Alloys In Magnetic Field Research Articles

Martensitic transformation in the systems based on Fe-Ni compositions in strong pulsed magnetic fields

Purpose of work. To ascertain the causes of the abnormally large displacement of the martensitic point in steels and iron alloys in strong pulsed magnetic fields at low temperatures. Research methods. Generalization of experimental and theoretical investigations of the strong magnetic field influence on the martensitic transformation in steels and iron alloys, taking into account the magnetic state of austenite. The obtained results. The distributions of the martensitic point displacement ΔMS from the content of the main component - iron and the temperature of the martensitic γ → α- transformation beginning (martensitic point MS) in different experiments are obtained. It is shown that the obtained temperature dependence ΔMS(MS) in a strong magnetic field at low temperatures decomposes into two components, one of which correlates with the generalized Clapeyron-Clausius equations, and the other is opposite to it. In addition, it was found that steels and alloys with intense γ → α- transformation in a magnetic field contain at least 72.5% iron (wt), which at low temperatures in the fcc structure is antiferromagnetic. Scientific novelty. The anomalous temperature dependence of the distribution ΔMS(MS) in a strong magnetic field is explained on the basis of quantum representations of the magnetic interaction of atoms in the Fe-Ni system. This effect is associated with a number of other invar effects, in particular, with an abnormally large spontaneous and forced magnetostriction, a strong dependence of the resulting exchange integral on the interatomic distance. The point of view according to which in these alloys in a magnetic field γ → α- transformation occurs by the type of “magnetic first kind phase transformation” is substantiated. It is assumed that the nucleation of the martensitic phase in a magnetic field occurs in (at) local regions of γ- phase with disoriented atomic magnetic moments (with high compression and increased forced magnetostriction). Practical value. The information obtained in this work provides grounds for explaining the kinetic features of the transformation of austenite into martensite in steels and iron alloys.

Microstructures and magnetic properties of cast alnico 8 permanent magnets under various heat treatment conditions

There is a close relationship between the magnetic properties of alnico permanent magnetic alloys and the nano-scaled spinodally decomposed structure which results from various heat treatment cycles. In this paper, different heat treatment cycles are employed to cast alnico 8 alloys with composition 32.3Fe-37.5Co-13.7Ni-6.2Al-5.8Ti-3.4Cu-0.2Zr-0.1S-0.8Nb. It is observed that magnetic field treatment at high temperature for specific time is the most effective method to obtain better microstructure and magnetic properties. The mosaic structures consisting of Fe-Co phase and Al-Ni rich phase are best separated during thermomagnetic treatment for 4–5 min and refined during low temperature treatments. The bias growth of the ferromagnetic phase does not develop in absence of magnetic field, and hence the phases are not refined and separated completely. This produces isotropic alnico alloys with low magnetic properties. However, continuous cooling of the alloys in magnetic field followed by isothermal treatment without magnetic field provides moderate magnetic properties. Treatment at high temperatures in field and without field for longer time leads to the coarsening of spinodal phases and poor magnetic properties. The optimum magnetic properties of Hcj = 1.7 kOe, Br = 8.0 kGs and (BH)max = 5.02 MGOe are attributed to the refined microstructure of the thermomagnetically treated alloys.

Experimental platform for solidification and in-situ magnetization measurement of undercooled melt under strong magnetic field.

An experimental platform for solidification of undercooled melt and synchronous measurement of magnetization under strong magnetic field is reported. The facility can be used for in-situ measurement of the magnetization of the undercooled melts and to studying the non-equilibrium solidification from deeply undercooled metals and alloys in magnetic field. The key advantages of this apparatus are first, we can obtain large undercooling in high fields by glass fluxing technique in combination with cyclical superheating and supercooling method, which is comparable to the maximum undercooling obtained by traditional method without magnetic field. Second, we can have a controlled thermal history with linear heating and cooling speed with high accuracy. Third, the temperature and magnetization measurement system are fast and on-line, which is very suitable for the investigation of both the structure transitions in the liquid in a wide temperature range (overheated and undercooled state) and the solid state phase transformations.

Phase transformations in Ni-Mn-In-based alloys in magnetic field

The effect of a high-strength magnetic field on the phase transformations of ferromagnetic materials based on the Ni-Mn-In system with different degrees of alloying has been revealed experimentally. The effect of the chemical composition of the alloys and magnetic treatment on the martensitic transformations and magnetic transitions has been investigated. It has been established that, upon substituting nickel atoms with manganese atoms, the temperature of the martensitic transformation decreases.

Effect of thermoelectric magnetic force on the array of dendrites during directional solidification of Al–Cu alloys in a high magnetic field

By eliminating the effect of the magnetic moment arising from the magnetic crystalline anisotropy, the effect of the thermoelectric magnetic force on the array of dendrites during directional solidification of Al–35 wt%Cu and Al-40 wt%Cu alloys in a high magnetic field has been investigated experimentally. The results indicate that the dendrite array is essentially destroyed, a result that could have general significance for understanding the processes involved in the solidification of alloys in a magnetic field.

Application of differential thermal analysis to investigation of magnetic field effect on solidification of Al–Cu hypereutectic alloy

Investigation of solidification in the Al–25 at.%Cu hypereutectic alloy in magnetic fields has been carried out by differential thermal analysis (DTA). The DTA results indicated that the nucleation temperatures of primary Al 2Cu phases and Al–Al 2Cu eutectics were lowered and the rates of crystal growth including primary phases and eutectics were reduced although the melting of the alloy was almost not affected in magnetic fields of 6 T and 12 T in comparison with those without a magnetic field. The suppression of nucleation and growth of primary phases and eutectics might be mainly attributed to reduction of diffusion rates of atoms in a magnetic field on the condition of suppression of convections. Primary Al 2Cu phases oriented along a magnetic field compared with disorder ones without a magnetic field, which was caused by the magnetic anisotropy.

Texturing hard Nd-Fe-B powdered ribbons in high magnetic field

A new route to texture NdFeB alloys in magnetic field was presented in a recent paper [1], constituting an attempt towards the preparation of anisotropic bonded magnets. NdFeB ribbons composed of Nd2Fe14B grains embedded in a Nd-Cu eutectic matrix, were annealed under an applied magnetic field up to 16T, at temperatures above the Nd-Cu melting temperature. A crystallographic texture was found to progressively develop at annealing temperatures, above 700 °C. In this paper, it is proposed that the grain orientation mechanism involves a competition between the aligning magnetic field torque acting on the magnetic grains and thermal disordering effects which becomes more and more significant as the temperature is increased. A simple model is developed to evaluate these effects. It is shown as well that a lowering of the alloy coercivity takes place during annealing.

Phase transformations in steels and alloys in magnetic field

Results obtained in studies of the effects of pulse and stationary magnetic fields on phase transformations in steels and alloys are reviewed. It is shown that a stationary magnetic filed produces a wider variety of effects on phase transformations is steels than a pulse magnetic filed.

Magnetic properties of the Ce 2Fe 17−xMn x helical magnets up to high magnetic fields

Magnetic properties of the Ce 2Fe 17− x Mn x , x=0–2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1< x⩽2 are helical ferromagnets or helical antiferromagnets at low and high T, respectively. Mn ions in the system carry average magnetic moment of 3.0±0.2 μ B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce 2Fe 17− x Mn x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce 2Fe 17− x Mn x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce 2Fe 17− x Mn x , x=0.5–2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated.

Mössbauer study of the invar Fe–Ni and Fe–Ni–C alloys in magnetic field

F.C.C. Fe-30.3%Ni and Fe-30.5%Ni-1.5%C (wt.%) alloys were studied by means of Mossbauer spectroscopy in external magnetic field B ext=2.5, 5, 7 T parallel to the gamma-beam. It is shown that distribution of effective magnetic field in the alloys is broad and that carbon expands the range of B eff. The external magnetic field increases B eff in the Fe-Ni alloy and decreases it more evidently in the Fe-Ni-C alloy. Antiferromagnetic spin coupling along the ferromagnetic component is proposed to explain data.

High-temperature oscillations of Bi andBi1−xSbxconductivity in high magnetic fields

Special quantum oscillations of conductivity in a magnetic field [``high-temperature'' oscillations (HTO)] are considered. The oscillations are periodic in the reciprocal magnetic field and are characterized by a frequency higher than that of Shubnikov--de Haas (SdH) oscillations. Results are presented of joint studies of SdH oscillations and HTO of the magnetoresistance for pure Bi and ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ (x=2.6 at. $%)$ alloy in magnetic fields up to 33 T. The oscillations are measured over the temperature range 4.3 to 30 K for a variety of magnetic field directions. The high field quantum limit is realized for different ratios of spectral parameters of electrons and holes in Bi and ${\mathrm{Bi}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}.$ In all cases the last HTO minimum coincides with the SdH oscillations corresponding to the quantum limit magnetic field. Analysis of the experimental data allowed selecting one of two alternative HTO models. The oscillations of conductivity result from electron-hole transitions between the Landau levels close to the Fermi level.

The behaviour of Ni-Mn-Ga martensitic alloys in magnetic field

Some of the Ni-Mn-Ga alloys exhibit a large shape change in magnetic field. This phenomenon occurs in their martensitic state and it is called the magnetic shape memory (MSM), since these materials can change their dimensions when the direction of the magnetic field varies. This kind of behaviour can be utilised in actuators and sensors. In the present work, three different polycrystalline Ni-Mn-Ga alloys are studied. The transformation temperatures together with the ferromagnetic Curie temperatures are determined by the magnetic susceptibility measurement and confirmed by the optical differential scanning calorimetry. The structures of the alloys are investigated with the optical microscopy and the X-ray 8-28-method. The sample behaviour in magnetic field is studied both by the vibrating sample magnetometer and by measuring magnetic-field-induced strain. Also, the effect of thermal, static and dynamic magneto-thermal cycling on the behaviour of the alloys in magnetic field is studied.

The effects of magnetic annealing of transition metal alloysdeduced from ab initio electronic structure calculations

A theory is presented for describing the effects of annealingmagnetic alloys in magnetic fields. It has an ab initiospin-polarized relativistic Korringa-Kohn-Rostokercoherent potential approximation (KKR-CPA) electronic structure basis anduses the framework of concentration waves. Alloys which wouldotherwise be soft magnets are found experimentally to developdirectional chemical order and significant uniaxial anisotropy whenannealed in magnetic fields. Our approach is able to provide aquantitative description of these effects together with theunderlying electronic mechanisms. We describe applications to thesoft magnetic alloys permalloy and FeCo.

Magnetization in Mn-richγ−Cu100−xMnx (36&lt;~x&lt;~83)alloys in fields up to 75 kOe

The field dependence of dc magnetization $[M(H)]$ has been measured in$\phantom{\rule{0ex}{0ex}}\ensuremath{\gamma}\ensuremath{-}{\mathrm{Cu}}_{100\ensuremath{-}x}{\mathrm{Mn}}_{x}$ ($x$=36, 60, 73, 76, and 83) alloys in magnetic fields up to 75 kOe at different temperatures between 4.2 and 21 K. The $M(H)$ data are found to be almost linear with field beyond 10 kOe. This is expected since the present alloys are antiferromagnetically ordered. But, at lower fields $(H&lt;10 \mathrm{kOe}),$ the variation is slower than linear. The change of slope in $M(H)$ beyond the critical field of 10 kOe is attributed to the spin-flop transition which marks the collapse of the helical spin structure and the onset of the linear spin-density-wave modulation. Another interesting observation is that the composition dependences of the magnetization and the electrical resistivity exhibit a minimum and a maximum, respectively, around $x=73$. This behavior is described in terms of the transition of magnetic structure from AF3 to AF1.

Magnetic field anisotropy of electron-impurity scattering in Al-Y alloys

In the present paper the results of studies of the deviations from Matthiessen's rule (DMRs) in single-crystal Al-Y alloys in magnetic fields up to 8 T are represented. The results obtained bear witness to the anisotropic behaviour of the mechanisms of conduction electron scattering from photons and impurity atoms. In the analysis of experimental data, a correlation was revealed between the behaviour of the temperature dependences of the DMRs and the direction of the magnetic field relative to the crystallographic orientation of the specimen, and an explanation of the negative value of the DMR observed in the experiment is given.

Low temperature resistivity anomaly in TiNb and TiV alloys

High precision measurements of the electrical resistivity (ϱ) of TiNb and TiV alloys in magnetic fields up to 23T revealed a slight enhancement of the resistivity (Δϱ) below T = 5–32 K. The temperature dependence and the magnetic field dependence of Δϱ depend on the magnitude of the resistivity pϱ Q T 0. The lnT dependence of Δϱ is observed in samples with ϱ O lower than about 110 μωcm, while the ≡T dependence is dominant in samples with ϱ O higher than it, where the negative magnetoresistance proportional to JH appears. These characteristics are roughly explained considering both the two-level-system and the weak localisation effect.

Magnetoresistance of PrxFe80−xB20 and HoxCo70−xB30 Amorphous Alloys in Magnetic Fields up to 22 T

physica status solidi (b)Volume 147, Issue 1 p. K47-K50 Short Note Magnetoresistance of PrxFe80−xB20 and HoxCo70−xB30 Amorphous Alloys in Magnetic Fields up to 22 T P. Czarnecki, P. Czarnecki Institute of Physics, A. Mickiewicz University, Poznań Search for more papers by this authorB. Idzikowski, B. Idzikowski Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this authorA. Wrzeciono, A. Wrzeciono Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this author P. Czarnecki, P. Czarnecki Institute of Physics, A. Mickiewicz University, Poznań Search for more papers by this authorB. Idzikowski, B. Idzikowski Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this authorA. Wrzeciono, A. Wrzeciono Institute of Molecular Physics, Polish Academy of Sciences, Poznań Search for more papers by this author First published: 1 May 1988 https://doi.org/10.1002/pssb.2221470161Citations: 3 Ul. Grunwaldzka 6, PL-60-780 Poznań, Poland. Ul. Smoluchowskiego 17/19, PL-60-179 Poznań, Poland. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume147, Issue11 May 1988Pages K47-K50 RelatedInformation

Transverse magnetoresistance of amorphous Fe40-xNi40CrxB20 alloys in magnetic fields up to 20 T

Transverse magnetoresistance of amorphous Fe40-xNi40CrxB20 alloys in magnetic fields up to 20 T

Field dependence of the Stoner factor in Pd-Ni alloys

The de Haas-van Alphen (DHVA) effect has been investigated in Pd and Pd-Ni alloys in magnetic fields extending to 40 T. With increasing Ni content, the incipient ferromagnetism gives rise to an unusual behaviour which is dominated by a field dependence of the Stoner factor.

Magnetoresistance of amorphous (FexNi100−x)80B10P10 alloys in magnetic fields up to 14.5 T

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