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Thermal Strain And Magnetization Studies Of The Ferromagnetic Heusler Shape Memory Alloys Ni2mnga And The Effect Of Selective Substitution In 3d Elements On The Structural And Magnetic Phase
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Book Synopsis Thermal Strain and Magnetization Studies of the Ferromagnetic Heusler Shape Memory Alloys Ni2MnGa and the Effect of Selective Substitution in 3d Elements on the Structural and Magnetic Phase by : T. Sakon
Download or read book Thermal Strain and Magnetization Studies of the Ferromagnetic Heusler Shape Memory Alloys Ni2MnGa and the Effect of Selective Substitution in 3d Elements on the Structural and Magnetic Phase written by T. Sakon and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Thermal Strain and Magnetization Studies of the Ferromagnetic Heusler Shape Memory Alloys Ni2MnGa and the Effect of Selective Substitution in 3d Elements on the Structural and Magnetic Phase.
Book Synopsis Shape Memory Alloys by : Francisco Manuel Braz Fernandes
Download or read book Shape Memory Alloys written by Francisco Manuel Braz Fernandes and published by BoD – Books on Demand. This book was released on 2013-04-03 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: Shape memory alloys have become in the past decades a well established research subject. However, the complex relations between properties and structure have created a continuously growing interest for a deeper insight all this time. The complexity of relationships between structure and properties is mostly related to the fact that strong ?multidimensional? interactions are taking place: from the early studies focusing on the thermal and/or mechanical induced phase transformations to the more recent findings on the magnetically induced structural changes. On the other hand, these singular behavioral characteristics have driven a great industrial interest due to the innovative aspects that the applications of shape memory alloys may provide. This makes this subject a highly attractive source of continuous studies, ranging from basics crystallography and thermodynamics to mechanical analysis and electrical and magnetic properties characterization. In this book, a group of recent studies is compiled focusing on a wide range of topics from processing to the relationship between the structure and properties, as well as new applications.
Book Synopsis Magnetic Shape Memory Alloys by : Xuexi Zhang
Download or read book Magnetic Shape Memory Alloys written by Xuexi Zhang and published by Springer Nature. This book was released on 2021-11-14 with total page 273 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book systematically describes the fundamentals of Magnetic shape memory alloys (MSMAs), with an emphasis on low-dimensional structures such as foams, microwires and micro-particles. The respective chapters address basic concepts and theories, the fabrication of various architectures, microstructure tailoring, property optimization and cutting-edge applications. Taken together, they provide a clear understanding of the correlation between processing and the microstructural properties of MSMAs, which are illustrated in over two hundred figures and schematics. Given its scope and format, the book offers a valuable resource for a broad readership in various fields of materials science and engineering, especially for researchers, students and engineers.
Book Synopsis Advances in Magnetic Shape Memory Materials by : Volodymyr A. Chernenko
Download or read book Advances in Magnetic Shape Memory Materials written by Volodymyr A. Chernenko and published by Trans Tech Publications Ltd. This book was released on 2011-05-17 with total page 242 pages. Available in PDF, EPUB and Kindle. Book excerpt: Special topic volume with invited peer reviewed papers only.
Book Synopsis Ferromagnetic Shape Memory Alloys II by : Volodymyr A. Chernenko
Download or read book Ferromagnetic Shape Memory Alloys II written by Volodymyr A. Chernenko and published by Trans Tech Publications Ltd. This book was released on 2009-12-03 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume is indexed by Thomson Reuters CPCI-S (WoS). This work on Ferromagnetic Shape Memory Alloys contains selected peer-reviewed papers. Such materials belong to the most exciting and fastest-growing group of martensitic multifunctional materials. The selected papers cover the following topics of: Basic phenomena and theory; Structure and magnetic properties; Magnetomechanics and magnetocaloric effect; Thin films and composites; Modeling and simulations and Processing and engineering.
Book Synopsis Study on Phase Stability, Structural and Magnetic Properties of Ni-Mn-Ga Ferromagnetic Shape Memory Alloys by Ab Initio Calculations by : Nan Xu
Download or read book Study on Phase Stability, Structural and Magnetic Properties of Ni-Mn-Ga Ferromagnetic Shape Memory Alloys by Ab Initio Calculations written by Nan Xu and published by . This book was released on 2014 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) with chemical composition close to Ni2MnGa have received great attention due to their giant magnetic shape memory effect and fast dynamic response. In this work, a series of first-principles calculations have been performed within the framework of the Density Functional Theory (DFT) using the Vienna Ab initio Software Package (VASP). For the stoichiometric Ni2MnGa ferromagnetic shape memory alloy, the oscillation of Ni magnetic moment that depends on the atomic shuffling in the superstructure dominates the distribution of the total magnetic moment per Ni2MnGa unit. The structure change-associated total magnetic moment has been found to increase for Ni2MnGa unit from the cubic austenite to the tetragonal NM martensite through the monoclinic modulated martensites. For the off-stoichiometric Ni2MnGa ferromagnetic shape memory alloys, Ni-doping stabilizes the non-modulated martensite (NM) with simple tetragonal crystal structure, whereas proper Mn-doping stabilizes the seven-layered modulated (7M) martensite with monoclinic structure. Martensitic transformation experiences much larger driving force than that of the intermartensitic transformation. Moreover, the total magnetic moment of the three series of alloys is mainly dominated by their Mn content with little phase state dependence. The average Ni and Mn moments display both composition and phase state dependences. The perturbation of the magnetic moments by atom substitution is mainly located in the antisite and its close neighbors. It is mainly dominated by their Mn environment (distance and number). Insights into fundamental aspects such as phase stability and magnetic properties in Ni-Mn-Ga FSMAs are of great significance to improve the functional performances and to design new promising FSMAs.
Book Synopsis Ferromagnetic Shape Memory Alloys by : Lluis Manosa
Download or read book Ferromagnetic Shape Memory Alloys written by Lluis Manosa and published by Trans Tech Publications Ltd. This book was released on 2008-06-19 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: Volume is indexed by Thomson Reuters CPCI-S (WoS). Multiferroic shape-memory alloys that exhibit both ferroelastic and ferromagnetic properties have recently attracted much attention. They belong to the family of so-called smart materials and are future-generation materials that are likely to be useful in cutting-edge technologies. Apart from the theoretical challenge of understanding their fascinating properties, the quest to harness them for practical use is also attracting many scientists and engineers from all over the world.
Book Synopsis An Analysis of Ferromagnetic Shape Memory Alloys Produced by Melt Spinning, Sputtering and Pulsed Laser Deposition by : Neil Dearing
Download or read book An Analysis of Ferromagnetic Shape Memory Alloys Produced by Melt Spinning, Sputtering and Pulsed Laser Deposition written by Neil Dearing and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ferromagnetic shape memory alloys (FSMA) have recently attracted much interest and research because of their large magnetic-field induced strain. Strains of up to 10% have been reported in single crystals of Ni2MnGa at room temperature. The mechanism of twin boundary motion is understood to be responsible for the strain in FSMA?s and theoretically allows for a full crystal lattice distortion strain, which is 10% in the case of orthorhombic martensites and 5-6% in the case of tetragonal martensites. These strains however are only achievable in single crystals and much smaller strains have been observed in polycrystalline samples. Here, competition of the randomly orientated grains restrict the cooperative twin boundary motion that is evident in single crystals. Melt spun ribbons are often highly textured and may offer a method of producing ribbons in a form useful as a start material for applications, i.e. basis of a useful?bulk? compact form. Magnetic and structural properties of melt spun Ni-Mn-Ga have previously been reported. Applied magnetic field has been shown to affect the transformation strain on cooling. Ni-Mn-Ga alloys form a Heusler (L21) lattice which, on cooling, undergoes a diffusionless transformation beginning at the martensite start temperature Ms into either a tetragonal or orthorhombic martensite, both of which are highly twinned. The reverse transformation begins at the austenite start temperature As and both transformations occur over a range of approximately 10K. The type of martensite formed depends strongly on the composition of the sample and its thermal history. The influence of atomic order in Ni-Mn-Ga alloys has also been studied. It has been found that the degree of atomic order plays a large part in determining the martensitic transition temperature. This temperature is suppressed significantly in the disordered B2 structure where there is little correlation of the Mn and Ga atoms at the body center. Ni2MnGa undergoes a B2 to L21 (Heusler) transition at 1071K on cooling. In this work the structural and magnetic properties of melt spun Ni-Mn-Ga ribbons are presented and the effect of an applied magnetic field on the transformation strain is shown for the case of annealed ribbons under tensile stress. It is the intention of this work to explore the properties of melt-spun ribbons of the ferromagnetic shape memory alloys Ni-Mn-Ga and Ni-Fe-Ga with the addition of Tb. A range of compositions of both alloys have been created and analysed for both structural and magnetic properties. Melt spun ribbons are usually either amorphous or nanocrystalline, so the effect of heat treatments to both relieve stress and re-crystallise the ribbons is also explored. This provides some insight into how the crystal structure and magnetic properties evolve with annealing temperature. Thin films of these ferromagnetic shape memory alloys were also produced by both sputtering and pulsed laser deposition in order to characterise their behaviour and gain some insight into the growth conditions necessary to successfully produce thin films of ferromagnetic shape memory alloys. This was done because thin films grown at low temperatures can have similar properties to the melt spun ribbons, in that they are nanocrystalline or amorphous. It was hoped that producing and analysing these thin films would yield some more information about the behaviour of polycrystalline ferromagnetic shape memory alloys.
Book Synopsis Crystallography and Magnetism of Magnetocalorically Important Ni-Mn-X Based Heusler Alloys by : Amila S. B. Madiligama
Download or read book Crystallography and Magnetism of Magnetocalorically Important Ni-Mn-X Based Heusler Alloys written by Amila S. B. Madiligama and published by . This book was released on 2016 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ni-Mn-X Heusler alloys, demonstrating strong coupling between crystalline structure and magnetic state, were studied. They undergo field-induced, first-order transformations from a low symmetry martensite to a high-symmetry austenitic phase around room temperature. The substantial difference between the entropies of the two phases results in a large adiabatic temperature change, called "Giant Magnetocaloric Effect (GMCE)". Consequently, these alloys are promising refrigerants for near-room temperature cooling systems. This magnetic cooling is an energy-efficient and eco-friendly technology. Crystalline structures and magnetic states of these alloys, which determine their magnetocaloric performances, highly depend on their composition. To examine new paths to optimize their magnetocaloric performances, this research is focused on the crystalline and magnetic behavior of a series of alloys under various experimental conditions (one Ni-Mn-In, three Ni-Mn-In-Co and two Ni-Mn-Ga). Additionally, phase transformation temperatures, co-existing phases, site occupancies, the effects of a magnetic field on the phase transformation temperature and hysteresis were also studied. Their chemical compositions were determined by the RBS and EDS techniques. Rietveld refinements of diffraction data, reveals austenitic structure of all these alloys is cubic L21 (Fm3̅ m) and upon cooling, they transform into monoclinic martensitic phases (P 1 2/m 1 space group). Martensitic phase, except for Ni-Mn-Ga, is a mixture of two modulated monoclinic phases: either 5M & 7M or 6M & 8M. Ni-Mn-Ga alloys undergo inter-martensitic phase transformations from 7M modulated monoclinic phase to a non-modulated L10 tetragonal phase, upon cooling. Magnetic nature was determined by thermomagnetic, AC-susceptibility, and neutron diffraction. The austenitic phase of the Ni-Mn-In and Ni-Mn-In-Co alloys is ferromagnetic due to strong ferromagnetic interactions between Mn(4a-sites) and Mn(4b-sites). In the Ni-Mn-In-Co alloys, the interactions between Co atoms enhance the ferromagnetism of the austenite. The Ni- Mn-Ga alloys in the current study are paramagnetic in the austenitic phase and they order ferromagnetically in their martensitic phase. Magnetic interactions in the martensitic phase become complex with the variation of interatomic distances between magnetic atoms due to the modulations of the martensitic phase. Consequently, different magnetic natures, ferromagnetic, antiferromagnetic, and spin-glass-like are present in the martensitic phase. Both magnetic field and temperature drive the martensitic transformation. The hystereses associated with magnetic transformations are significantly higher than those of the crystalline transformations, and are approximately proportional to the square of the magnetic field. The hystereses associated with crystalline phase transformation have a minimum at a certain field. Because of the difference between the two transformations they merge only upon heating and under a certain magnetic field. In all studied martensitic transformations (i.e. upon cooling) the lattice entropy decreases. However, the effect is larger when the austenite's magnetic nature has higher entropy than the martensite does. Therefore, a magneto-structural transformation from antiferromagnetic martensite to cubic ferromagnetic austenite produces a large GMCE. However, it is vital to consider the thermal hysteresis losses associated with both phase transformations when calculating the GMCE.
Book Synopsis Magneto-thermo-mechanical Response and Magneto-caloric Effect in Magnetic Shape Memory Alloys by : Cengiz Yegin
Download or read book Magneto-thermo-mechanical Response and Magneto-caloric Effect in Magnetic Shape Memory Alloys written by Cengiz Yegin and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ni-Co-Mn-In system is a new type of magnetic shape memory alloys (MSMAs) where the first order structural and magnetic phase transitions overlap. These materials can generate large reversible shape changes due to magnetic-field-induced martensitic transformation, and exhibit magneto-caloric effect and magnetoresistance. Ni-Co-Mn-Sn alloys are inexpensive alternatives of the Ni-Co-Mn-In alloys. In both materials, austenite has higher magnetization levels than martensite. Fe-Mn-Ga is another MSMA system, however, whose magnetization trend is opposite to those of the Ni-Co-Mn-X (In-Sn) systems upon phase transformation. The MSMAs have attracted great interest in recent years, and their magnetic and thermo-mechanical properties need to be further investigated. In the present study, the effects of indium concentration, cooling, and annealing on martensitic transformation and magnetic response of single crystalline Ni-Co-Mn-In alloys were investigated. Increasing indium content reduced the martensitic transformation start (Ms) temperature, while increasing temperature hysteresis and saturation magnetization. Increasing annealing temperature led to an increase in the Ms temperature whereas annealing at 400 degrees C and 500 degrees C led to the kinetic arrest of austenite. Cooling after solution heat treatment also notably affected the transformation temperatures and magnetization response. While the transformation temperatures increased in the oil quenched samples compared to those in the water quenched samples, these temperatures decreased in furnace cooled samples due to the kinetic arrest. The possible reasons for the kinetic arrest are: atomic order changes, or precipitate formation. Shape memory and superelastic response, and magnetic field-induced shape recovery behavior of sintered Ni43Co7Mn39Sn11 polycrystalline alloys were also examined. The microstructural analysis showed the existence of small pores, which seem to increase the damage tolerance of the sintered polycrystalline samples. The recoverable transformation strain, irrecoverable strain and transformation temperature hysteresis increased with stress upon cooling under stress. Moreover, magnetic-field-induced strain due to the field-induced phase transformation was confirmed to be 0.6% at 319K. Almost perfect superelastic response was obtained at 343K. A magnetic entropy change of 22 J kg-1 K-1 were determined at 219K from magneto-caloric effect measurements which were conducted on annealed Ni43Co7Mn39Sn11 ribbons. Magnetic characteristics and martensitic transformation behavior of polycrystalline Fe-Mn-Ga alloys were also examined. Cast alloys at various compositions were undergone homogenization heat treatments. It was verified by magnetization measurements that the alloys heat treated at 1050 degrees C shows martensitic transformation. The heat treatment time was determined to be 1 day or 1 week depending on the compositions.
Book Synopsis Ferromagnetic Shape Memory Alloys by :
Download or read book Ferromagnetic Shape Memory Alloys written by and published by . This book was released on 2008 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: Multiferroic shape-memory alloys that exhibit both ferroelastic and ferromagnetic properties have recently attracted much attention. They belong to the family of so-called "smart materials" and are future-generation materials that are likely to be useful in cutting-edge technologies. Apart from the theoretical challenge of understanding their fascinating properties, the quest to harness them for practical use is also attracting many scientists and engineers from all over the world. This compilation comprises peer-reviewed papers, categorized into: I. Sample Preparation, II Thermal Treatments and Phase Stability, III. Magnetic and Structural characterization, IV. Microscopic studies of Magnetic Shape Memory Alloys, V. Effects of External Fields, VI. Coupled Effects: Magnetoresistance and Magnetocaloric effects. The volume thus provides a comprehensive introduction to this exciting new field.
Book Synopsis Shape Memory Response of Ni2mnga and Nimncoin Magnetic Shape Memory Alloys Under Compression by : Andrew Lee Brewer
Download or read book Shape Memory Response of Ni2mnga and Nimncoin Magnetic Shape Memory Alloys Under Compression written by Andrew Lee Brewer and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this study, the shape memory response of Ni2MnGa and NiMnCoIn magnetic shape memory alloys was observed under compressive stresses. Ni2MnGa is a magnetic shape memory alloy (MSMA) that has been shown to exhibit fully reversible, stressassisted magnetic field induced phase transformation (MFIPT) in the I X-phase transformation because of a large magnetostress of 7 MPa and small stress hysteresis. The X-phase is a recently discovered phase that is mechanically induced, however, the crystal structure is unknown. To better understand the transformation behavior of Ni2MnGa single crystal with [100] orientation, thermal cycling and pseudoelasticity tests were conducted with the goal of determining the Clausius-Clapeyron relationships for the various phase transformations. This information was then used to construct a stresstemperature phase diagram that illustrates the stress and temperature ranges where MFIPT is possible, as well as where the X-phase may be found. NiMnCoIn is a recently discovered meta-magnetic shape memory alloy (MMSMA) that exhibits unique magnetic properties. The ferromagnetic parent phase and the paramagnetic martensite phase allow the exploitation of the Zeeman energy. To gain a better understanding of the transformation behavior of NiMnCoIn, thermal cycling and pseudoelasticity tests were conducted on single crystals from two different batches with crystallographic orientations along the [100](011), [087], and [25 7 15] directions. A stress-temperature phase diagram was created that illustrates the Clausius- Clapeyron relationships for each orientation and batch. SQUID tests revealed the magnetic response of the alloy as well as the suppression of the martensite start temperature with increasing magnetic field. Pseudoelasticity experiments with and without magnetic field were conducted to experimentally quantify the magnetostress as a function of magnetic field. For the first time, it has been shown that NiMnCoIn is capable of exhibiting magnetostress levels of 18-36 MPa depending upon orientation, as well as nearly 6.5% transformation strain in the [100] direction. The results of this study reveal increased actuation stress levels in NiMnCoIn, which is the main limitation in most MSMAs. With this increased blocking stress, NiMnCoIn is a strong candidate for MFIPT.
Book Synopsis Development of Ni-Mn-based Ferromagnetic Shape Memory Alloys by : Chih-Kang Wu
Download or read book Development of Ni-Mn-based Ferromagnetic Shape Memory Alloys written by Chih-Kang Wu and published by . This book was released on 2011 with total page 146 pages. Available in PDF, EPUB and Kindle. Book excerpt: [Truncated abstract] Since the discovery of Ni2MnGa ferromagnetic shape memory alloys some 15 years ago, intensive research has been conducted to search and develop new and more powerful magnetically activated shape memory alloys. The effort has been severely hampered by the low magnetic driving force, intrinsically limited by the magnitude of magnetic crystallographic anisotropy, for mechanical actuation. The discovery of metamagnetic phase transformation in Ni-Mn-Z (Z=In,Sn,Sb) system in 2004, with their large magnetization difference across the transformation, made a breakthrough and brought new promise for creating magnetically activated shape memory alloys. This study is concerned with the development of Ni-Mn-Z (Z=In,Sn) ternary ferromagnetic martensitic alloys. Whereas having high promise owing to their large magnetization difference between their nonmagnetic martensite and ferromagnetic austenite, these alloys face the challenges of high mechanical resistance to deformation and brittleness. In response to these challenges, this study is focused on two main objectives: (1) to further enhance the magnetization difference of the metamagnetic reverse transformation of the alloys, and (2) to improve the toughness and ductility of the alloys, through alloying. (1) Enhance the Magnetization Difference New alloy design is accomplished in order to increase the magnetization difference between the austenitic and martensitic phases in Ni-Mn-Z (Z=In,Sn) alloys. The first step of the composition design is to maximise the use of Mn content to provide the potentially largest magnetization. Then, the proportion between Ni and In/Sn contents is adjusted to alter the chemical order for obtaining ferromagnetic structure. Lastly, Co addition is employed to modify the e/a ratio and to enhance the magnetic ordering of these alloys. In the new compositions of Mn50Ni40-xIn10Cox and Mn50Ni42-xSn8Cox alloys, a martensitic transformation from an Hg2CuTi-type austenite to body centred tetragonal martensite was observed...
Book Synopsis Ab-initio First Principle Modeling of Structural and Magnetic Phase Transformations in Co-Ni-Al Based Shape Memory Alloys by : Hassan S Thawabi
Download or read book Ab-initio First Principle Modeling of Structural and Magnetic Phase Transformations in Co-Ni-Al Based Shape Memory Alloys written by Hassan S Thawabi and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Ferromagnetic shape memory alloys FSMAs have diverse application, especially in the aerospace and bio-medical industries. They are a class of active and smart materials exhibiting strains under the influence of an applied magnetic field. These magnetic properties are mainly attributed to the martensitic structural phase trans- formation these material experience in response to temperature variation. Co-Ni-Al based alloys are one of the most promising ferromagnetic shape memory alloy FSMA that has been put recently under extensive study by researchers. They have shown extensive and promising features specifically those related to self-actuation. The effect of valence electron concentration and magnetic properties of Co-Ni-Al based ferromagnetic shape memory alloys on the martensitic transformations were analyzed utilizing Ab-initio first principle calculations. The variations of martensite start temperatures (Ms) and magnetic properties of a number of stoichiometric and mnon-stoichiometric Co-Ni-Al ferromagnetic shape memory alloys (FSMA's) with B2 austenite structure were studied and analyzed as a function of composition and lattice site ordering and site preference. A major conclusion of this thesis suggests that the magnetic valence number (Zm) should be considered in conjunction to the e/a ratio if the composition profile of the Ms is to be determined. Both Monte-Carlo and Ab-initio simulations were implemented to obtain the magnetic Heisenberg's exchange coupling parameters (J m) and model the magnetic transformations in stoichiometric Co2NiAl FSMAs. Two different cubic structures, ordered and disordered were compared to their tetragonal distortions martensitic phases and their Curie temperature (TC ) were obtained from the Monte-Carlo magnetic susceptibility temperature profile. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149454
Download or read book Heusler Alloys written by Claudia Felser and published by Springer. This book was released on 2015-11-12 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book gives an overview of the physics of Heusler compounds ranging from fundamental properties of these alloys to their applications. Especially Heusler compounds as half-metallic ferromagnetic and topological insulators are important in condensed matter science due to their potential in magnetism and as materials for energy conversion. The book is written by world-leaders in this field. It offers an ideal reference to researchers at any level.
Book Synopsis The Structure and Magnetic Properties of Ferromagnetic Shape Memory Alloys Containing Iron by : Amer Sheikh
Download or read book The Structure and Magnetic Properties of Ferromagnetic Shape Memory Alloys Containing Iron written by Amer Sheikh and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: An experimental investigation of the structural and magnetic properties of Iron basedferromagnetic shape memory alloys Pd57In25Fe18, Ti50Pd40Fe10, Ti50Pd35Fe15, FeMnSi, Fe66.7Mn26.8Si6.5 and Fe57.4Mn35Si7.6 is reported. Magnetisation measurements and highresolution powder neutron diffraction measurements were used to characterise the structuralproperties of each alloy. The parent phase of the Pd57In25Fe18 specimen has a FCC unit cell, space group Fm3m and lattice parameter a=6.293? 0.006?. The Fe atoms are essentiallyequally distributed on to the 4a and 4b sites with the Pd occupying the 8c site. On cooling thesample transforms into a tetragonal structure with I 4 / mmm space group and cell parametersa=4.097? 0.004? and c=7.289? 0.007?. Magnetisation measurements performed on thespecimen found Tc=140? 10K and a moment per formula unit of 1.39? 0.03?B. The inversesusceptibility has a Curie-Weiss variation, which yields a paramagnetic Curie temperature of159? 10K, an effective paramagnetic moment of 6.93? 0.06?B and a paramagnetic moment?pof 2.86? 0.03?B which is close to that generally observed for Fe on an FCC lattice. Neutrondiffraction measurements performed on Ti50Pd50-xFex compounds have confirmed the parentphase to be a cubic B2-type structure with the Pm3m space group with lattice parametersa=3.134? 0.007? when x=10 and a=3.118? 0.009? when x=15. On cooling, the martensiticphase transformation occurs and the alloys transform into an orthorhombic B19 structure(Pmma) with a 3-fold modulation. The lattice parameters were determined as a=13.853?0.001?, b=2.872? 0.001? and c=4.513? 0.002? when x=10 and a=13.465? 0.002?, b=2.923? 0.002? and c=4.526? 0.001? when x=15. The Curie temperature has been estimated usingthe Brillouin J=1 function as Tc~ 470? 10K when x=10 and Tc~523? 10K when x=15. For theFeMnSi specimen, the stoichiometry of alloys is consistent with that of C1b compounds. TheF 43m space group was employed for the cubic phase with a lattice parameter a=5.684?0.008?. On cooling the material transforms into a hexagonal martensite phase with 3 P6 /mcmIIspace group and lattice parameters, a=6.867? 0.001? and c=4.772? 0.002?. In theFe57.4Mn35Si7.6 compound there is no structural phase transition, the system orders in a FCC unitcell with space group Fm3m and lattice parameters a=3.616? 0.007?. In the Fe66.7Mn26.7Si6.5case at 500K the alloy orders in a FCC unit cell with space group Fm3m and latticeparameters a=3.611? 0.001?. On cooling, the material transforms into a HCP cell with thespace group 3 P6 / mmc and the lattice parameters a=2.540? 0.002? and c=4.108? 0.001?. Inthe FeMnSi alloy below 69K there is the onset of an incommensurate phase down to 5K, all theFe-Mn-Si based alloys order with a type-1 FCC antiferromagnetic structure. In the case ofFeMnSi, TN=69? 3K and for the Fe57.4Mn35Si7.6 and Fe66.7Mn26.8Si6.5 specimens TN has beenestimated using the Brillouin J=2 function, to be TN~389? 10K and 315? 10K respectively. From neutron measurements, at 5K a magnetic moment of 2.69? 0.04?B per site and 2.20?0.05?B per site was calculated for the Fe57.4Mn35Si7.6 and Fe66.7Mn26.8Si6.5 specimensrespectively.
Book Synopsis Magneto-Mechanical Response in Ni-Mn-Ga Magnetic Shape Memory Alloys by :
Download or read book Magneto-Mechanical Response in Ni-Mn-Ga Magnetic Shape Memory Alloys written by and published by . This book was released on 2004 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is generally accepted that the large reversible, magnetic-field-induced strain observed in ferromagnetic shape memory alloys is due to the rearrangement of twin variants in the martensite by an applied magnetic field leading to an overall change of shape. The main thermodynamic driving force for twin boundary motion in the presence of a magnetic field is the high magnetocrystalline anisotropy of the low-symmetry martensitic phase. Low twin boundary energy, high magnetocrystalline anisotropy energy and saturation magnetization are some of the key factors for large magnetic field induced strain. In order to achieve optimum performance, thermomechanical and magnetic treatments are necessary. In this investigation, a systematic investigation is being carried out on single crystals of Ni-Mn-Ga alloys to determine the combined effects of composition and thermomagneto-mechanical treatments on the crystal structure of the martensitic phases and the magnetomechanical properties of the Ni-Mn-Ga alloys. Repeated mechanical and magnetic forces have been applied to the samples. The results demonstrate that prior history has strong influence on the twinning start stress and twinning strain. In addition, heat treatment of the materials seems to increase the amount of strain that can be obtained (e.g. increased from 3% to 6%). Moreover, there is indication that prior heat treatment may also affect the martensite crystal structure that is formed during cooling. A systematic investigation has also been carried out to determine the effect of temperature on the magneto-mechanical behaviour of the Ni-Mn-Ga alloys. Strong temperature dependence of the magnetic shape memory effect in a Ni47.8Mn27.5Ga24.7 alloy has been observed.
