Magnetic interactions in martensitic Ni-Mn-based Heusler systems

In dieser Arbeit wurden die magnetischen, magnetokalorischen sowie die strukturellen Eigenschaften Ni-Mn- basierender Heusler-Legierungen mit martensitischer Umwandlung untersucht. Ziel der Arbeit war es, die physikalischen Eigenschaften gezielt durch Modifikationen der Legierungszusammensetzung zu beeinflussen und ein Verständnis der zugrundeliegenden magnetischen Wechselwirkungen in verschiedensten kristallographischen Phasen zu erlangen. Als Ausgangspunkt wurde die Legierung Ni50Mn34In16 gewählt. Im martensitischen Zustand wird eine magnetfeldinduzierte Rückumwandlung beobachtet, die mit Dehnungen und einem inversen magnetokalorischen Effekten einhergehen. Unter Benutzung des strukturellen Phasendiagrammes martensitischer Ni-Mn-basierender Heusler-Legierungen wurde Indium durch Gallium und Zinn ersetzt. Ziel war es, die in Ni50Mn34In16 beobachteten Umwandlungstemperaturen und die damit einhergehenden Effekte zu Temperaturen nahe Raumtemperatur zu verschieben. Die unter adiabatischen Bedingungen bestimmten magnetokalorischen Eigenschaften wurden mit Hilfe eines neu konzipierten Magnetokalorimeters bestimmt. Ferner wurden Legierungen der Konzentrationsreihen Ni50Mn50-xZx (Z: Ga, Sn, In and Sb) und Ni50Mn34In16-xZx (Z: Ga and Sn) hinsichtlich der Temperaturabhängigkeit der Dehnung unter dem Einfluss externer Magnetfelder untersucht. Hierbei wurde der Einfluss des Magnetfeldfeldes auf die Nukleation martensitischer Domänen ausgenutzt. So konnten Informationen über die Richtung der leichten Achse der Magnetisierung erhalten werden. Ergänzend dazu wurden im Detail die Kristallstrukturen unter dem Einfluss eines Magnetfeldes mit Neutronen-Pulverdiffraktometrie untersucht. Hierdurch konnte gezeigt werden, dass die Austenitphase durch Kühlen im Magnetfeld in ihrer Umwandlung gehemmt ist und die Nukleation des Martensits unterdrückt wird. Mit Hilfe der Analyse polarisierter Neutronen wurden für die Legierungen Ni50Mn37Sn13 und Ni50Mn40Sb10 die magnetischen Wechselwirkungen untersucht. Es zeigte sich, dass knapp unterhalb der martensitischen Umwandlungstemperatur Ms ein antiferromagnetisch korrelierter Zustand vorliegt. Um weitere detaillierte Informationen über die Natur der magnetischen Wechselwirkungen zu erlangen, wurden für Ni50Mn37Sn13 und Ni50Mn34In16 Untersuchungen mit ferromagnetischer Resonanz durchgeführt. Damit sind die experimentell gefundenen Ergebnisse in guter Übereinstimmung mit Dichtefunktionaltheorierechnungen, die für die Legierung Ni50Mn40Sb10 angefertigt wurden. Des Weiteren wurden die Auswirkungen hydrostatischer Drücke auf die strukturellen und magnetischen Eigenschaften der Legierungen Ni50Mn50-xInx (x=15 and 16) sowie Ni50Mn40Sb10 untersucht. Hierzu wurde als Funktion der Temperatur die Magnetisierung und die Wärmetönung bestimmt sowie die Analyse polarisierter Neutronen durchgeführt. Bei Anlegen eines Magnetfeldes wurde für Ni50Mn34In16 eine Verschiebung der Ms-Temperatur von -10 K/T beobachtet. Im Gegensatz dazu verschieben hydrostatische Drücke Ms mit +4 K/kbar zu höheren Temperaturen und stabilisieren den martensitischen Zustand. Die Analyse polariserter Neutronen zeigte, dass hydrostatische Drücke antiferromagnetische Korrelationen begünstigten.In this work, magnetic, magnetocaloric and structural properties are investigated in Ni-Mn-based martensitic Heusler alloys with the aim to tailor these properties as well as to understand in detail the magnetic interactions in the various crystallographic states of these alloys. We choose Ni50Mn34In16 as a prototype which undergoes a martensitic transformation and exhibits field-induced strain and the inverse magnetocaloric effect. Using the structural phase diagram of martensitic Ni-Mn-based Heusler alloys, we substitute gallium and tin for indium to carry these effects systematically closer to room temperature by shifting the martensitic transformation. A magneto-calorimeter is designed and built to measure adiabatically the magnetocaloric effect in these alloys. The temperature dependence of strain under an external magnetic field is studied in Ni50Mn50-xZx (Z: Ga, Sn, In and Sb) and Ni50Mn34In16-xZx (Z: Ga and Sn). An argument based on the effect of the applied magnetic field on martensite nucleation is adopted to extract information on the direction of the magnetization easy axis in the martensitic unit cell in Heusler alloys. Parallel to these studies, the structure in the presence of an external field is also studied by powder neutron diffraction. It is demonstrated that martensite nucleation is influenced by cooling the sample under a magnetic field such that the austenite phase is arrested within the martensitic state. The magnetic interactions in Ni50Mn37Sn13 and Ni50Mn40Sb10 are characterized by using neutron polarization analysis. Below the martensitic transformation temperature, Ms, an antiferromagnetically correlated state is found. Ferromagnetic resonance experiments are carried out on Ni50Mn37Sn13 and Ni50Mn34In16 to gain more detailed information on the nature of the magnetic interactions. The experimental results in Ni50Mn40Sb10 show good agreement with those of density functional theory calculations. The effect of hydrostatic pressure on the structural and magnetic properties of Ni50Mn50-xInx (x= 15 and 16) and Ni50Mn40Sb10 is studied by temperature-dependent magnetization, calorimetry and polarized neutron scattering experiments. When a magnetic field is applied, Ms of Ni50Mn34In16 shifts to lower temperatures by about 10 K/T, whereas, an applied pressure shifts Ms to higher temperatures by about 4 K/kbar. Polarization analysis shows that antiferromagnetic correlations are particularly enhanced in Ni50Mn34In16 on applying pressure

Magnetization easy-axis in martensitic Heusler alloys estimated by strain measurements under magnetic-field

We study the temperature dependence of strain under constant magnetic-fields in Ni-Mn based ferromagnetic Heusler alloys in the form Ni-Mn-$X$ ($X$: Ga, In, Sn, Sb) which undergo a martensitic transformation. We discuss the influence of the applied magnetic-field on the nucleation of ferromagnetic martensite and extract information on the easy-axis of magnetization in the martensitic state.Comment: 3 pages, 3 figures. Accepted for publication in Applied Physics Letter

Effects of hydrostatic pressure on the magnetism and martensitic transition of Ni-Mn-In magnetic superelastic alloys

We report magnetization and differential thermal analysis measurements as a function of pressure accross the martensitic transition in magnetically superelastic Ni-Mn-In alloys. It is found that the properties of the martensitic transformation are significantly affected by the application of pressure. All transition temperatures shift to higher values with increasing pressure. The largest rate of temperature shift with pressure has been found for Ni$_{50}$Mn$_{34}$In$_{16}$ as a consequence of its small entropy change at the transition. Such a strong pressure dependence of the transition temperature opens up the possibility of inducing the martensitic transition by applying relatively low hydrostatic pressures.Comment: 3 pages, 3 figures. Accepted for publication in Applied Physics Letter

A Nonsurgical Approach to Treatment of High-Angle Class II Malocclusion

The bite opening effects of orthodontic appliances often cause a downward and backward mandibular rotation that only exacerbates the malocclusion. Successful orthodontic treatment of a high angle, Class II, Division 1 malocclusion requires careful consideration of the vertical dimension during treatment planning. This case report shows an individualized treatment approach to a patient with high angle Class II malocclusion

Phase diagram of Fe-doped Ni-Mn-Ga ferromagnetic shape-memory alloys

We have studied the effect of Fe addition on the structural and magnetic transitions in the magnetic shape memory alloy Ni-Mn-Ga by substituting systematically each atomic species by Fe. Calorimetric and AC susceptibility measurements have been carried out in order to study the magnetic and structural transformation properties. We find that the addition of Fe modifies the structural and magnetic transformation temperatures. Magnetic transition temperatures are displaced to higher values when Fe is substituted into Ni-Mn-Ga, while martensitic and premartensitic transformation temperatures shift to lower values. Moreover, it has been found that the electron per atom concentration essentially governs the phase stability in the quaternary system. However, the observed scaling of transition temperatures with $e/a$ differs from that reported in the related ternary system Ni-Mn-Ga.Comment: 8 pages, 8 figures. Accepted for publication in the Physical Review

Cooling and heating by adiabatic magnetization in the Ni50_{50}Mn34_{34}In16_{16} magnetic shape memory alloy

We report on measurements of the adiabatic temperature change in the inverse magnetocaloric Ni$_{50}$Mn$_{34}$In$_{16}$ alloy. It is shown that this alloy heats up with the application of a magnetic field around the Curie point due to the conventional magnetocaloric effect. In contrast, the inverse magnetocaloric effect associated with the martensitic transition results in the unusual decrease of temperature by adiabatic magnetization. We also provide magnetization and specific heat data which enable to compare the measured temperature changes to the values indirectly computed from thermodynamic relationships. Good agreement is obtained for the conventional effect at the second-order paramagnetic-ferromagnetic phase transition. However, at the first order structural transition the measured values at high fields are lower than the computed ones. Irreversible thermodynamics arguments are given to show that such a discrepancy is due to the irreversibility of the first-order martensitic transition.Comment: 5 pages, 4 figures. Accepted for publication in the Physical Review

Chilaiditi syndrome in a child with cerebral palsy presenting with recurrent abdominal pain

Introduction: The hepatodiafragmatic interposition of colon is called Chilaiditi sign. For symptomatic patients, the term “Chilaiditi syndrome” is used, this term was first reported in 1911 by Demetrius Chilaiditi, a Viennese radiologist, in three asymptomatic patients. Patients are commonly asymptomatic, and some patients may apply with gastrointestinal or respiratory symptoms such as abdominal pain or chest pain. In the study of Lekkas et al, the incidence of Chilaiditi syndrome in mental retarded patients was reported to be 63 times higher than normal population.Case Presentation: High liver dome and elevated right diaphragm, hepatic flexura replaced between liver and anterior wall of abdomen were observed in chest radiography and abdominal computer tomography of our 6,5 year old male patient with cerebral palsy who has mental retardation and recurrent abdominal pain in medical history.Conclusions: In conclusion, Chilaiditi syndrome should be considered in mental retarded children with recurrent abdominal pain.Keywords: Child, chilaiditi syndrome, recurrent abdominal pain, mental retardation, cerebral pals

Lattice dynamics in magnetic superelastic Ni-Mn-In alloys. Neutron scattering and ultrasonic experiments

Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two single crystals of Ni-Mn-In Heusler alloys close to Ni$_{50}$Mn$_{34}$In$_{16}$ magnetic superelastic composition. The paper reports the experimental determination of the low-lying phonon dispersion curves and the elastic constants for this alloy system. We found that the frequencies of the TA$_{2}$ branch are relatively low and it exhibits a small dip anomaly at a wave number $\xi_{0} \approx 1/3$, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear elastic constant $C'=(C_{11}-C_{12})/2$. Both temperature softenings are typical for bcc based solids which undergo martensitic transformations and reflect the dynamical instability of the cubic lattice against shearing of $\{110\}$ planes along $$ directions. Additionally, we measured low-lying phonon dispersion branches and elastic constants in applied magnetic fields aimed to characterize the magnetoelastic coupling.Comment: 8 pages, 7 figures. Accepted for publication in the Physical Review

Investigation of groundwater recharges mechanism in Alasehir plain: From physical characterization to modelling

IWA 2nd Regional Symposium on water, wastewater and environment, 22-24 March 2017, Cesme, İzmirCharacteristics of aquifer that allows the flow of groundwater, recharge and discharge mechanism effect the available groundwater potential. In order to determine the available potential of groundwater, the budget components are the most important parameters. In general, different analogical methods are applied in different countries, instead of using measurable data. Determination of the groundwater recharge is the most difficult parameter to be measured among the hydrological budget parameters. In general, the analogical methods are insufficient to determine the groundwater recharge rate. Precipitation, evaporation-transportation and runoff can be measured from the surface meteorological station. However, estimation of groundwater recharge cannot be measured directly. At the moment of climate change, visualization of the spatial distribution of the groundwater recharge estimation and mapping are needed. Therefore, improvements of easy groundwater recharge techniques are very important tools for groundwater basins to develop the water management planning.The Scientific and Technological Research Council of Turkey (TUBITAK), project no. 115Y06

Predicting the distribution of European Hop Hornbeam: application of MaxEnt algorithm and climatic suitability models

peer reviewedOstrya carpinifolia Scop. (European Hop Hornbeam) is a native tree in Europe as a species of the Betulaceae family. European Hop Hornbeam has a significant value for the European flora, and assessing the effects of climate change on habitats of species is essential for its sustainability. With this point of view, the main aim of the research was to predict the present and future potential distribution of European Hop Hornbeam across Europe. ‘‘IPSL-CM6A-LR’’ climate change model, ninety-six occurrence data, and seven bioclimatic variables were used to predict potential distribution areas with MaxEnt 3.4.1 program. This study applied a change analysis by comparing the present predicted potential distribution of European Hop Hornbeam with the future predicted potential distribution under the 2041–2060 and 2081–2100 SSP2 4.5 and SSP5 8.5 climate change scenarios. Study results indicated that the sum of suitable and highly suitable areas of European Hop Hornbeam is calculated to be 1,136,706 km2 for the current potential distribution. On the contrary, 2,107,187 km2 of highly suitable and suitable areas will be diminished in the worst case by 2100. The most affected bioclimatic variable is BIO 19 (Precipitation of Coldest Quarter), considering the prediction of the species distribution. These findings indicated that the natural ecosystems of the Mediterranean region will shift to northern areas. This study represented a reference for creating a strategy for the protection and conservation of the species in the future