Thickness dependence of magnetization in FeNi invar alloy film

The thickness dependence of magnetization of FeNi Invar alloy films was observed by means of small angle Lorentz electron diffraction. A remarkable reduction of magnetization at room temperature was observed for films with thickness below 400 Å. This may be ascribable to the instability of the ferromagnetic state in Fe-Ni Invar alloys.     

Mössbauer spectroscopy of Fe-Ni and Fe-Pt alloys

Mössbauer measurement on Fe-Ni and on Fe-Pt in the ordered and disordered states at various temperatures and in a longitudinal external field (H_ext = 50 kOe) have been analyzed. Hyperfine field distributions of Fe-Ni Invar alloys indicate that in addition to the ferromagnetic phase a second phase or state exists whose magnetic properties seem to be closely related to those of γ-Fe. No second phase or state was detected in the ordered Fe-Pt, while the situation in disordered Fe-Pt is uncertain.     

High-field susceptibility and magnetization in Fe-Ni invar alloys

The high-field susceptibility of Fe-Ni Invar alloys does not give rise to a sudden increase at the Curie temperature. The decrease in magnetization with increasing temperature is attributed to the T² term as well as to the spin wave term for Fe-Ni Invar alloys.     

Mössbauer effect study of the magnetic state of iron atoms in Fe-Ni 36 wt.% Invar alloys

The⁵⁷Fe Mössbauer spectra of the Fe-Ni 36 wt.% Invar alloy at different temperatures (300–530 K) have been measured. The experimental results indicate that the hyperfine field distributions are characterized by dual peaks. The temperature dependence of the hyperfine field indicates that some iron atoms may transfer from the ferromagnetic state to the antiferromagnetic one with increasing temperature, and that the variation of the ratio of numberN ₀ of the iron atoms in the antiferromagnetic state to the numberN _h in the ferromagnetic state with temperature will obey the thermodynamic relationship.     

The ΔE effect in iron-boron and iron-chromium-boron amorphous invar aloys

Temperature- and field-dependence of elastic properties of amorphous Fe-B and Fe-Cr-B Invar alloys have been investigated and Elinvar characteristics have been found together with a large ΔE effect. These results have been revealed that the elastic properties of these amorphous alloys are very different those of the crystalline Fe-Ni Invar alloy.     

Virtual miscibility gap and interdiffusion coefficient in iron-nickel invar alloys

Fe-Ni Invar alloys exhibit anomalies in thermodynamic and physical properties at high temperatures. This is considered to result from the tendency to two-phase separation in the fcc phase. This idea is supported also by interdiffusion experiments in the Fe-Ni system, where the interdiffusion coefficient is anomalously small in the Invar region at lower temperatures. A simple theory of regular solutions based on a pair interaction model is applied to the Fe-Ni system; with the assumption of two gamma states this gives a miscibility gap in the Invar region.     

Mössbauer study of local environment effects in the ordered Fe70Al30 Invar alloy: Temperature dependence of isomer shift in the spin-glass phase

The systematic studies of the magnetic hyperfine field distribution for ⁵⁷Fe in the spin-glass (SG) phase of the ordered Fe₇₀Al₃₀ Invar alloy have been performed using Mössbauer spectroscopy technique in the temperature range from 5 to 80 K. Particular emphasis has been placed on the low-field component of the distribution, which is considered as corresponding to the Fe sites in the SG magnetic configurations. The main result is the observation of the pronounced temperature dependence of isomer shift for several atomic SG configurations. The temperature behavior of the local electron density is strongly correlated to the Invar properties of the Fe₇₀Al₃₀ alloy. We argue that the observed temperature dependence of the isomer shift due to a local volume effect. The temperature range, for which the pronounced decrease in atomic volume is observed, coincides with the range of the existence of the Invar effect. The influence of the competition between opposite in sign exchange interactions on the Invar properties is discussed.     

Fe-Pt invar alloys—homogeneous strong ferromagnets

The thermal expansion and magnetic properties of Fe-Pt Invar alloys in both ordered and disordered states indicate that inhomogeneities play no essential role in determining large magnetovolume effects in Fe-Pt alloys. On the other hand, the concentration dependence of the magnetization, the hyperfine field at Fe nuclei and other related properties clearly show the strong ferromagnetism in Fe-Pt Invar alloys. Comparing the Invar behaviour found in Fe-Pt alloys with that in Fe-Ni alloys, it has been concluded that the so-called Invar effect generally consists of two types of anomalies. One is the essential effect, i.e., the large magnetovolume effect arising from the 3d band polarization and the other is the secondary or additional effect manifested as various magnetic anomalies associated with heterogeneities or weak ferromagnetism.     

Origin of the anomalies and thermodynamic aspects in iron-nickel invar alloys

The thermodynamic properties of Fe-Ni Invar alloys are analyzed in terms of the theoretical results obtained in the itinerant electron model accompanying in the mixing of the ferromagnetic and paramagnetic phases with different atomic volumes. All the anomalies in Fe-Ni Invar alloys are explained by the effect of a large magnetovolume coupling and this large coupling is attributed to the magnetic transformation due to the changes in temperature, magnetic field and pressure. There is also an enhancement due to the magnetovoume coupling to the high-field susceptibility, compressibility and forced magnetostriction. The pressure dependence of T_c is also discussed.     

Magnetic Transitions in Fe 3 Pt Invar Alloy Under High Pressure and Temperature Studied by Inelastic X-ray Scattering

The magnetic properties of the Invar alloy Fe 72 Pt 28 have been investigated by X-ray emission spectroscopy as a function of temperature up to 900 K and pressure up to 25 GPa. With increasing temperature and pressure, the amplitude of the Fe local moment, deduced from the Fe K g line satellite intensity, is reduced. Both the temperature and pressure dependence are interpreted in terms of transitions from a high-spin state to a low-spin state. This behavior provides a microscopic picture of the Fe magnetism in Invar alloys in agreement with the 2 n state model.     

Invar effects on some iron-base amorphous alloys

The thermal expansion and magnetic properties of Fe-B and Fe-P amorphous alloys prepared from melts have been investigated. These amorphous alloys show distinct Invar characteristics. heir magnetic properties are also very similar to those of Fe-Ni crystalline Invar alloys; that is, the high-field susceptability and forced-volume magnetostriction are remarkably large, the magnetic moment per Fe atom does not increase linearly, the Curie temperature decreases with a decrease in concentration of B or P, and their reduced their magnetization curves are much flatter than those of crystalline pure Fe.     

A vibronic state model of the invar problem

A new model is proposed to explain the Invar effect of Fe-Ni alloys and related problems, which an admixing of low and high spin states in vibrating Fe atoms and an itinerant electron ferromagnetism for the admixed state are taken into account.     

Invar effects of laves phase untermetallic compounds

The magnetovolume effects in Laves phase compounds such as AFe₂ and ACo₂ are received. In particular, Invar like behaviour which is found in (Zr_1-xNb_x)Fe₂ and Zr(Fe_1-xCo_x)₂ systems is reported. Comparing the present results with the classical Invar such as Fe-Ni and Fe-Pt alloys, it is proposed that so-called Invar anomalies should be classified into two type, i.e. the giant spontaneous volume magnetostriction, which is the essential characteristic of the Invar effect and the other anomalies which are observed in Fe-Ni and Zr(Fe_1-xCo_x)₂ systems but not in Fe-Pt and (Zr_1-xNb_x)Fe₂ systems.     

Low-temperature structure of Fe-Ni alloys

The Debye temperature (θ_M) of Fe-Ni alloys was obtained from measurements of the X-ray integrated intensity and the electrical resistivity at low temperatures from 4 to 300 K. A decrease of θ_M, implying a lattice softening effect, was found by lowering the temperature or increasing the iron concentration in the Invar region.     

First Observation of a Composition-Controlled Low-Moment/High-Moment Transition in the Fcc Fe-Ni System: Implications Regarding Invar and Anti-Invar Behaviors

We report the first direct observation of a high-moment (HM)/low-moment (LM) transition occurring in face centered cubic (FCC) Fe-Ni alloys. 57 Fe Mössbauer isomer shifts (ISs) give local electronic densities that exhibit a large discontinuity of , 0.4 el./ $ a_{0}^3 $ at the transition that spans the concentration range ～ 65-75 apc (atomic percent) Fe, in agreement with ab initio predictions. In the most Fe-rich alloys that have LM ground states (including n -Fe), we show that thermal stabilization of the HM state occurs at high temperatures, thereby providing an experimental proof that anti-Invar behavior is due to such HM stabilization. In Invar (Fe 65 Ni 35 ) and at near-Invar compositions, we observe temperature-induced changes in electronic density that follow the spontaneous magnetization curves and find that Invar is predominantly a HM phase at all temperatures where an Invar effect occurs. We show that LM phase thermal excitation cannot cause the Invar effect and that such excitation would cause a contraction instead of the required expansion, relative to normal behavior.     

Local moment model for the Invar effect

It has been shown by small-angle neutron scattering that the magnetic structure of Invar alloys in the ground state is characterized by the occurrence of static magnetic fluctuations on the scale of 10–12 Å. Centres of such fluctuations are iron atoms surrounded by the same sort of atoms in the nearest coordination sphere. These fluctuations are due to antiferromagnetic iron pair interactions. The magnetic part of thermal expansion coefficient of Fe-Ni alloys is evaluated within the framework of the molecular field approximation. The Invar effect is brought about by a mixed exchange interaction and by a strong dependence of the exchange integral J_FeFe on the interatomic distance.     

Temperature dependences of thermal expansion and saturation magnetization in Fe(67.0%)-Ni(32.5%)-Co(0.5%) Invar alloy with nanocrystalline structure

The effect of the nanocrystalline structure of Fe(67.0%)-Ni(32.5%)-Co(0.5%) Invar alloy on its thermal expansion is considered. It is found that the structure with grain mean sizes of about 100 nm increases its temperature coefficient of thermal expansion in the range of “invarness,” i.e., in the temperature range where the alloy offers the Invar properties. Reasons for this behavior are analyzed by taking the temperature dependence of the saturation magnetization.     

Invar合金的电子化学势均衡判据

用二元团簇作为描述Invar合金的基本结构单元,运用"团簇共振"结构模型,建立起以某一已知二元团簇与连接原子按1:x比例连接,描述Invar合金的电子化学势均衡判据.给出了Invar合金成分的经验分子式,即Invar合金成分=[团簇]1(连接原子)x.运用此判据,解析了部分Invar合金成分.发现典型的Invar合金实验成分与经验分子式相符合,说明基于"团簇共振"模型的Invar合金的电子化学势判据很好地解释了Invar合金成分的形成规律.     

Temperature dependence of forced volume magnetostriction in fcc Fe-Ni alloys

The forced volume magnetostriction of the fcc Fe-Ni Invar alloys has been measured in the temperature range from 77 to 900 K to elucidate the magnetovolume effect at finite temperatures. The temperature dependence of (θ ω/θ(H/M) is evaluated as well as (θ ω/θH), where ω is the volume expansion. These results are discussed using a phenomenological model for the magnetovolume effect which takes into account the contribution of the correlation between local magnetic moments.     

Evidence of new high-pressure magnetic phases in Fe–Pt Invar alloy

To investigate the magnetic properties of disordered Fe₇₀Pt₃₀ Invar alloy under high pressure, measurements of the real part of the AC susceptibility (χ) were made under pressure up to 7.5 GPa in the temperature range 4.2–385 K using a cubic anvil high-pressure apparatus. The Curie temperature (T_C) decreased with increasing pressure, and then, two new high-pressure magnetic phases appeared. These results show that the ferromagnetism of Fe–Pt Invar alloy becomes weaker, and the antiferromagnetic interaction becomes dominant with increasing pressure.