Superstructures in Heusler compounds and investigation of their physical properties

A new tetragonal Heusler compound Mn1.4PtSn is synthesized. Crystal growth techniques that require growth directly from melt, such as Bridgman method, always result in microtwinned crystals. To get microtwin free crystals, another technique, flux method is employed, where growth can be done far below the melting point and martensitic transition temperature. The flux method results in successful large microtwin free crystals of Mn1.4PtSn. The single-crystal diffraction is done on a small piece of single crystals of Mn1.4PtSn. From structural analysis, it is found out that the crystal structure of Mn1.4PtSn is the first tetragonal superstructure in the family of Heusler compounds. The superstructure reflections are clearly observed in the powder X-ray diffraction patterns. Direction-dependent magnetic properties are measured. The compound is found to undergo two magnetic transitions. First, at 392 K, which corresponds to Curie temperature and second, at 170 K, which corresponds to the spin-reorientation transition temperature. The saturation magnetic moment at 2 K is very large of 4.7 µB/f.u. The refinement of powder neutron diffraction reveals that in the temperature range of 170 to 392 K, the magnetic structure is collinear ferromagnet whereas below 170 K, it is a non-coplanar spin structure. The magnetic moment, obtained from refinement, is close to the saturation moment obtained from magnetization. The electric transport properties are studied along the different crystallographic directions of the compound. The longitudinal resistivity measurement indicates that the compound is metallic and reveals the magnetic transitions at the same temperature as seen in the magnetization. An overall negative magnetoresistance of 3 percent is found. The Hall resistivity measurements reveal the presence of a large topological Hall resistivity (THE) of 0.9 µΩ cm and -0.1 µΩ cm for the magnetic field applied along [100] and [001], respectively. Two types of contributions in the THE for the field along [100] are seen. One that follows the quadratic form of longitudinal resistivity and second, that is independent of longitudinal resistivity. Anomalous Hall conductivity is found to be 250 and 165 Ω-1cm-1 for the field along [100] and [001], respectively. This value is close to the value obtained from theoretical calculations. The topological Hall conductivity is found to be approximately the same as its anomalous analog. A new series of polycrystalline samples with iridium substitution at the place of platinum in Mn1.4PtSn are prepared. The structural characterization show the crystal structure of these compounds is the same as Mn1.4PtSn, therefore, they also possess the tetragonal superstructure form. Magnetic properties, along with powder neutron diffraction data, reveal that the magnetic structure changes from out-of-plane ferromagnet to in-plane ferrimagnet with Ir-substitution. All the compounds are found to have metallic character. A large anomalous Hall conductivity of 405 Ω-1cm-1 is found for compound Mn1.4Pt0.7Ir0.3Sn. Three new series of compounds are prepared as an attempt to fill the vacancies present in the crystal structure of Mn1.4PtSn with transition-metal elements cobalt, nickel, and copper. The tetragonal superstructure survives up to 0.2 cobalt addition, 0.4 nickel addition and 0.6 copper addition. Further addition of elements leads to transformation to the inverse cubic Heusler structure. The magnetic properties show that the compounds with tetragonal structure have spin-reorientation transition, which is absent in the compounds with cubic structure. A new compound Mn1.7Pt0.8In is discovered. The single crystals are prepared by flux-method. Upon structural analysis from single-crystal refinement, it is found that the crystal structure is 3 × 3 × 3 superstructure of a Heusler structure and is so far the largest discovered in the Heusler family of compounds. Two magnetic transitions are revealed in the magnetization measurements. First, at 330 K, which corresponds to Curie temperature and second, at 220 K, which corresponds to spin-reorientation transition. The magnetic moment is 0.4 µB/Mn at 2 K and 0.07 µB/Mn at 300 K. Such a low moment might be due to possible compensated ferrimagnetic structure. Therefore, the compound is a potential candidate for spintronics devices

Anisotropic Topological Hall Effect with Real and Momentum Space Berry Curvature in the Antiskrymion Hosting Heusler Compound Mn1.4_{1.4}PtSn

The topological Hall effect (THE) is one of the key signatures of topologically non-trivial magnetic spin textures, wherein electrons feel an additional transverse voltage to the applied current. The magnitude of THE is often small compared to the anomalous Hall effect. Here, we find a large THE of 0.9 $\mu\Omega$cm that is of the same order of the anomalous Hall effect in the single crystalline antiskyrmion hosting Heusler compound Mn$_{1.4}$PtSn, a non-centrosymmetric tetragonal compound. The THE is highly anisotropic and survives in the whole temperature range where the spin structure is noncoplanar (<170 K). The THE is zero above the spin reorientation transition temperature of 170 K, where the magnetization will have a collinear and ferromagnetic alignment. The large value of the THE entails a significant contribution from the momentum space Berry curvature along with real space Berry curvature, which has never been observed earlier

Antiskyrmions and their electrical footprint in crystalline mesoscale structures of Mn1.4PtSn

Skyrmionic materials hold the potential for future information technologies, such as racetrack memories. Key to that advancement are systems that exhibit high tunability and scalability, with stored information being easy to read and write by means of all-electrical techniques. Topological magnetic excitations such as skyrmions and antiskyrmions, give rise to a characteristic topological Hall effect. However, the electrical detection of antiskyrmions, in both thin films and bulk samples has been challenging to date. Here, we apply magneto-optical microscopy combined with electrical transport to explore the antiskyrmion phase as it emerges in crystalline mesoscale structures of the Heusler magnet Mn1.4PtSn. We reveal the Hall signature of antiskyrmions in line with our theoretical model, comprising anomalous and topological components. We examine its dependence on the vertical device thickness, field orientation, and temperature. Our atomistic simulations and experimental anisotropy studies demonstrate the link between antiskyrmions and a complex magnetism that consists of competing ferromagnetic, antiferromagnetic, and chiral exchange interactions, not captured by micromagnetic simulations

Taking stock of 10 years of published research on the ASHA programme: Examining India’s national community health worker programme from a health systems perspective

Background: As India’s accredited social health activist (ASHA) community health worker (CHW) programme enters its second decade, we take stock of the research undertaken and whether it examines the health systems interfaces required to sustain the programme at scale. Methods: We systematically searched three databases for articles on ASHAs published between 2005 and 2016. Articles that met the inclusion criteria underwent analysis using an inductive CHW–health systems interface framework. Results: A total of 122 academic articles were identified (56 quantitative, 29 mixed methods, 28 qualitative, and 9 commentary or synthesis); 44 articles reported on special interventions and 78 on the routine ASHA program. Findings on special interventions were overwhelmingly positive, with few negative or mixed results. In contrast, 55% of articles on the routine ASHA programme showed mixed findings and 23% negative, with few indicating overall positive findings, reflecting broader system constraints. Over half the articles had a health system perspective, including almost all those on general ASHA work, but only a third of those with a health condition focus. The most extensively researched health systems topics were ASHA performance, training and capacity-building, with very little research done on programme financing and reporting, ASHA grievance redressal or peer communication. Research tended to be descriptive, with fewer influence, explanatory or exploratory articles, and no predictive or emancipatory studies. Indian institutions and authors led and partnered on most of the research, wrote all the critical commentaries, and published more studies with negative results. Conclusion: Published work on ASHAs highlights a range of small-scale innovations, but also showcases the challenges faced by a programme at massive scale, situated in the broader health system. As the programme continues to evolve, critical comparative research that constructively feeds back into programme reforms is needed, particularly related to governance, intersectoral linkages, ASHA solidarity, and community capacity to provide support and oversight

Superstructures in Heusler compounds and investigation of their physical properties

A new tetragonal Heusler compound Mn1.4PtSn is synthesized. Crystal growth techniques that require growth directly from melt, such as Bridgman method, always result in microtwinned crystals. To get microtwin free crystals, another technique, flux method is employed, where growth can be done far below the melting point and martensitic transition temperature. The flux method results in successful large microtwin free crystals of Mn1.4PtSn. The single-crystal diffraction is done on a small piece of single crystals of Mn1.4PtSn. From structural analysis, it is found out that the crystal structure of Mn1.4PtSn is the first tetragonal superstructure in the family of Heusler compounds. The superstructure reflections are clearly observed in the powder X-ray diffraction patterns. Direction-dependent magnetic properties are measured. The compound is found to undergo two magnetic transitions. First, at 392 K, which corresponds to Curie temperature and second, at 170 K, which corresponds to the spin-reorientation transition temperature. The saturation magnetic moment at 2 K is very large of 4.7 µB/f.u. The refinement of powder neutron diffraction reveals that in the temperature range of 170 to 392 K, the magnetic structure is collinear ferromagnet whereas below 170 K, it is a non-coplanar spin structure. The magnetic moment, obtained from refinement, is close to the saturation moment obtained from magnetization. The electric transport properties are studied along the different crystallographic directions of the compound. The longitudinal resistivity measurement indicates that the compound is metallic and reveals the magnetic transitions at the same temperature as seen in the magnetization. An overall negative magnetoresistance of 3 percent is found. The Hall resistivity measurements reveal the presence of a large topological Hall resistivity (THE) of 0.9 µΩ cm and -0.1 µΩ cm for the magnetic field applied along [100] and [001], respectively. Two types of contributions in the THE for the field along [100] are seen. One that follows the quadratic form of longitudinal resistivity and second, that is independent of longitudinal resistivity. Anomalous Hall conductivity is found to be 250 and 165 Ω-1cm-1 for the field along [100] and [001], respectively. This value is close to the value obtained from theoretical calculations. The topological Hall conductivity is found to be approximately the same as its anomalous analog. A new series of polycrystalline samples with iridium substitution at the place of platinum in Mn1.4PtSn are prepared. The structural characterization show the crystal structure of these compounds is the same as Mn1.4PtSn, therefore, they also possess the tetragonal superstructure form. Magnetic properties, along with powder neutron diffraction data, reveal that the magnetic structure changes from out-of-plane ferromagnet to in-plane ferrimagnet with Ir-substitution. All the compounds are found to have metallic character. A large anomalous Hall conductivity of 405 Ω-1cm-1 is found for compound Mn1.4Pt0.7Ir0.3Sn. Three new series of compounds are prepared as an attempt to fill the vacancies present in the crystal structure of Mn1.4PtSn with transition-metal elements cobalt, nickel, and copper. The tetragonal superstructure survives up to 0.2 cobalt addition, 0.4 nickel addition and 0.6 copper addition. Further addition of elements leads to transformation to the inverse cubic Heusler structure. The magnetic properties show that the compounds with tetragonal structure have spin-reorientation transition, which is absent in the compounds with cubic structure. A new compound Mn1.7Pt0.8In is discovered. The single crystals are prepared by flux-method. Upon structural analysis from single-crystal refinement, it is found that the crystal structure is 3 × 3 × 3 superstructure of a Heusler structure and is so far the largest discovered in the Heusler family of compounds. Two magnetic transitions are revealed in the magnetization measurements. First, at 330 K, which corresponds to Curie temperature and second, at 220 K, which corresponds to spin-reorientation transition. The magnetic moment is 0.4 µB/Mn at 2 K and 0.07 µB/Mn at 300 K. Such a low moment might be due to possible compensated ferrimagnetic structure. Therefore, the compound is a potential candidate for spintronics devices

Superstructures in Heusler compounds and investigation of their physical properties

A new tetragonal Heusler compound Mn1.4PtSn is synthesized. Crystal growth techniques that require growth directly from melt, such as Bridgman method, always result in microtwinned crystals. To get microtwin free crystals, another technique, flux method is employed, where growth can be done far below the melting point and martensitic transition temperature. The flux method results in successful large microtwin free crystals of Mn1.4PtSn. The single-crystal diffraction is done on a small piece of single crystals of Mn1.4PtSn. From structural analysis, it is found out that the crystal structure of Mn1.4PtSn is the first tetragonal superstructure in the family of Heusler compounds. The superstructure reflections are clearly observed in the powder X-ray diffraction patterns. Direction-dependent magnetic properties are measured. The compound is found to undergo two magnetic transitions. First, at 392 K, which corresponds to Curie temperature and second, at 170 K, which corresponds to the spin-reorientation transition temperature. The saturation magnetic moment at 2 K is very large of 4.7 µB/f.u. The refinement of powder neutron diffraction reveals that in the temperature range of 170 to 392 K, the magnetic structure is collinear ferromagnet whereas below 170 K, it is a non-coplanar spin structure. The magnetic moment, obtained from refinement, is close to the saturation moment obtained from magnetization. The electric transport properties are studied along the different crystallographic directions of the compound. The longitudinal resistivity measurement indicates that the compound is metallic and reveals the magnetic transitions at the same temperature as seen in the magnetization. An overall negative magnetoresistance of 3 percent is found. The Hall resistivity measurements reveal the presence of a large topological Hall resistivity (THE) of 0.9 µΩ cm and -0.1 µΩ cm for the magnetic field applied along [100] and [001], respectively. Two types of contributions in the THE for the field along [100] are seen. One that follows the quadratic form of longitudinal resistivity and second, that is independent of longitudinal resistivity. Anomalous Hall conductivity is found to be 250 and 165 Ω-1cm-1 for the field along [100] and [001], respectively. This value is close to the value obtained from theoretical calculations. The topological Hall conductivity is found to be approximately the same as its anomalous analog. A new series of polycrystalline samples with iridium substitution at the place of platinum in Mn1.4PtSn are prepared. The structural characterization show the crystal structure of these compounds is the same as Mn1.4PtSn, therefore, they also possess the tetragonal superstructure form. Magnetic properties, along with powder neutron diffraction data, reveal that the magnetic structure changes from out-of-plane ferromagnet to in-plane ferrimagnet with Ir-substitution. All the compounds are found to have metallic character. A large anomalous Hall conductivity of 405 Ω-1cm-1 is found for compound Mn1.4Pt0.7Ir0.3Sn. Three new series of compounds are prepared as an attempt to fill the vacancies present in the crystal structure of Mn1.4PtSn with transition-metal elements cobalt, nickel, and copper. The tetragonal superstructure survives up to 0.2 cobalt addition, 0.4 nickel addition and 0.6 copper addition. Further addition of elements leads to transformation to the inverse cubic Heusler structure. The magnetic properties show that the compounds with tetragonal structure have spin-reorientation transition, which is absent in the compounds with cubic structure. A new compound Mn1.7Pt0.8In is discovered. The single crystals are prepared by flux-method. Upon structural analysis from single-crystal refinement, it is found that the crystal structure is 3 × 3 × 3 superstructure of a Heusler structure and is so far the largest discovered in the Heusler family of compounds. Two magnetic transitions are revealed in the magnetization measurements. First, at 330 K, which corresponds to Curie temperature and second, at 220 K, which corresponds to spin-reorientation transition. The magnetic moment is 0.4 µB/Mn at 2 K and 0.07 µB/Mn at 300 K. Such a low moment might be due to possible compensated ferrimagnetic structure. Therefore, the compound is a potential candidate for spintronics devices

Cutaneous polyarteritis nodosa: A rare isolated cutaneous vasculitis

Cutaneous polyarteritis nodosa (CPAN) is a rare form of cutaneous vasculitis that involves small and medium sized arteries of the dermis and subcutaneous tissue without systemic involvement. It presents with tender subcutaneous nodules, digital gangrene, livedo reticularis and subcutaneous ulcerations. The diagnosis is by skin biopsy and characteristic pathologic feature is a leukocytoclastic vasculitis in the small to medium-sized arterioles of the dermis. We report a rare case of benign cutaneous PAN in a 14-year-old girl who presented with history of fever, subcutaneous nodules with cutaneous ulcer and digital gangrene. The skin biopsy showed leukocytoclastic vasculitis with fibrinoid necrosis in the dermal vessels. She received treatment with steroids and lesions resolved completely over a period of month