnesium and nitrogen; (3) is the main component of microbial-induced urinary stones. We have recently shown that struvite is ferroelectric and piezoelectric. In this paper, we present the first experimental evidence of the pyroelectric nature of struvite. Using a single-diffusion gel growth technique, we grew struvite crystals as flat, parallel plates. We performed measurements of pyroelectric currents on struvite of this shape, using it as a dielectric of a plate capacitor. The occurrence of pyroelectric effects in struvite was investigated by measuring depolarization currents as a function of temperature. This technique allows the disclosure of ferroelectric/pyroelectric transitions as well as the reconstruction of the ferroelectric loop. We found that the value of the pyroelectric coefficient p attains a maximum of 22 x 10-6 C m-2 K-1 slightly below room temperature, going down to p congruent to 10 x 10-6 C m-2 K-1 at room temperature. This value is comparable to values for other minerals. For example, the pyroelectric polarization coefficient of tourmaline, the mineral for which the pyroelectric effect was first discovered, is 4 x 10-6 C m-2 K-1. This value is 2.5 times lower than that measured for struvite, illustrating struvite's fairly strong pyroelectricity. Struvite (MgNH4PO46H2O) is a mineral first identified in 1845.

Nanoindentation was used to analyze the effect of localized plastic deformation on the martensitic trans-formation of epitaxial Ni-Mn-Ga films on MgO(001) substrate. Atomic and magnetic force microscopy imaging at elevated temperature was applied to study the martensitic transformation route from the nanometer to the micrometer scale. We analyzed the cooling and heating curves for the martensitic transformation of the nano-indented areas as a function of the applied loads as well as the distance from the material pile-ups around the residual impressions. We observe a thermodynamically governed local increase of the martensitic transformation temperature (i.e. martensite stabilization) as a function of the applied loads. The local increase of the trans-formation temperature vs. the applied load (P) follows a non-linear regime: reducing the slope by increasing the applied load and showing a plateau for P >= 5 mN. The observed effect is local and almost disappears for distances larger than 500 nm from the pile-ups around the residual impressions, where the material transforms similar to the pristine sample. The local increase of transformation temperature as a function of nanoindentation loads is the dominant effect and occurs in both the cooling and the heating curves. Therefore, no considerable thermal hysteresis variation is observed in the transformation of the material. Moreover, we report in average similar to 12% higher relative areal shift of the transformation curves over cooling than heating close to the indents reflecting an unequal impact of indents on T-M and T-A in Ni-Mn-Ga.

By means of single-crystal X-ray diffraction we have revealed the breaking of centrosymmetry when lowering the temperature under T_s = 200 K concomitantly with the setting of a commensurate superstructure in the small A-site quadruple perovskite YMn_3Mn_4O_12. This results is in agreement with all data already reported for this compounds and solve the previous inconsistency about the Yttrium position. The superstructure is characterized by the appearing of satellite reflections in the single crystal pattern, consistent with an I-centered pseudo-orthorhombic commensurate supercell with a ≈√(a_F) = 10.4352(7) Å, b ≈ 2b_F = 14.6049(9) Å, c ≈√(c_F) = 10.6961(7) Åand β = 90.110(3)^∘, where F stands for the "fundamental" high-temperature cell (a_F ≈ c_F ≈ 7.45 Å, b_F ≈ 7.34 Å, and β≈ 90^∘). The space-group was unequivocally found to be Ia, which is non polar, thus allowing for a non-zero polarization in the material. We then have investigated in detail the pyrocurrent, transport, dielectric and the DC and AC magnetic properties of polycrystalline sample of YMn_3Mn_4O_12 over a wide temperature range. These measurements clearly highlight several critical temperatures in the material and correlation between the different orders: i) the centrosymmetry is broken at high temperature (T_S = 200K), ii) then the long-range magnetic order of B-sites occurs at T_N,B = 108 K and at this same temperature the compound enters in an insulating dielectric state. iii) Finally, a remnant polarization is stabilized concomitantly with a magnetic anomaly at T* = 70 K. We propose that YMn_3Mn_4O_12 is a peculiar magnetic ferroelectric in which the polar state is driven by short-range magnetic order.

Shape morphing materials, especially those fabricated by 4D printing, are gaining much attention due to their versatility of actuation and capability of being programmed in advance. These materials become particularly interesting for biomedical applications where implant materials could be remotely actuated, exerting a force on the surrounding tissues and cells. However, applications in this field have been restricted due to the biocompatibility of the materials and the character of the required stimuli, generally not compatible with physiological environments. Magnetic nanoparticles (MNPs) represent a great opportunity to this end; however, the actuation results in a uniform movement toward the magnet that requires anchoring of the object. Here, for the first time, the application of anisotropic Fe3O4 MNPs is described, and synthesized by a novel and easy route, that can be aligned on pre‐defined patterns within objects printed by digital light processing, resulting in materials that can be actuated remotely (4D printing). These nanoparticles (178 nm × 55 nm), show good biocompatibility when directly seeded on top of human mesenchymal stem cells, despite being uptaken. Most importantly, the alignment of the MNPs can tune the movement of fabricated nanocomposite materials, resulting in complex movements of attraction or repulsion depending on the direction of the applied magnetic field.

We present a study on the Curie transition of austenitic Ni-Mn-In full Heusler compounds when Mn atoms are replaced by Fe or Cu. The substituted compounds are designed to present a relevant magnetocaloric effect at the second order Curie transition of the austenitic phase near room temperature. We show that Fe and Cu modify the magnetic moments and interactions responsible of the localized magnetism in the L21 ordered cubic structure, resulting in a change of the Curie temperature and saturation magnetization of the compound. Neutron diffraction experiments and electron microscopy analysis were used to study the sites occupancy of doping atoms and the presence of secondary phases, thus possibly optimizing the annealing protocols to obtain homogeneous samples even at high Cu/Fe concentrations. On this basis, a series of quinary compounds with a tunable Curie temperature and high values of saturation magnetization (100-110 Am2/kg at 80 K) was successfully synthesized. The obtained results show the feasible fine tuning of the Curie temperature at which the peak of the magnetocaloric effect is realized, highlighting a new promising strategy to design graded regenerators for room temperature magnetocaloric applications. 0 2021 Elsevier B.V. All rights reserved.

4D Printed Shape-Morphing Biocompatible Materials with Unpaired Movements 4D printed shape-morphing materials allow for remote and reversible actuation of pre-defined structures. In article number 2202539, Lorenzo Moroni and co-workers demonstrate that these reversible actuation can be programed to display patterns of attraction and repulsion within same object while using composites based on biocompatible anisotropic nanomagnets.

The low-temperature structure of Bi0.68Ca0.32MnO3 has been solved from electron and neutron diffraction data. The quantitative simultaneous refinement indicates an ordering of the Mn cations in a "stripe/chess"-like pattern. The ordering is accompanied by the formation of short Mn-Mn distances and the rearrangement of the Mn-O bonds indicating the development of complex extended "orbital molecules." The primary order parameter breaks inversion symmetry and allows the generation of a spontaneous electrical polarization as the secondary order parameter. The neutron data at low temperature indicate the coexistence of a pseudo-CE long-range-ordered structure with a strongly reduced moment and short-range ferromagnetic correlations. These results indicate an intricate competition between the charge, orbital, and magnetic degrees of freedom and the Bi3+ stereoactivity in this manganite system.

The low temperature phenomenology of Strontium Titanate is rich and intriguing, with anomalies producing signals of small intensity. We show that depolarization pyrocurrents are a suitable technique to greatly enhance these features, otherwise rather elusive when observed with other methods. Depolarization currents have been measured on a single phase sintered SrTiO3 pellet, prepared by solid state reaction. They increase with increasing poling voltage and switch to symmetric negative values by inversion of the poling sign, which is a property commonly considered as a clue of ferroelectricity. Moreover, three intensity maxima are revealed at T=16, 24 and 45 K respectively. In particular, the anomaly at T ≃ 45 K can be associated with the emerging of ferroelectricity in walls between antiphase ferroelastic domain walls, whose nanoscale polar character is already known from literature.We demonstrate and estimate such ferroelectricity reconstructing a static polarization hysteresis loop by applying suitable poling patterns.

The structural and magnetic properties of Sr0.67Ca0.33Fe9Al3-xCrxO19 submicrometric powders with sub-stitution levels ranging from x = 0 up to x = 3, prepared by sol-gel synthesis method, have been investigated. The powders were characterized by high resolution synchrotron X-ray diffraction, scanning electron microscopy, powder neutron diffraction and MPMS-SQUID magnetometer. The structural analysis shows that upon Ca-substitution of SrFe12O19 at the Sr site and Al-Cr at the Fe sites, the magnetoplumbite structure is preserved, even for large levels of substitutions. The X-ray powder diffraction peak broadening and Williamson-Hall plots analyses indicate an increase of crystallites size and relaxation of the microstrain with increasing amounts of Chromium. The magnetic hysteresis loops reveal high coercivity fields at room temperature, with the highest value of H-C = 1125 kA/m (1.41 T) obtained for Sr0.67Ca0.33Fe9Al2.5Cr0.5O19 powder interesting to develop free-Rare Earth high coercivity magnets. The saturation magnetization and remanence values increase monotonically with increasing Cr content while the switching field decreases. The structural Rietveld refinement of combined X-ray/neutron diffraction data shows the affinity of Al3+ and Cr3+ cations to migrate mainly towards (2 alpha) Fe-Oh2 and (12k) Fe-Oh3 sites and only minor amounts is found on the (4f1) Fe-Oh1 octahedral sites. The structural observations corroborate the magnetic properties, demonstrating a correlation between the structure and magnetic properties in Ca-Al-Cr substituted strontium hexaferrite. The role of the particle size to maximize the coercivity properties is discussed. (C) 2021 Published by Elsevier B.V.

Ferromagnetic-shape-memory (FSM) Heuslers are a class of smart materials, promising for integration into miniaturized thermo/magnetomechanical devices, applicable in automotive, aerospace, biology, and robotics fields. In addition to compactness and mechanical simplicity, it is crucial for the material to maintain its properties at micro and nanometer scales. This study evidences the effects of lateral dimension and geometry on the properties of FSM Heuslers in patterned epitaxially grown Ni-Mn-Ga films. In particular, arrays of microstructures with lateral sizes down to the micrometer range, having different shapes and orientations with respect to the substrate edges, are investigated. The key properties of the material are stable after the microfabrication process: the martensitic transition temperatures increase by less than 3 K and thermal hysteresis changes by only 2 K. Notably, the size and geometry (i.e. shape and orientation) of the patterned microstructures are reported to be a suitable tool for controlling the martensitic configuration. The study demonstrates selective response of a specific type of martensitic twin boundaries, i.e., X-type twin boundaries along [110] MgO and [1-10] MgO, to the shape and orientation of the microstructures showing a twin boundary selection of up to similar to 96%. The effects of lateral size, shape, and orientation on the martensitic and magnetic properties of the lithographically patterned structures are discussed. (C) 2021 Elsevier Ltd. All rights reserved.

Ferromagnetic-shape-memory (FSM) Heusler compounds are an important class of multifunctional mate-rials having promising applications in a vast variety of areas such as actuating, sensing, energy harvesting, spintronics and multicaloric cooling. Their multifunctionality stems from a reversible martensitic phase transition. However, their full exploitation is prevented by some undesirable characteristics of the marten-sitic transition: thermal hysteresis and broad transition. We studied here the role of specific martensitic configurations on the transition characteristics. By advanced magnetic force microscopy imaging in a wide temperature (260-350 K) and magnetic field range (up to 14 T) we directly observed the nucleation and the self-accommodation of the martensitic twinning configurations under zero-field, isofield and isother-mal conditions. The experiments were performed on Ni-Mn-Ga epitaxial thin films with martensitic twin-ning configurations made of both X-and Y-type, which are characterized by different orientations of the twinning planes (i.e. at 45 degrees and 90 degrees degrees to the (001) MgO substrate, respectively). We have found that between the two possible twinning configurations, the Y-type, which nucleates first, shows a signif-icantly smaller thermal hysteresis as well as a sharper phase transition with respect to X-type twinning configuration, for all the three investigated conditions. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In the last few years, significant effort has again been devoted to ferrite-based permanent magnet research due to the so-called rare-earth crisis. In particular, a quest to enhance ferrites maximum energy product, BH max , is underway. Here, the influence of composition and sintering conditions on the microstructure and consequently magnetic properties of strontium ferrite-based hybrid composites was investigated. The powder mixtures consisted of hydrothermally synthesised Sr-ferrite with hexagonally shaped platelets with a diameter of 1 μ m and thickness up to 90 nm, and a soft magnetic phase in various ratios. Powders were sintered using a spark plasma sintering furnace. The crystal structure, composition and microstructure of the starting powders and hybrid magnets were examined. Their magnetic properties were evaluated by vibrating sample magnetometer, permeameter and by single-point-detection measurements.

We present a study on the correlation of the superconducting critical temperature (Tc) and structural morphology with a chemically substituted high-temperature superconductor (HTS) (Bi,Pb)-2212 via Powder X-ray Diffraction (PXRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX), anddcmagnetometry. The elements Zn, Y, Ti, and Nd are incorporated within the bismuth cuprate structure at amounts that extend the ranges currently found in literature.