Showing papers on "Magnetic shape-memory alloy published in 2011"
TL;DR: The room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets, is demonstrated at room temperature.
Abstract: Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.
405 citations
TL;DR: In this article, a large exchange bias was observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state, which is related to the newly formed interface between different magnetic phases during the initial magnetization process.
Abstract: Exchange bias (EB) is usually observed in systems with an interface between different magnetic phases after field cooling. Here we report an unusual phenomenon in which a large EB can be observed in Ni-Mn-In bulk alloys after zero-field cooling from an unmagnetized state. We propose that this is related to the newly formed interface between different magnetic phases during the initial magnetization process. The magnetic unidirectional anisotropy, which is the origin of the EB effect, can be created isothermally below the blocking temperature.
278 citations
TL;DR: In this article, a new mechanism for superelasticity in oxygen-containing β-Ti-Nb alloys was proposed based on the results of in situ X-ray diffraction measurements and in situ TEM observations.
185 citations
TL;DR: In this paper, the authors analyzed the impact of a slight orthorhombic and monoclinic distortion of the Ni 50.2 Mn 28.3 Ga 21.5 at.
174 citations
TL;DR: Zr-Nb alloys consisting of α' or β phase have excellent mechanical properties with low magnetic susceptibility and, thus, these alloys could be useful for medical devices used in MRI.
138 citations
TL;DR: In this article, the results of neutron diffraction studies of the La0.70Sr0.30MnO2.85 compound and its behavior in an external magnetic field are stated.
Abstract: The results of neutron diffraction studies of the La0.70Sr0.30MnO2.85 compound and its behavior in an external magnetic field are stated. It is established that in the 4–300 K temperature range, two structural perovskite phases coexist in the sample, which differ in symmetry (groups $$R\bar 3c$$
and I4/mcm). The reason for the phase separation is the clustering of oxygen vacancies. The temperature (4–300 K) and field (0–140 kOe) dependences of the specific magnetic moment are measured. It is found that in zero external field, the magnetic state of La0.70Sr0.30MnO2.85 is a cluster spin glass, which is the result of frustration of Mn3+-O-Mn3+ exchange interactions. An increase in external magnetic field up to 10 kOe leads to fragmentation of ferromagnetic clusters and then to an increase in the degree of polarization of local spins of manganese and the emergence of long-range ferromagnetic order. With increasing magnetic field up to 140 kOe, the magnetic ordering temperature reaches 160 K. The causes of the structural and magnetic phase separation of this composition and formation mechanism of its spin-glass magnetic state are analyzed.
133 citations
TL;DR: The splat-quenched alloy showed a softer magnetic behavior as compared to the as-cast and aged alloys, and the aged alloy possessed a higher saturation magnetization and coercivity asCompared to theAs-cast alloy.
124 citations
TL;DR: The magnetic field triggers the changes of shape caused by either inducing the structural transition or rearranging the martensite variants as discussed by the authors, which is the best known functionalities of magnetic shape memory alloys.
Abstract: Publisher Summary The discovery of the ferromagnetic (FM) Heusler alloy Cu 2 MnAl, in the beginning of the twentieth century, made considerable impact in the field of magnetism. Although Cu 2 MnAl contained no FM element, it had a very high Curie temperature in excess of 600 K. Features related to the magnetostructural interplay in Heusler alloys are observed in the phonon and magnetization properties. This chapter discusses Heusler-based magnetic shape memory alloys. The complex behavior displayed by these materials is mainly a consequence of the strong coupling between magnetism and structure, which is driven by the martensitic transition. Magnetic shape memory properties are the best known functionalities shown by this class of materials. They refer to the ability of these alloys to show strong response in shape, strain, and dimensions to applied magnetic fields. The magnetic field triggers the changes of shape caused by either inducing the structural transition or rearranging the martensite variants. The first observation of the magnetic-field-controlled shape memory effect was made in Ni 2 MnGa. It is suggested that the mechanism giving rise to the large magnetostriction in Ni 2 MnGa consisted of a twin-related variant reorientation through field-induced twin-boundary motion.
120 citations
TL;DR: In this article, the dependence of magnetic anisotropy in CoFeB-MgO on the MgO layer thickness was investigated and it was shown that a clear perpendicular magnetic easy axis is obtainable in a 1.5-nm thick CoFe b layer by depositing Mg o of more than three monolayers.
Abstract: We investigated the dependence of perpendicular magnetic anisotropy in CoFeB-MgO on the MgO layer thickness. Magnetization curves show that a clear perpendicular magnetic easy axis is obtainable in a 1.5-nm thick CoFeB layer by depositing MgO of more than three monolayers. We investigated anisotropy in CoFeB-MgO deposited on four different buffer layers. Results show that a counter interface of CoFeB-nonmagnetic metal affects the perpendicular anisotropy of CoFeB/MgO.
117 citations
TL;DR: A giant exchange bias field of up to 1170 Oe was observed in the Mn2Ni1.6Sn 0.4 Heusler alloy as discussed by the authors, where a reentrant spin glass phase and a ferromagnetic martensitic phase coexist below the blocking temperature as confirmed by dc magnetization and ac susceptibility measurements.
Abstract: A giant exchange bias field of up to 1170 Oe was observed in the Mn2Ni1.6Sn0.4 Heusler alloy. A reentrant spin glass phase and a ferromagnetic martensitic phase coexist below the blocking temperature as confirmed by dc magnetization and ac susceptibility measurements. Exchange bias in Mn2Ni1.6Sn0.4 is thought to originate from the interface exchange interaction between the reentrant spin glass phase and the ferromagnetic martensitic phase. X-ray diffraction and selected area electron diffraction results demonstrate that excess Mn atoms occupy Ni and Sn sites randomly. In this way, Mn-Mn clusters are formed and constitute the reentrant-spin-glass phase.
100 citations
TL;DR: The temperature dependence of the specific magnetic moment of anion-deficient manganite La 0.70Sr 0.30MnO2 is measured in external magnetic fields of 0-140 kOe, with the prehistory taken into account.
Abstract: The temperature dependence of the specific magnetic moment of anion-deficient manganite La0.70Sr0.30MnO2.85 is measured in external magnetic fields of 0–140 kOe, with the prehistory taken into account. The inhomogeneous magnetic state is a cluster spin glass and is the result of a redistribution of oxygen vacancies. Increasing the external magnetic field initially (H < 10 kOe) leads to breakup of the ferromagnetic clusters, and then (H ≥ 10 kOe) to a transition of the antiferromagnetic matrix into a ferromagnetic state and an increase in the degree of polarization of the local manganese spins. The freezing temperature for the magnetic moments varies as Tf = 65–6H0.21, while the temperature at which the ZFC- and FC-curves diverge varies at Trev = 250–90H0.11. The cause of and mechanism for the magnetic phase separation are discussed.
Abstract: Fast magnetization precession is observed in L10-FePt alloy epitaxial thin films excited and detected by all-optical means. The precession frequency varies from 45 to 65 GHz depending on the applied magnetic field strength and direction, which can be explained by a uniform precession model taking account of first- and second-order uniaxial magnetic anisotropy. The lowest effective Gilbert damping constant has a minimum value of 0.055, which is about half that in Co/Pt multilayers and is comparable to Ni/Co multilayers with perpendicular magnetic anisotropy.
TL;DR: The magnetic susceptibilities of the α'-based Zr-Mo alloys are one-third those of Ti- 6Al-4V and Ti-6Al-7Nb, and thus these Zr alloy are useful for medical devices under MRI.
TL;DR: In this paper, high-field magnetic measurements were carried out in order to investigate behaviors of field-induced reverse martensitic transformation and kinetic arrest of NiCoMnSn metamagnetic shape memory alloy.
TL;DR: In this paper, an improved model of magnetic interaction between Mn atoms, which carry most of the localized magnetic moment of the alloys, was presented, which is supported by the exchange variation with the Mn-Mn distance and demonstrates excellent agreement between experimental and calculated magnetic moments.
Abstract: Recent studies have shown that the total magnetic moment in off-stoichiometric Ni–Mn–Ga alloys depends not only on electronic concentration but also on the degree of chemical order in the alloy. We have performed neutron diffraction experiments and magnetization measurements for determining the preferential atomic order and saturation moment in off-stoichiometric compounds (44–52 at.% Ni), having excess Mn and deficient in Ga. These alloys include isoelectronic alloys with different magnetic moments and were chosen in an effort to study the impact of chemical order on the magnetic moment distribution. In this work, we present an improved model of magnetic interaction between Mn atoms, which carry most of the localized magnetic moment of the alloys. The Mn atoms at Ga sites, which are nearest neighbors to properly sited Mn, couple antiferromagnetically to the dominant moment. In contrast, Mn atoms at Ga sites, which are nearest neighbors to Mn at Ni sites, couple ferromagnetically. Mn at Ni sites is always antiferromagnetic (AF). The new model is supported by the exchange variation with the Mn–Mn distance and demonstrates excellent agreement between experimental and calculated magnetic moments. The proposed model is shown to better explain the observed experimental results as compared to the rigid band model and previous localized moment models that assumed AF coupling for all off-site Mn atoms.
TL;DR: In this article, it was shown that in the GeTe/Sb2Te3 superlattice, an extraordinarily large magnetoresistance of ΔR/R 1/R 2/R 3 can be induced by application of an electrical field at temperatures exceeding 400 K.
Abstract: Phase-change GeTe/Sb2Te3 multilayered structures, in which the atomic motion at the layer interfaces is limited to one dimension, have been shown to require substantially lower switching energies when compared to monolithic alloys of the same average composition. Here, we report that in the GeTe/Sb2Te3 superlattice, an extraordinarily large magnetoresistance of ΔR/R > 2000% can be induced by application of an electrical field at temperatures exceeding 400 K. This finding paves the way for development of conceptually new memory devices that combine the merits of both phase-change and magnetic data storage.
TL;DR: In this article, a new physical-based magnetic/stress coupling model was proposed, where the effects of the applied magnetic field, elastic and plastic deformations on the magnetization were, respectively, considered in terms of different acting mechanisms.
Abstract: Traditional magnetic/stress coupling models are based on the magnetoelastic theory, which cannot explain magnetic phenomena when ferromagnetic materials are subjected to a plastic deformation. To promote the development of magnetomechanical theories, a new physical-based magnetic/stress coupling model was proposed in this paper, where the effects of the applied magnetic field, elastic and plastic deformations on the magnetization are, respectively, considered in terms of different acting mechanisms. Moreover, the influences of variants on the strength in different magnetization stages are also calculated.
15 Sep 2011-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the effects of Ta and Sn contents on the martensitic transformation temperature, crystal structure and thermal stability of Ti-Ta-Sn alloys were investigated in order to develop novel high temperature shape memory alloys.
Abstract: The effects of Ta and Sn contents on the martensitic transformation temperature, crystal structure and thermal stability of Ti–Ta–Sn alloys are investigated in order to develop novel high temperature shape memory alloys. The martensitic transformation temperature significantly decreases by aging or thermal cycling due to the formation of ω phase in the Ti–Ta binary alloys. The addition of Sn is effective for suppressing the formation of ω phase and improves stability of shape memory effect during thermal cycling. The amount of Sn content necessary for suppressing aging effect increases with decreasing Ta content. High martensitic transformation temperature with good thermal stability can be achieved by adjustment of the Ta and Sn contents. Furthermore, the addition of Sn as a substitute of Ta with keeping the transformation temperature same increases the transformation strain in the Ti–Ta–Sn alloys. A Ti–20Ta–3.5Sn alloy reveals stable shape memory effect with a martensitic transformation start temperature about 440 K and a larger recovery strain when compared with a Ti–Ta binary alloy showing similar martensitic transformation temperature.
TL;DR: The use of neutrons for the determination of magnetic structures has been a hot topic in the last 15 years as discussed by the authors, where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms.
Abstract: In 1949 Shull et al. [1] used for the first time neutrons for the determination of a magnetic structure. Ever since, the need for neutrons for the study of magnetism has increased. Two main reasons can be brought forward to explain this ongoing success: First of all a strong rise in research on functional materials (founding obliges) and secondly the increasing availability of easy to use programmes for the treatment of magnetic neutron diffraction data. The giant magnetoresistance effect, multiferroic materials, magnetoelasticity, magnetic shape memory alloys, magnetocaloric materials, high temperature superconductivity or spin polarized half metals: The last 15 years have seen the event of all these “hot topics” where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms. Refinement programs like FULLPROF or GSAS and programs for magnetic symmetry analysis like BASIREPS or SARAH make the determination of magnetic structures accessible for non specialists. Following a historical overview on the use of neutron powder diffraction for the determination of magnetic structures, I will try to convince you of the easiness of using magnetic symmetry analysis for the determination of magnetic structures using some recent examples of own research on the rare earth iron borate TbFe3(BO3)4 and the rare earth transition metal telluride Ho6FeTe2.
06 Jul 2011
TL;DR: In this article, the mechanical and magnetomechanical response of the Ni-Mn-Ga magnetic shape memory single crystals is discussed in detail and the importance of adjustment of the twin microstructure for obtaining an optimal actuating behavior is illustrated.
Abstract: Twinning stress or mechanical hysteresis associated with the twin boundary motion is one of the most essential parameters which determine the actuating performance of magnetic shape memory alloys. Recent effort at AdaptaMat Ltd. to decrease the twinning stress resulted in a consistent production of Ni-Mn-Ga magnetic shape memory single crystals with the twinning stress of about 0.1 MPa, which is much lower than previously reported. In this work, the mechanical and magnetomechanical response of the developed crystals is discussed in detail and the importance of adjustment of the twin microstructure for obtaining an optimal actuating behavior is illustrated.
TL;DR: The Fe85Si2B8P4Cu1 alloy has been newly developed in this article, which exhibits high saturation magnetic flux density (Bs) as well as good soft magnetic properties such as low coercivity, high effective permeability and low magnetostriction after nanocrystallization.
TL;DR: In this paper, the theory of thermomagnetic generation is reviewed and an efficiency analysis using experimentally measured magneto-thermal properties of 3d transitional and 4f rare earth ferromagnetic elements is presented.
Abstract: The theory of thermomagnetic generation is reviewed and an efficiency analysis using experimentally measured magneto-thermal properties of 3d transitional and 4f rare earth ferromagnetic elements is presented in this study. While theoretical results suggest that 55% of Carnot efficiency is possible, experimental data indicate values smaller than 25% of Carnot efficiency unless large magnetic field (e.g., Ha ∼ 80 kOe) is applied. For smaller magnetic fields representative of NdFeB permanent magnets (e.g., Ha = 3 kOe), the largest efficiencies are obtained for operating ferromagnetic materials over a smaller temperature difference (ΔT = 5 K). Furthermore, single crystal materials are found to have superior efficiencies, as do elements that undergo an order-to-order phase transition. Both of these later results relate to increased magnetization changes over a given ΔT. These results are subsequently used to postulate that a single domain structure will produce larger efficiencies due to the higher magnetization present over a wide range of magnetic fields when compared to multi-domain materials. Calculations for a Gd single domain suggest efficiencies on the order of 30% are possible, representing a threefold increase from multi-domain Gd at relatively small magnetic fields.
TL;DR: In this paper, the coexistence of superconductivity and ferromagnetism in Bi${}_{3}$Ni nanostructures that have been prepared by making use of novel chemical reaction paths was demonstrated.
Abstract: We demonstrate the coexistence of superconductivity and ferromagnetism in Bi${}_{3}$Ni nanostructures that have been prepared by making use of novel chemical-reaction paths. We have characterized their magnetic and superconducting properties by means of magnetometry and electrical-transport measurements. Other than in bulk geometry, submicrometer-sized particles and quasi-one-dimensional nanoscaled strains of single-phase Bi${}_{3}$Ni undergo ferromagnetic order. Superconductivity in confined Bi${}_{3}$Ni emerges in the ferromagnetically ordered phase and is stable up to remarkably high magnetic fields. Uniquely, ferromagnetic hysteresis at zero resistance is observed in nanostructured Bi${}_{3}$Ni.
TL;DR: In this article, it was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co.
Abstract: Magnetic measurements and neutron powder diffraction experiments on Ni50Mn33Sn17 and Ni45Co5Mn33Sn17 alloys were performed in order to establish the magnetic structures and the effects of Co substitution on the magnetic properties. It was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co. As a result of the change in the magnetic structure due to the Co substitution, the ferromagnetic properties of Ni–Co–Mn–Sn are enhanced. These results have enabled the concentration dependence of the magnetic moment to be quantified.
TL;DR: In this article, the electronic structures, the structural and magnetic properties related to shape memory applications for Mn2NiAl,Mn2NiGa,Mm2NiSn and Mn2NIn alloys were investigated using first principles density functional theory based method.
Abstract: Using first-principles density functional theory based method we have performed a systematic investigations of the electronic structures, the structural and magnetic properties related to shape memory applications for Mn2NiAl,Mn2NiGa,Mn2NiSn and Mn2NiIn alloys. Our results confirm that all the alloys undergo a volume conserving martensitic transformation at low temperatures and that the low temperature stable phase is a non-modulated tetragonal one. The relative stabilities of the martensitic phases and the magnetic properties differ considerably for Mn2NiAl, Mn2NiGa and Mn2NiIn and Mn2NiSn. Details of the electronic structures suggest that the differences in hybridizations between the magnetic components are responsible for these trends. Quantitative estimates of the energetics and the magnetizations indicate that Mn2NiGa and Mn2NiAl are more promising candidates for shape memory applications.
TL;DR: A new class of functional materials with giant nonhysteretic strain responses to applied fields is considered, and criteria for searching superresponsive two-phase nanostructured alloys are formulated.
Abstract: A new class of functional materials with giant nonhysteretic strain responses to applied fields is considered. They are decomposed two-phase systems consisting of single-domain nanoprecipitates of a low-symmetry phase. Their strain response is caused by the field-induced change of structural orientation of the domain states of these precipitates. The superresponse follows from the novel concept of structural anisotropy that is analogous to the magnetic anisotropy. Its vanishing produces a new glasslike structural state. The developed phase field theory and modeling allow us to formulate criteria for searching superresponsive two-phase nanostructured alloys.
TL;DR: In this article, the effects of the addition of Cu on the crystallization processes, nanostructures and soft magnetic properties for the Fe 80.8-84.2 alloys were investigated.
TL;DR: In this article, the magnetic behavior of CoFe 2 O 4 nanoparticles was investigated and it was shown that the magnetic properties of these nanoparticles are strongly dependent on the high temperature heat treatments that produce Co ions and vacancies disorder.
TL;DR: The structural and magnetic order are the decisive elements which vastly determine the properties of smart ternary intermetallics such as X2YZ Heusler alloys as discussed by the authors.
Abstract: The structural and magnetic order are the decisive elements which vastly determine the properties of smart ternary intermetallics such as X2YZ Heusler alloys. Here, X and Y are transition metal elements and Z is an element from the III-V group. In order to give a precise prescription of the possibilities to optimize the magnetic shape memory and magnetocaloric effects of these alloys, we use density functional theory calculations. In particular, we outline how one may find new intermetallics which show higher Curie and martensite transformation temperatures when compared with the prototypical magnetic shape-memory alloy Ni2MnGa. Higher operation temperatures are needed for technological applications at elevated temperatures.