Showing papers on "Magnetic shape-memory alloy published in 1991"

Martensitic transformations in ultra-fine particles of metals and alloys

Abstract: Martensitic transformations in ultra-fine particles of Fe-Ni alloys, pure Co and Co-Fe alloys have been studied by X-ray diffraction and electron microscopy. The diameter of the particles used in the present work is 20–200 nm, three orders of magnitude smaller than that of the particles employed so far in studies of the martensitic transformation of ‘fine particles’. The composition range of Fe-Ni alloys is 12–35 at.% Ni and that of Co-Fe is 3–6 at.% Fe, and most of the particles are defect-free single crystals in the as-formed state. The most surprising finding is that the transformation below room temperature is very difficult to induce by simple cooling even in the case where particles of the parent phase contain lattice defects, while the transformation above room temperature occurs normally in most of the particles of Fe-Ni alloys and deformation at room temperature can easily induce the transformation. For pure Co and Co-Fe alloys, the transformation products above room temperature are 2H a...

Development of a shape memory alloy FeMnSi

Abstract: An austenitic shape memory alloy containing about 30 wt.% Mn and an appropriate amount of silicon has been developed. It is a cost-saving alloy and can be used for practical applications. When the strain is less than approximately 5%, the alloy exhibits a complete shape memory effect (SME) of one-way type. Contrary to most shape memory alloys which have ordered structures, the FeMnSi alloy without an ordered structure has a hysteresis as large as 500 K. SME of the alloy originates in the f.c.c.⇄h.c.p. martensitic transformation. The macroscopic properties and microscopic mechanisms involved in the martensitic transformation are reviewed.

Electronic and Magnetic Properties of Metals and Ceramics

Abstract: Magnetic Properties of Spinel Ferrites Electronic Properties of Liquid, Amorphous and Quasicrystalline Alloys Invar Alloys Magnetic Recording Materials Hydrogen in Pure Metals and Solid Solutions Ternary Hydrides Soft Magnetic Metals and Alloys Permanent Magnet Materials Magnetostrictive Materials High--Density Magneto--Optical Recording Materials

A magnetization model for computational magnetodynamics

Abstract: In order to calculate the magnetodynamic fields exactly, it is essential to work out a magnetization model. We have previously proposed a Chua‐type magnetization model based on magnetic domain theory. This Chua‐type model is now applied to typical ferromagnetic materials, such as iron, ferrite, and amorphous magnetic material. As a result, it is revealed that the typical magnetization characteristics of representative ferromagnetic materials can be satisfactory reproduced by our Chua‐type model.

Chapter 4 Magnetic amorphous alloys

Abstract: Summary The structural disorder of magnetic M-T, M-R and R-T alloys (T: magnetic transition metals, R: rare earths, M: not T and R) gives rise to significant changes of the mechanical, electrical, magnetic and magneto-optical properties as compared to the crystalline counterparts. Although it is not yet possible to explain many properties in terms of the relevant band structure of amorphous alloys, many new concepts and theories were generated and an overwhelming amount of experimental work was performed, leading to new physical insights concerning the atomic structure and short-range order, the relation between chemical bonding and magnetism, magnetic structures, anisotropic magnetic properties and transport properties on the one hand and the development of materials with a unique combination of properties on the other hand which makes these alloys attractive for a variety of applications. Generally, amorphous Fe-based alloys behave differently from Co- and Ni-based alloys due to their stronger (sp)-d hybridization and weaker covalent p-d bonding, resulting in broader valence bands. Also, they exhibit a sensitive dependence of the exchange coupling on the atomic distance, leading even to antiferromagnetic bonds for Fe Fe distances below 0.25 nm. The distribution of atomic distances inferred from the radial distribution function suggests the presence of a concentration-dependent portion of negative exchange interactions. Thus, various amorphous M 1 − x Fe x alloys show noncollinear magnetic structures, and for M = Zr, Hf, Y, La, Ce or Lu even speromagnetic or spin-glass-like behavior occurs with a tricritical point for x ≥ 0.9 and Curie temperatures ranging between 100 and 200 K. In amorphous M-Co alloys, small Co-Co distances are favorable for the magnetic moment formation and tend to increase the exchange interaction and thus T C . Therefore, amorphous Co-based alloys are predominantly strong ferromagnets, although significant differences in the magnetic properties are observed for Co-based alloys containing metalloids or other elements. The magnetic moment variation was interpreted in terms of the magnetic valence model or the environment model. In both cases, the experimental data were well described for certain classes of alloys. Most transition-metal-metalloid alloys exhibit good corrosion resistance, high electrical resistivity, good mechanical properties and are soft-magnetic materials. Ferich alloys exhibit the highest saturation flux density, and the Co-based alloys show low magnetostriction, high permeabilities and very low magnetic losses. These properties make various magnetic glasses attractive candidates for commercial applications such as power supplies, transformers, sensors, transducers, magnetic heads, magnetic shielding or magnetometers. Amorphous rare-earth-transition-metal alloys reveal pronounced differences in their magnetic properties as compared to M-T alloys due to the different electronic structure of the rare earths and the presence of two magnetic sublattices formed from elements of different groups. The negative exchange coupling between the 5d rare-earth electrons and the 3d transition-metal electrons leads to a parallel alignment of the R and T moments for the light rare earths and an antiparallel alignment for the heavy rare earths. A further difference in the amorphous R-T alloys with respect to M T alloys is the strong influence of the structural disorder on the local direction of the R moments which are coupled via the strong spin-orbit coupling to the randomly varying axes of the electrostatic field. This leads to sperimagnetic structures except for the Gd (S-state) based alloys exhibiting ferrimagnetic order. Amorphous R Fe and R Co alloys reveal the same differences as observed for M-Fe and M-Co alloys. Fe-rich R-Fe alloys exhibit a very low T C , below 200 K, due to competing positive and negative exchange interactions. Therefore, all R 1 − x Fe x alloys show a maximum in the concentration dependence of T C around x ≅ 0.7, followed by a strong turndown of T C at large x , in contrast to R-Co alloys revealing a steep increase of T C for alloy compositions with x above the critical composition. Amorphous R-T alloys containing non-S-state rare earths are characterized by strong uniaxial anisotropies and high coercivities but low magnetizations in the case of sperimagnetic order. The presence of a compensation temperature for the antiferro-magnetically coupled alloys gives rise to strong influences on the temperature and the concentration dependence of the magnetic, magneto-optical and transport properties. Amorphous R T alloys also show a large extraordinary Hall effect arising from side jumb and skew scattering processes. The favorable magnetic and magneto-optical properties have led to the development of GdTb-Fe, Tb-FeCo or Dy-FeCo alloys for magneto-optical data storage.

Well‐defined in‐plane uniaxial anisotropy in amorphous CoDyZr films

Abstract: The formation of in‐plane uniaxial anisotropy was investigated on amorphous CoDyZr films. The samples were prepared by rf sputtering in the presence of a magnetic field. We obtained films with a large and well‐defined in‐plane uniaxial anisotropy and without a perpendicular one if the perturbation of the plasma by the magnetic field was eliminated via the use of a sample holder having a special geometry, and if the sputtering was performed at pressures lower than a critical one. The results are discussed in terms of the change of the microstructure as a function of pressure.

The magnetic properties of sub‐20‐μm metallic fibers formed by continuous melt extraction

Abstract: Melt‐extraction technology has been developed which allows the continuous casting of fine metallic fibers down to less than 5 μm in diameter. Outstanding soft magnetic properties are found both for amorphous and crystalline alloys manufactured by this method. The technique will be discussed, as will the magnetic properties, both in ac and dc driving fields.

Magnetic properties of La(FexAl1-x)13 amorphous alloys

Abstract: Several kinds of La(FexAl1-x)13 (0.80

Magnetic phase transition and magnetocrystalline anisotropy of Sm2Fe17CxNy

Abstract: Alternating current (ac) susceptibility and high magnetic field measurements were performed to investigate the magnetic phase transitions and the magnetic anisotropy fields in Sm2Fe17CxNy with x=0, 0.4, 0.7, and 0.9. An unidentified magnetic phase transition is observed in all Sm2Fe17CxNy compounds, which is neither due to a spin reorientation nor due to a first‐order magnetization process (FOMP) transition. Samples of Sm2Fe17CxNy (x≳0) have even higher anisotropy fields than are found in Sm2Fe17Ny.

The First Order Magnetic Phase Transition in Dy-4%Y Alloy

Abstract: The first order magnetic transition of spiral to ferromagnetic structure of Dy-4%Y alloy, which is induced by both temperature and magnetic field, has been investigated by means of X-ray diffraction and magnetization measurement. The development of the ferromagnetic phase could be studied by X-ray diffraction measurement for the observation of the hexagonal to orthorohmbic crystal distortion accompanying the first order magnetic transition. Below T c , the ferromagnetic and spiral phases coexist down to 10 K and the latter was found to be in a meta-stable state. The development of the ferromagnetic phase induced by both temperature and magnetic field exhibits a time dependent behavior and is proportional to log t . The results are discussed with the one dimensional kink model assuming the “spin slip” in the spiral phase.

Magnetic alloy and method of production

Abstract: An anisotropic magnetic alloy having a columnar macrostructure is provided. The magnetic alloy is prepared by melting and casting an R-Fe-B alloy in order to make a magnetic alloy having a columnar macrostructure and heat treating the cast alloy at a temperature of greater than or equal to about 250° C. in order to magnetically harden the magnetic alloy. Alternatively, the cast alloy can be hot processed at a temperature greater than or equal to about 500° C. in order to align the axes of the crystal grains in a specific direction and make the magnetic alloy anisotropic. In another embodiment, the cast alloy can be hot processed at a temperature of greater than or equal to about 500° C. and then heat treated at a temperature of greater than or equal to about 250° C.

Studies of thermodynamic and magnetic properties of Ce1−xGdxSn3

Abstract: The temperature dependence of the specific heat, magnetic susceptibility, and 119Sn Mossbauer spectra of Ce1−xGdxSn3 has been measured. An evolution from mixed valent, to enhanced paramagnetic, to spin glass, and finally to a magnetically ordered state is observed as one alloys from pure CeSn3 to GdSn3. The C/T curves show a strong upswing at the lowest temperatures for the enhanced paramagnetic systems with dilute Gd concentrations. In the spin‐glass regime, the temperature where the cusp occurs in the zero‐field cooled magnetic susceptibility data is lower than the temperature at which the Mossbauer line width starts broadening. For the magnetically ordered state, TN increases with increasing Gd concentration reaching 31 K for pure GdSn3.

Effect of Magnetic Fields on Martensitic Transformations in Ferrous Alloys and Steels

Abstract: Recent works made by the authors' research group on magnetic field-induced martensitic transformations are reviewed, which are concerned with some ferrous alloys and steels. Main results of the works are as follows: The effect of magnetic fields on martensitic transformation start temperature is quantitatively explained by cumulative three energies, that is, magnetostatic energy, high field susceptibility energy and forced volume magnetostriction energy. Antiferromagnetic order in the parent phase suppresses the martensitic transformation. The appearance of magnetoelastic martensitic transformation is newly found in an ausaged Fe-Ni-Co-Ti alloy. Futhermore, directional growth of magnetic field-induced martensite plates is observed parallel to the magnetic field.

Anisotropy of grain‐oriented steel sheet under various elliptical field conditions

Abstract: We investigated the magnetic behavior of grain‐oriented steel sheet under various elliptical field conditions. The measurements show an additional anisotropy of the material properties depending on the direction of the elliptic rotation. We ascribe these phenomena to the different symmetries of the crystal anisotropy energy and of the ellipsoidal fields.

Temperature dependence of magnetovolume for Ni-Cr alloys near the critical composition for magnetism

Abstract: Measurements of the low-temperature thermal expansion coefficient, α, of Ni-Cr alloys close to the critical concentration, x c, for the ferromagnetic regime may be represented in the form α= A+BT+CT 3. The value for A increases in magnitude as x c is approached and abruptly changes sign at x c, being positive in the paramagnetic alloys and negative in the ferromagnetic alloys. Further measurements are reported that support a qualitative description proposed to account for the sign change in A, which is based upon a correspondence between the magnetovolume and the magnitude of the ordered magnetic moment and the moment fluctuation associated with the magnetic transition.

On the magnetism of Au4Ti, Au4V, Au4Cr, Au4Mn, Au8TiCr, and Au8VMn

Abstract: It is pointed out that the energy decrease due to the magnetization of the spin is large in the ferromagnetic substances and that the energy decrease due to the formation of the antiferromagnetic disposition is large in the antiferromagnetic substances. The calculation is made for the energy decrease in the ferromagnetic state as a function of the number of d electrons. This calculation explains the paramagnetic Au4Ti, the weak ferromagnetic Au4V, and the ferromagnetic Au4Mn. The energy decrease for Au5 and Au3V2 is also calculated, and it is shown that ferromagnetism appears in the vicinity of Au4V. The calculation is made for the energy decrease in the antiferromagnetic state as a function of the number of d electrons. This calculation suggests that antiferromagnetism appears in Au4Cr. The anisotropy energies for Au4V and Au4Mn are calculated to be in agreement with the experimental result. It is shown that the magnetic moment in Au4Cr should be parallel to [001] direction. Finally, the magnetism of Au8...

Magnetic properties of CoY amorphous alloys prepared by milling

Abstract: The crystal structures of YCo 5 and YCo 2 are transformed into a topologically random atomic arrangement by milling in an analogy with those of sputtered amorphous alloys. The magnetic state of YCo 2 is changed from paramagnetic to ferromagnetic, accompanying the change in the coordination number and in the atomic distance of CoCo from 6.0 and 2.55 A to 6.7 and 2.42 A, respectively. From X-ray diffraction studies and magnetic measurements, it is concluded that milled and sputtered amorphous alloys exhibit very similar structural and magnetic properties.

Magnetic clusters in melt-spun LaFe alloys

Abstract: La 100− x Fe x alloys ( x = 1,4,8) were produced with a melt-spinning method. The major component of the alloys was the f.c.c. β-La phase whose lattice constant is independent of the iron content and almost the same as that of the pure β-La phase. It was concluded from magnetization measurements and Mossbauer spectroscopy that small iron-rich magnetic clusters were formed. They interact ferromagnetically below 300 K and superparamagnetically between 300 and 400 K. The magnetic moment of 150 μ B was estimated to be a cluster magnetization from the temperature dependence of the inverse susceptibility. The temperature and magnetic field dependence of the magnetization was analyzed with a least-squares fitting based on a molecular-field theory.

Influence of hydrogen on magnetic properties of soft magnetic amorphous alloys

Abstract: The influence of electrolytic hydrogenation on the magnetic properties of three kinds of soft magnetic amorphous alloys with diffrent composition has been investigated. The experimental results showed that, after hydrogenation, the samples became very brittle and the soft magnetic properties of these alloys were seriously damaged, but the saturation magnetization and the average hyperfine field H_(bf) increased remakably. The experiments also showed that the hydrogen escaped gradually from the samples when they were left in air at room temperature and the magnetic and mechanical properties as well as the H_(hf) could recover gradually.

Reversibility of the Preferred Hyperfine Field Direction in the Electrochemically Deposited Fe–Ni–P Amorphous Alloys

Abstract: Electrochemically deposited Fe(–Ni)–P alloys exhibit in the as-deposited state a strong magnetic anisotropy with the easy axis perpendicular to the foil plane. Using 57Fe Moessbauer measurements in three transmission directions and an evaluation procedure modified with respect to that reported previonsly, it is shown that the Fe43Ni45P12 alloy indeed possesses a pronounced normal orientation of the hyperfine field, i.e. the spontaneous magnetization. Application of an in-plane external field leads to an alignment of magnetic domains in field direction, whereas remanent-state results agree with those in the as-deposited state.

Vapor‐deposition‐induced magnetic anisotropy in amorphous RE‐TM alloys (invited) (abstract)

Abstract: Macroscopic anisotropy may be induced in amorphous materials by either preparation or subsequent annealing under appropriate conditions. Large, macroscopic magnetic anisotropy is observed in amorphous rare earth–transition metal (a‐RE‐TM) alloys produced by vapor deposition. The vapor deposition process inherently contains characteristic directions about which an anisotropy can occur. These include the substrate, incident atomic beams, and magnetic or electric fields at the surface during growth. These intrinsic directions combine to produce effects such as columnar microstructure, stress and strains, pair ordering in alloys, and nonperpendicular film growth directions. All of these structural effects potentially can produce magnetic anisotropy. The presence of the localized nonspherical f‐electron nature of the RE ions causes a large local magnetic anisotropy; a macroscopic structural anisotropy can then cause a coherence in the directions of the local anisotropy axes, thereby producing a large macroscop...

The possible influence of crystal-like atom clusters on the magnetic properties of metallic glasses

Abstract: The magnetic anomaly of weak unidirectional magnetic anisotropy in (Co0.8Fe0.2)80B20 has been studied. The low-field magnetization loops are strongly perturbed in the presence of this type of magnetic anisotropy, This effect is more pronounced in metallic glasses obtained at high quenching rates. The author proposes that the magnetic anisotropy is caused by the presence of two magnetic phases with different local anisotropies and weak magnetic couplings. One of these-the amorphous matrix-would have a very small local magnetic anisotropy, while the other-clusters with nearly crystalline order-would have a high local magnetic anisotropy.

Magnetic field induced transitions in Pr2NiO4 single crystals

Abstract: Magnetization measurements in Pr2NiO4 single crystals were made up to 70kOe, for different orientations of the applied magnetic field with respect to the crystallographic axes, in the range from 1.5 to 300K. The Ni sublattice becomes antiferromagnetically ordered at TN=325K, as reported from previous neutron diffraction experiments1. There is also a structural transition at TC1=117K1, which allows a ferromagnetic component in the low temperature phase. Below TC1 different magnetic anomalies are observed, which have been interpreted as spin reorientations. Finally at low temperature the Pr sublattice is also ordered. Four different transitions induced by the external applied magnetic field parallel to the c-axis are visible in the range from 0 to 70 kOe, for T