53 research outputs found
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Magnetic phase diagram of the mn<sub>x</sub> fe<sub>2−x</sub> p<sub>1−y</sub> si<sub>y</sub> system
No full textThe phase diagram of the magnetocaloric Mnx Fe2−x P1−y Siy quaternary compounds was established by characterising the structure, thermal and magnetic properties in a wide range of compositions (for a Mn fraction of 0.3 ≤ x < 2.0 and a Si fraction of 0.33 ≤ y ≤ 0.60). The highest ferromagnetic transition temperature (Mn0.3 Fe1.7 P0.6 Si0.4, TC = 470 K) is found for low Mn and high Si contents, while the lowest is found for low Fe and Si contents (Mn1.7 Fe0.3 P0.6 Si0.4, TC = 65 K) in the Mnx Fe2−x P1−y Siy phase diagram. The largest hysteresis (91 K) was observed for a metal ratio close to Fe:Mn = 1:1 (corresponding to x = 0.9, y = 0.33). Both Mn-rich with high Si and Fe-rich samples with low Si concentration were found to show low hysteresis (≤2 K). These compositions with a low hysteresis form promising candidate materials for thermomagnetic applications.RST/Fundamental Aspects of Materials and Energ
Giant magnetocaloric effect for (Mn, Fe, V)2(P, Si) alloys with low hysteresis
No full textThe Fe2P type Mn–Fe–P–Si alloys exhibit a giant magneto-elastic first-order transition, but the large hysteresis limits their performance. Crystal structure evolution and magnetocaloric performance were investigated by varying the Mn and Fe contents at a constant V substitution of 0.02 in Fe2P-type (Mn1.17-xFe0.73-yV0.02) (P0.5Si0.5) (where x + y = 0.02). The V substitution of Fe content shows a larger reduction of hysteresis compared with the same substitution amount of Mn content. During magnetoelastic phase transition, V-substitution reduces the volume change and the volumetric stresses, providing a superior mechanical stability. Compound with the V substitution of Fe (y = 0.02) shows the best magnetocaloric effect with a low thermal hysteresis of 0.6 K. Our developed Mn1.17-xFe0.73-yV0.02P0.5Si0.5 alloys are excellent materials for room-temperature magnetic heat-pumping applications by using a permanent magnet
Effect of prior cyclic damage removal on high temperature low cycle fatigue endurance
No full textAbstractIn terms of fatigue life recovery, the beneficial effect of removing a surface layer from critical locations of components subject to high frequency elastic loading is well documented. Not so well known are the consequences of surface layer removal from parts previously subject to elasto-plastic low cycle fatigue (LCF) loading. The paper describes the results of a research project conducted to evaluate the effects of surface layer removal on subsequent LCF properties using uniaxial testpieces which have been prior cyclic deformed to different life fractions. Strain-controlled LCF tests performed on a 1%CrMoV steel at 565 °C with different strain amplitudes indicate that, following: (i) prior cyclic deformation (PCD) to nominal LCF life fractions of 0.5 and 0.8, (ii) subsequent surface damage layer removal, and (iii) test resumption; the consequent overall LCF endurances are at least as long as those accumulated without intermediate surface damage removal, and in some cases are significantly extended. Unlike the possibilities associated with elastic fatigue loading, LCF lifetimes are not fully recoverable following the removal of prior cyclic surface damage
Mixed magnetism in magnetocaloric materials with first-order and second-order magnetoelastic transitions
No full textTemperature dependent high-resolution x-ray diffraction measurements were used to characterize the magneto-elastic ferromagnetic transition of (Fe,Mn)2(P,Si,B) compounds. Across the transition, apart from a change in lattice parameters across the transition, the internal coordinates of Mn and Fe also change. This intrinsic degree of freedom allows Fe in the tetrahedral coordination to decrease the two interatomic distances with the 2c position and increase the two distances with the two 1b position, while the Fe–Mn distance remains constant. For Mn in the square based pyramidal coordination, all interatomic distances effectively remain constant. Electron density plots show that for second-order transitions, the observed changes are smaller and continuously extending over a wide temperature range in the ferromagnetic and paramagnetic states, due to short-range order. This study shows that the mechanism behind the phase transition in Fe2P-based materials is an isostructural transition that is equal for both first- and second-order transitions
Polaronic correlations and phonon renormalization in L a1-x S rxMn O3 (x=0.2, 0.3)
No full textAccording to standard theory the magnetoresistance magnitude in ferromagnetic manganites crucially depends on the electron-phonon coupling strength. We showed that in La0.7Sr0.3MnO3 the phonon renormalization is strong, despite its relatively small magnetoresistance. Here, we report results of a similar inelastic neutron-scattering investigation of a closely related compound, La0.8Sr0.2MnO3, where the magnetoresistance is enhanced. We find similar phonon renormalization and dynamic CE-type polaron correlations as in La0.7Sr0.3MnO3. However, quantitative comparison of the results for the two samples shows that only polaron lifetime is well correlated with the strength of the colossal magnetoresistance.RST/Fundamental Aspects of Materials and Energ
The economy of Dalmatia in Maschek’s “Manuals”
No full textU ovom radu autor prikazuje sedam svezaka “Priručnika” Luigia (Aloisa) Mascheka s gledišta ekonomske povijesti. Naime, pored ostaloga on u njima prikazuje razvitak gospodarstva Dalmacije kroz vjekove, ukazujući na njegove najznačajnije grane. Naravno, to se u prvom redu odnosi na poljodjelstvo kao zanimanje najvećeg dijela stanovništva pokrajine, a potom na pomorstvo i ribarstvo. Autor ovoga rada nastoji ukazati na Maschekovo posvemašnje prikazivanje raznih grana gospodarstva, sve vijesti koje se nalaze razasute po priručnicima, eda bi budućim istraživačima omogućio olakšati brži i učinkovitiji pristup tim podatcima. Pri tome postupa sustavno, prema načelima suvremene ekonomske povijesti. Na kraju prilaže neke statističke podatke crpljene iz tih priručnika, držeći ih vrijednima za upoznavanje prilika u Dalmaciji XIX. stoljeća.The author in the article reviews the seven volumes of Luigi (Aloiso) Maschek’s “Manuals” from the viewpoint of economic history. Namely, in addition to other things, Maschek in these volumes describes the development of the economy in Dalmatia through the centuries, pointing out its most important branches. Quite naturally, this first of all touches upon agriculture as the profession of the greatest number of the population in the province, followed by sailing and fishing. The author of the article makes an attempt to describe Maschek’s summary depiction of different branches of the economy, the news items that are scattered throughout the volumes in order to facilitate, make quicker and more effective the approach to this data for future scholars. He does this in a systematic fashion according to the principles of contemporary economic history. At the end of the article he records some statistical data derived from these manuals maintaining that it is of value for understanding the conditions in Dalmatia during the XIXth century
Tuning the magneto-elastic transition of (Mn,Fe,V)<sub>2</sub>(P,Si) alloys to low magnetic field applications
No full textThe first-order magneto-elastic transition in the Mn–Fe–P–Si alloys can be tailored by vanadium substitution. Alloys with a suitable V substitution provide an excellent magnetocaloric effect with minor hysteresis in low magnetic fields up to 1.2 T. Mössbauer measurements show that the hyperfine field is reduced by V substitution. Neutron diffraction reveals that Fe is substituted by V on the 3f site and the magnetic moment on the 3f site is enhanced by the V substitution. The modified magnetic exchange field around the 3f and 3g positions in the lattice can be utilized to design suitable magnetocaloric materials that operate in low magnetic fields.RST/Fundamental Aspects of Materials and EnergyRID/TS/Instrumenten groepQRD/Kouwenhoven LabRST/Neutron and Positron Methods in Material
Combined effect of annealing temperature and vanadium substitution for mangetocaloric Mn<sub>1.2-x</sub>V<sub>x</sub>Fe<sub>0.75</sub>P<sub>0.5</sub>Si<sub>0.5</sub> alloys
No full textApproaching the border of the first order transition and second order transition is significant to optimize the giant magnetocaloric materials performance. The influence of vanadium substitution in the Mn1.2-xVxFe0.75P0.5Si0.5 alloys is investigated for annealing temperatures of 1323, 1373 and 1423 K. By tuning both the annealing temperature and the V substitution simultaneously, the magnetocaloric effect can be enhanced without enlarging the thermal hysteresis near the border of the first to second order transition. Neutron diffraction measurements reveal the changes of site occupation and interatomic distances caused by varying the annealing temperature and V substitution. The properties of the alloy with x = 0.02 annealed at 1323 K is comparable to those found for the MnFe0.95P0.595Si0.33B0.075 alloy, illustrating that Mn1.2-xVxFe0.75P0.5Si0.5 alloys are excellent materials for magnetic heat-pumping near room temperature.</p
Reversible low-field magnetocaloric effect in Ni-Mn-In-based Heusler alloys
No full textNi-Mn-X (X = In, Sn, and Sb) based Heusler alloys show a strong potential for magnetic refrigeration owing to their large magnetocaloric effect (MCE) associated with first-order magnetostructural transition. However, the irreversibility of the MCE under low field change of 0–1 T directly hinders its application as an efficient magnetic coolant. In this work, we systematically investigate thermal and magnetic properties, crystalline structure and magnetocaloric performance in Ni51−xMn33.4In15.6Vx alloys. With the introduction of V, a stable magnetostructural transition near room temperature is observed between martensite and austenite. An extremely small hysteresis of 2.3 K is achieved for the composition x = 0.3. Due to this optimization, the magneticfield induced structural transition is partially reversible under 0–1 T cycles, resulting in a reversible MCE.Both magnetic and calorimetric measurements consistently show that the largest value for the reversible magnetic entropy change can reach about 5.1 J kg−1 K−1 in a field change of 0–1 T. A considerable and reversible adiabatic temperature change of −1.2 K by the direct measurement is also observed under a field change of 0–1.1 T. Furthermore, the origin of this small hysteresis is discussed. Based on the lattice parameters, the transformation stretch tensor is calculated, which indicates an improved geometric compatibility between the two phases. Our work greatly improves the MCE performance of Ni-Mn-X-based alloys and make them suitable as realistic magnetic refrigeration materials.<br/
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