Effect of the addition of Ge to the FINEMET alloy

The results obtained by partially substituting Ge for B and Si in the FINEMET alloy for the purpose of improving its magnetic properties at high temperatures are presented in this work. Nanocrystalline ribbons were obtained from controlled crystallization of amorphous material made employing the melt spinning technique. The studied compositions were: Fe_73.5Si_13.5Ge₂Nb₃B₇Cu₁ and Fe_73.5Si_13.5Ge₄Nb₃B₅Cu₁. The structural evolution of these alloys was studied using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) and these results were correlated with their magnetic properties at different annealing temperatures. The coercivity obtained for both alloys was below 1 A/m at anneling temperatures between 773 and 823 K. The amorphous saturation magnetization was satisfactory, almost 137 emu/g, comparable with that obtained for FINEMET alloys. The nanocrystallization and the Curie temperatures are dependent on Ge concentration.     

Structural relaxation,crystallization and improvement of magnetic properties in FeXSiB (X=Cr,Nb)-type amorphous alloys

In the present paper, the influence of Nb and Cr on intensity of structural relaxation, crystallization processes, electric and magnetic properties in the Fe₇₆Nb₂Si₁₃B₉, Fe₇₆Cr₂Si₁₃B₉ and Fe₇₆Nb₁Cr₁Si₁₃B₉ alloys were investigated. It was shown that the improvement of magnetic permeability caused by a suitable annealing is a thermally activated process. Activation energy of this process is found to be of the order of 1 eV. Cr as an alloying addition to the Fe–Si–B alloy does not change the 1 h optimization annealing temperature and causes an increase of its efficiency. Nb as an alloying addition causes an increase of the 1 h optimization annealing temperature, and also the temperature of the first step of crystallization.     

Structural and magnetic study of bulk glassy Fe72 − x Co x B20Si4Nb4 alloys

The influence of the partial replacement of Fe by Co on the structural and magnetic properties of bulk-type glassy Fe_72???x Co _x B₂₀Si₄Nb₄ (x = 0, 5, 10, 15, 20, 25, 30, 35) alloys has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD) magnetic measurements and Mössbauer spectroscopy. Results show that the successive Co addition: (1) does not affect the mass density of the studied alloys, (2) affects appreciably the super cooled region, (3) modifies the magnetic properties, exhibiting soft magnetic behavior, (4) modifies the spin texture and disorder within the studied specimens.     

Nanocrystals magnetic contribution to FINEMET-type soft magnetic materials with Ge addition

Over the last years several works have been published in which magnetic and structural properties of soft magnetic nanocrystalline alloys were reported. Among these, there are a series of articles where the nanocrystals composition of FINEMET-type alloys with Ge addition was obtained by Mössbauer spectroscopy (MS) and X-ray diffraction (XRD). By considering a linear relationship between the magnetic moments of the nanocrystals and the composition of various elements in these crystallites, the magnetic moment of the nanocrystals was calculated. This paper reviews results obtained by different authors since 1980 and they are compared with ours. In turn, we revised some elements not previously considered for the calculus of the nanocrystals composition that allowed us to obtain the magnetic moment of the crystallites in the alloy. In particular, we analyzed FINEMET-type alloys with replacement of B for Ge: Fe_73.5Si_13.5Ge₂B₇Nb₃Cu₁ and Fe_73.5Si_13.5Ge₄B₅Nb₃Cu₁. The nanocrystalline structure was obtained by isothermal annealing of melt-spun ribbons at 823 K for 1 h. From MS and XRD we obtained the atomic composition of the nanocrystals in the magnetic material. The magnetic contribution of the nanocrystals to the alloy was calculated using a linear model and the results were compared with experimental measurements of the samples.     

Effect of thermal treatment on the magnetization processes of nanocrystalline Fe80Ge3Nb10B7 alloys

The dynamic magnetization processes of nanocrystalline Fe₈₀Ge₃Nb₁₀B₇ alloys after annealing at different temperatures are studied through the permeability spectroscopy. Three steps of crystallization are found when amorphous Fe₈₀Ge₃Nb₁₀B₇ alloys are heated from 300to 1200 K. The dominant magnetization process varies with different annealing temperatures. Domain wall bulging is the main magnetization mechanism under weak applied field. When the applied field exceeds pinning field H_p, the depinning-involved domain wall displacement occurs. Different annealing temperature results in different H_p. The lower value of μ′ and high relaxation frequency after heating at 923 and 973 K are due to the strengthened domain wall pinning and the increase of magnetocrystalline anisotropy.     

Effect of crystallization annealing under loading on the magnetic properties and the structure of a soft magnetic FeSiNbCuB alloy doped with chromium

The changes of quasi-static magnetic hysteresis loops and X-ray diffraction patterns of the Fe_73.5Si_13.5B₉Nb₃Cu₁ doped to 10 at % chromium instead of iron have been studied to elucidate the influence of the thermomechanical treatment consisting of annealing and cooling of the alloy under the tensile stress (tensile-stress annealing (TSA)) on the magnetic properties and the structure of these alloys. It is shown that the treatment results in the induction of the magnetic anisotropy of the hard axis type at which the magnetization reversal along the direction of applying the external stress during annealing is hampered. The energy of the induced magnetic anisotropy decreases as the chromium content increases. During TSA, the nanocrystal lattices are deformed, and the deformation is retained after cooling. The interplanar spacings increase along the extension direction and decrease in the transverse direction. The deformation anisotropy is observed for crystallographic directions. The anisotropic deformation of the bcc lattice of nanocrystals with high content of the ordered Fe₃Si phase characterized by a negative magnetoelastic interaction is the cause of formation of the state with the transverse magnetic anisotropy of the hard axis type.     

Long-term stability of soft magnetic properties of amorphous and nanocrystalline alloys based on iron

In the present paper long-term stability of magnetic properties of different amorphous and nanocrystalline alloys was studied. Magnetic properties were measured for annealed samples (300<Ta<900 K) directly after annealing and after long-term aging at room temperature. It was shown that for the Fe_75.3Cu₁Zr_1.7Si₁₃B₉ alloy magnetic permeability of the optimized samples is stable during 8 years aging. For Fe_86−xNb_xB₁₄ alloys the observed long-term instability (3 years aging) is due to annealing out of free volume leading to formations of small iron clusters coherent with the amorphous surroundings.     

Effect of cooling rate in [(Fe0.5Co0.5)0.75B0.2Si0.05]100-xNbx alloy system on magnetic properties

The effect of cooling rate on the thermal stability and soft magnetic properties of [(Fe_0.5Co_0.5)_0.75B_0.2Si_0.05]_100-xNb_x (x = 5, 6, 7, 8 at. %) system was investigated. The alloys were produced into the form of ribbon and cylindrical rod by melt-spinning and injection casting, respectively. Their structure, thermal, mechanical and soft magnetic properties were investigated by x-ray diffraction, differential scanning calorimetry, universal testing machine and vibrating sample magnetometer, respectively. All of the alloys were identified as fully amorphous by X-ray diffraction. It turned out that the rod samples had exceptionally high saturation fields reaching 3.0 kOe, which is key properties for sensor application. Also, among these Fe,Co-based samples, the Fe_35.25 Co_35.25 B_18.8 Si_4.70 Nb₆ ribbon exhibits the highest saturation magnetization with 142.1 emu/g.     

Thermomagnetic study of nanophases in Fe-based soft magnetic materials

The Curie temperatures (T_c) of metastable nanophases have been investigated in partially crystallized Fe_73.5Cu₁Nb₃Si_13.5B₉ and Fe₈₆Zr₇Cu₁B₆ nanostructured soft magnetic alloys as a function of annealing temperature and time. It is shown that for both materials a supersaturated phase is formed which transforms only at the second stage of crystallization by dissolution of the solute elements monitored by the steep increase of T_c.     

Annealing effect on soft magnetic properties and magnetoimpedance of Finemet Fe73.5Si13.5B9Nb3Au1 alloy

Effect of annealing on the soft magnetic properties of Fe_73.5Si_13.5B₉Nb₃Au₁ amorphous ribbon has been investigated by means of structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 °C for 30, 60, 90 min, soft magnetic properties have been improved drastically. Among the samples investigated, the sample annealed at 530 °C for 90 min showed the softest magnetic behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing.     

Investigation of X-ray diffraction and positron life times in Fe78Si9B13 alloys of amorphous and crystalline structures before and after hydriding

Measurements of mean positron life-times and X-ray diffraction were carried out in unhydrided alloys Fe₇₈Si₉B₁₃ of amorphous and crystalline structures, and after hydriding them. The process of hydriding was carried out at a pressure of 55.773 × 10⁵ N/m². during 168 h. The crystalline samples were obtained after annealing the amorphous alloy Fe₇₈Si₉B₁₃ at 673, 773 and 873 K, respectively. The results obtained after the hydriding process suggest thatan additional electron energy band is formed due to introducing hydrogen inside the samples. The annealing process shows that there exists a nonmonotonic relation between the concentration of free electrons and the degree of order to the structure.     

Coercivity and induced magnetic anisotropy by stress and/or field annealing in Fe- and Co- based (Finemet-type) amorphous alloys

Uniaxial magnetic anisotropy has been induced in amorphous Fe_73.5Cu₁Nb₃Si_15.5B₇ (Fe-rich) and (Co₇₇Si_13.5B_9.5)₉₀Fe₇Nb₃ (Co-rich) ferromagnetic alloys by annealing under stress and/or magnetic field. Such anisotropy plays a crucial role on the magnetization process and, consequently, determine the future applications of these materials. The mechanisms involved on the origin of such induced magnetic anisotropy showed significant differences between Fe-rich and Co-rich amorphous alloys. This work provides a comparative study of the coercive field and induced magnetic anisotropy in Fe-rich and Co-rich (Finemet) amorphous alloys treated by stress and/or field.     

Induced magnetic anisotropy in Co-doped Finemet-type nanocrystalline materials

Transverse magnetic anisotropy has been induced in the Fe_14.7Co_58.8Cu₁Nb₃Si_13.5B₉ and Fe_13.8Co₆₅Cu_0.6Nb_2.6Si₉B₉ amorphous ribbons by annealing under an external magnetic field. This anisotropy plays a predominant role, compared to magneto-crystalline and magneto-elastic anisotropies, in forming the magnetic properties and shaping the hysteresis loop. The effect of temperature and time of annealing on the induced magnetic anisotropy and magnetic properties (magnetic permeability, coercivity and power losses) in both alloys was investigated. Under this work, measurements of frequency dependence of the real and imaginary parts of magnetic permeability were made within a frequency range up to 110 MHz. It was found that as a result of magnetic field annealing the Snoek limit increases in both alloys compared to the Co-free Finemet.     

Effect of Cu additions on the magnetic properties and microstructure of FeCoNbB nanocrystalline alloy

The influence of Cu content and the annealing conditions in the (Fe_0.5Co_0.5)_85?x Nb₇B₈Cu _x (x=0.5, 1.0, 1.5) soft magnetic alloys on the magnetic properties and microstructure were investigated. The additions of Cu lower the primary and secondary crystallization temperatures and the α→γ phase transformation temperature of the FeCoNbB alloys. The (Fe_0.5Co_0.5)₈₄Nb₇B₈Cu₁ alloy annealed at 873 K for 3.6 ks, in which α-(Fe, Co) nanocrystalline phase with diameter of 5 nm precipitated from the amorphous matrix, shows the best soft magnetic properties. The resulting (Fe_0.5Co_0.5)₈₄Nb₇B₈Cu₁ nanocrystalline alloy exhibits a high saturation flux density of 1.88 T, low coercivity of 42 A/m, very high Curie temperature of 1240 K, as well as low core loss of 770 W/kg at 10 kHz under maximum magnetization of 1 T.     

Nanocrystallization process and ferromagnetic properties of amorphous (Fe0.99Mo0.01)78Si9B13 ribbons

The nanocrystallization process of soft ferromagnetic (Fe_0.99Mo_0.01)₇₈Si₉B₁₃ ribbons has been studied in detail. Microstructural and ferromagnetic properties are examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), Mössbauer spectroscopy (MS), differential scanning calorimetry (DSC) and magnetization measurements. The Curie and crystallization temperatures are determined to be T_C=665 K and T_x=750 K, respectively. The T_x value is in well agreement with DSC measurement results. XRD patterns had shown two metastable phases (Fe₂₃B₆, Fe₃B) which were formed under in situ nanocrystallization process. These metastable phases embedded in the amorphous matrix have a significant effect on magnetic ordering. The ultimate nanocrystalline (NC) phases of α-Fe(Mo, Si) and Fe₂B at optimum annealing temperature had been observed respectively. It is notable that the magnetization of the amorphous phase decreases more rapidly with increasing temperature than those of NC ferromagnetism, which suggest the presence of the distribution of exchange interaction in the amorphous phase or high metalloid contents.     

Magnetic properties and temperature stability of a molybdenum-doped finemet-type alloy

The influence of nanocrystallization conditions on the structure, magnetic properties, and temperature stability of nanocrystalline magnetically soft Fe_73.5Cu₁Nb_1.5Mo_1.5Si_13.5B₉ alloy is studied. It is found that preliminary low-temperature annealing exerts an influence on subsequent nanocrystallization of the alloy. In addition, preannealing followed by nanocrystallization considerably improves the magnetic properties of the alloy. It is shown that the magnetic properties of the material can be controlled by varying the frequency of a magnetic field used for thermal treatment causing nanocrystallization. It is established that the magnetic properties of nanocrystalline Fe_73.5Cu₁Nb_1.5Mo_1.5Si_13.5B₉ alloy offer a high temperature stability.     

Rapid stress annealing dependence of structural and magnetic properties of Fe75 − x Co x Cu1Nb3Si15B6 alloys

Structural and magnetic properties of nanocrystalline Fe_75???x Co _x Cu₁ Nb₃Si₁₅B₆ (x?=?0, 2, 5) alloys are reported using magnetic measurements X-ray diffraction, Mössbauer spectroscopy. Results show that: (1) for the specimens with x?=?0 reveal that the volume fraction of the nanograins and their grain diameter ranges between 56% and 80% and 10 and 18 nm, (2) annealing above 700°C apart from Fe₃Si type nanocrystals, magnetically hard Fe₃B, Fe₂₃B phases also appear, leading to a sharp increase of the coercive field, (3) Co content and applied stress during annealing has considerable effect on relative permeability and stress induced anisotropy, which is perpendicular to the ribbon axis, Mössbauer spectroscopy also suggests changes in spin texture.     

57Fe Mössbauer study of amorphous Fe81B13.5Si3.5C2

The amorphous ferromagnet Fe₈₁B_13.5Si_3.5C₂ (Metglas^® 2605SC) has been investigated with Mössbauer spectroscopy. The hyperfine interaction parameters are studied between 80 and 300 K from which some characteristic properties are deduced. The behaviour of the amorphous alloy at higher temperatures has been studied by the room temperature spectra of annealed samples. After a structural relaxation process, a two step crystallization transformation is observed leading to Fe-Si alloy and Fe₂(B, C). X-ray diffraction of samples annealed at higher temperatures reveals the presence of an orthorhombic Fe-B-Si phase of which the structure changes slightly with annealing temperature.     

A potential Co36Fe36Si4B20Nb4 nanocrystalline alloy for high temperature soft magnetic applications

The paper addresses the structural, crystallization, soft magnetic and Curie temperature behaviour of Co₃₆Fe₃₆Si₄B₂₀Nb₄ alloy. The material, prepared in the form of ribbons by melt-spinning technique, was amorphous in the as-cast state. Differential scanning calorimetry (DSC) showed two stages of crystallization whereas thermal variation of electrical resistivity (TER) carried out to a higher range of temperature indicated three stages of crystallization. The first crystallization stage, which occurred at 845?K and 825?K in DSC and TER, respectively, was due to the formation of nanophase (CoFe)₂Si as evidenced by X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The formation of these nanoparticles reduced the magnetocrystalline anisotropy, thereby revealing good soft magnetic properties in the samples annealed between 825?K and 875?K with coercivity less than 49.9?A?m^?1 (627?mOe) and susceptibility?～?0.72?×?10³. In this optimum nanocrystalline state, the material also exhibited a high Curie temperature above 1100?K, opening the scope of the present nanocrystalline alloy for high temperature applications.     

Fe73.5Cu1Nb3B9Si13.5非晶态合金的激波纳米晶化研究

实验表明,非晶态合金在激波影响下会转变为纳米晶.最近的实验进一步发现,Fe_73.5Cu₁Nb₃B₉Si_13.5非晶态合金中的Cu,Nb在激波晶化中的细化作用被抑制,且样品在这种转变之后作进一步的退火处理,其晶粒度变大而晶格常数变小.在激波晶化机理分析中提出了“激波流体晶化”构想. 关键词：