Spin-glass behavior and exchange bias in phase-separated Nd0.85Sr0.15CoO3

The magnetic properties of Nd_0.85Sr_0.15CoO₃ have been systematically investigated by dc magnetization, ac susceptibility and magnetic relaxation. The dynamics scaling analysis of ac susceptibility and magnetic relaxation give sufficient evidence of the existence of a spin-glass phase, which can be ascribed to the complicated interactions among Co³⁺ and Co⁴⁺ ions in this phase-separated compound. The field-cooled magnetic hysteresis loop displays both horizontal and vertical shifts, i.e., the exchange bias effect, while no shifts are present with increase of the measuring field up to ±50 kOe. The results further sustain the picture of the spin-glass phase coexisting with other magnetic regions in the sample.     

Effect of pressure sensitivity index on the deformation behavior of Zr41.2Ti13.8Cu12.5Ni10Be22.5 metallic glasses

The effect of pressure sensitivity index on the deformation behavior in Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 metallic glasses was studied using the indentation tests. The results showed that the intersecting slip lines occurred in the as-cast samples when the metallic glasses was deformed, and their shear band quantity, length, and density decreased with increasing the pressure sensitivity index in the annealed samples. The plastic deformation size of the as-cast sample is higher than that of the annealed samples under all the loads. It is therefore indicated that the pressure sensitivity index can affect strongly the deformation behavior and morphological characteristics of shear band of the metallic glasses.     

High-temperature phase transition and magnetic property of LaFe11.6Si1.4 compound

The LaFe_11.6Si_1.4 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K(5 h) to 1623 K(2 h). The powder X-ray diffraction and metallographic microscopy show that 1423 K and 1523 K are two curial temperatures, at which large amount of 1:13 phase begins to form and the most amount of 1:13 phase is obtained, respectively. With annealing temperature increasing to 1573 K and 1623 K, a new phase of La₅Si₃ is detected in LaFe_11.6Si_1.4 compound. According to the DSC curve of as-cast LaFe_11.6Si_1.4 compound and the X-ray patterns of annealed LaFe_11.6Si_1.4 compounds, the high-temperature phase transition process is analyzed. For studying the influence of different high-temperature and short-time annealing on the Curie temperature, thermal and magnetic hysteresis, magnetocaloric effect of LaFe_11.6Si_1.4 compound annealed at different temperatures are also investigated.     

Effect of hydrostatic pressure on the decomposition behavior of Cu54Zr22Ti18Ni6 bulk metallic glass alloy in supercooled liquid region

The effect that hydrostatic pressure has on the decomposition behavior in Cu₅₄Ni₆Zr₂₂Ti₁₈ bulk metallic glass (BMG) alloy was assessed using samples, which were isothermally annealed in the supercooled liquid region (SLR) with and without application of hydrostatic pressure. During subsequent annealing for the thermal analysis, the samples annealed under hydrostatic pressure displayed a slower crystallization process in the SLR, which is attributed to a retarded compositional decomposition of the BMG alloy under pressure.     

Influence of the TbFe2 crystallization on the magnetic and magnetostrictive properties of (Fe3Ga/TbFe2)n heterostructures

In this work we have investigated (Fe₃Ga/TbFe₂)_n multilayers grown by sputtering at room temperature. These multilayers exhibit a large coercivity associated to the crystalline TbFe₂ Laves phase. To reduce the coercivity it is necessary to control the crystallization of that material. In this work, we focus on the analysis of the properties of the TbFe₂ layers. In the as-grown heterostructures we have found evidence of nanoaggregates in the TbFe₂ layers. The Fe₃Ga thickness and the thermal treatments have an influence on the volume of these nanoprecipitates. In the annealed samples, when increasing the Fe₃Ga thickness we observe a decrease in the nanoaggregate volume and thus in the coercivity. The experimental results indicate that the crystallization of the TbFe₂ depends on the Tb diffusion promoted by the thermal treatment and on the stiffness factor (Y/α) of the Fe₃Ga layer. The magnetostrictive properties are also strongly influenced by the crystallization of the TbFe₂. We have achieved a maximum magnetostriction constant of nearly 550 ppm with a coercive field close to 400 Oe.     

Effects of annealing at high pressure on structure and mechanical properties of Al87Ni7Gd6 metallic glass

The effects of annealing and annealing with a superimposed pressure of 940 MPa on the primary crystallization behaviour of α-Al and the resulting micro-hardness have been studied for as-quenched Al₈₇Ni₇Gd₆ metallic glass. Isothermal annealing experiments were conducted for 30 min at 188 °C, 191 °C, and 205 °C in silicone oil maintained either at atmospheric pressure (i.e. 0.1 MPa) or at 940 MPa. XRD analyses detected the evolution of structure with annealing at 0.1 MPa, while specimens annealed with 940 MPa pressure exhibited sharper diffraction peaks than those annealed at 0.1 MPa. DSC measurements were conducted on the as-received amorphous ribbons as well as ribbons annealed at different temperatures at either 0.1. MPa or with 940 MPa superimposed pressure. Specimens annealed with 940 MPa pressure exhibited higher onset temperatures (i.e. T_x1) and temperatures for the first exothermic peak (i.e. T_p1) for primary crystallization. TEM measurements revealed an increase in the volume fraction of α-Al with increases in annealing temperature, while micro-hardness measurements revealed an increase in hardness with increasing amounts of α-Al. Specimens annealed with 940 MPa pressure exhibited further increases in both the volume fraction of α-Al and resulting micro-hardness.     

Influence of thermally induced structural transformations on hardness in Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy

Effect of heat treatment on mechanical behavior of Fe_89.8Ni_1.5Si_5.2B₃C_0.5 amorphous alloy was investigated by measuring microhardness. It was shown that the as-prepared amorphous alloy has an unexpectedly high microhardness. This can be attributed not only to boron dispersed in the alloy, but also to the structure which exhibits aspects of a nanocomposite of nanoparticles dispersed in an amorphous matrix. As the alloy crystallizes at temperatures above 540 °C, microhardness decreases continuously as a function of heating temperature. This is attributed to separation of boron out of the amorphous matrix into nanocrystals of Fe₂B phase. Further decrease in microhardness is attributed to crystallite growth with the accompanying change in the dominant nature of the interfaces from amorphous/crystal to crystal/crystal, and creation of a porous structure. When the crystallization is complete, the alloy exhibits microhardness close to that of a hypothetical mixture of α-Fe and Fe₂B phases of the same composition.     

Martensitic transformation of Ni64Al34Re2 shape memory alloy

As-rolled and annealed Ni₆₄Al₃₄Re₂ shape memory alloy (SMA) exhibits B2 → L1₀ (3R) martensitic transformation with M_s temperature up to about 210 °C. Experimental results indicate that the annealing temperature is the major factor that affects the M_s temperature. It is found that adding 2 at.% Re to replace Al in Ni₆₄Al₃₆ binary SMA can significantly refine the alloy's grain size and enhance the softening behavior during transformation. Meanwhile, Re has the same trend as Ni to affect the M_s temperature, but it has a less effect than Ni. The lattice constants and microstructures of NiAl-B2 phase, NiAl-L1₀ (3R) martensite and Ni₃Al-L1₂ phase are almost similar to those of Ni–Al binary SMAs.     

Structure and crystallization kinetics of a Cu50Zr45Ti5 glassy alloy

The crystallization kinetics and structure changes in a melt-spun Cu₅₀Zr₄₅Ti₅ glassy alloy on heating were investigated by X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry and differential isothermal calorimetry. The glassy phase in the Cu₅₀Zr₄₅Ti₅ alloy was crystallized forming Cu₁₀Zr₇ and CuZr₂ phases upon thermal annealing. The activation energy for crystallization obtained by the Arrhenius equation was 435 kJ/mol. The crystallization process took place by nucleation and growth mechanism, and an Avrami exponent of about 3.3 may indicate a three-dimensional interface-controlled growth of nuclei with a decreasing nucleation rate.     

The synthesis of nanocrystalline Ni75Nb12B13 alloys by high energy ball milling of elemental components

Ni₇₅Nb₁₂B₁₃ alloys were synthesized by mechanical alloying (MA) of individual Ni, Nb and B components. X-ray investigation showed the formation of Ni (Nb, B) solid solution and amorphous phase at the intermediate stage of milling. Metastable phases formed by MA turned into Ni (Nb), Ni₂₁Nb₂B₆ and Ni₃Nb stable phases during heating up to 720 °C. The exothermal effects on DSC curves were caused with these processes. The disintegration of Ni (Nb, B) solid solution and crystallization of an amorphous phase resulted in the stable phases formation during the milling prolongation as well as after thermal treatment.     

Fe72-xNd7B21Nbx(x=0~4.0)块体合金晶化过程和磁性能的研究

采用铜模吸铸法制备了直径为2mm的Fe_(72-x)Nd_7B_(21)Nb_x(x=0~4.0)块体合金,利用X射线衍射仪(XRD)、差示扫描量热仪(DSC)、振动样品磁强计(VSM)和多功能物理性质测量系统(PPMS)研究了Nb含量对该体系合金非晶形成能力、晶化行为及磁性能的影响。结果表明:适当的添加Nb有助于提高该体系合金的非晶形成能力,当Nb含量为2.0at%,2.2at%和2.5at%时,可以获得基本为非晶结构的块体合金。Nb含量对该体系合金的晶化行为有着重要影响,Nb含量为2.5at%的合金在晶化过程中能有效抑制非磁性相的析出,增强了晶粒间的交换耦合作用,使得其剩磁得到明显的提高,具有最佳的综合磁性能:B_r=0.63T,H_(ci)=448.97kA/m,(BH)_(max)=36.32kJ/m~3。     

The magnetic, structure and mechanical properties of rapidly solidified (Nd7Y2.5)-(Fe64.5Nb3)-B23 nanocomposite permanent magnet

The Nd₇Y_2.5Fe_64.5Nb₃B₂₃ nanocomposite permanent magnets in the form of rods with 2 mm in diameter have been developed by annealing the amorphous precursors produced by copper mold casting technique. The phase evolution, structure, magnetic and mechanical properties were investigated with X-ray diffractometry, differential scanning calorimetry, electron microscopy, magnetometry and universal uniaxial compression strength techniques. The heat treatment conditions under which the magnets attained maximum magnetic and mechanical properties have been established. The results indicate that magnet properties are sensitive to grain size and volume content of the magnetic phases present in the microstructure. The composite microstructure was mainly composed of soft α-Fe (20-30 nm) and hard Nd₂Fe₁₄B (45-65 nm) magnetic phase grains. The maximum coercivity of 959.18 kA/m was achieved with the magnets annealed at 760 °C whereas the highest remanence of 0.57 T was obtained with the magnets treated at 710 °C. The optimally annealed magnets possessed promising magnetic properties such as _jH_c of 891.52 kA/m, B_r of 0.57 T, M_r/M_s = 0.68, (BH)_max of 56.8 kJ/m³ as well as the micro-Vickers hardness (H_v) of 1138 ± 20 and compressive stress (σ_f) of 239 ± 10 MPa.     

Phase transformations in face centered cubic (Al0.32Cr0.68)2O3 thin films

Face centered cubic (Al_0.32Cr_0.68)₂O₃ thin films have been annealed in the temperature range of 500–1000 °C during 2–8 h. The fcc structure of the film remains intact when annealed at temperatures up to 700 °C for 8 h. X-ray diffraction and transmission electron microscopy show the onset of phase transformation to corundum phase alloys in the sample annealed at 900 °C for 2 h, where annealing at 1000 °C for 2 h results in complete phase transformation to α-(Al_0.32Cr_0.68)₂O₃. In-plane and out-of-plane line scans performed in EDX TEM and θ/2θ XRD patterns did not show any phase separation into α-Cr₂O₃ and Al₂O₃ prior and after the annealing. The apparent activation energy of this process is 380–480 kJ/mol as determined by the Johnson–Mehl–Avrami model.     

快淬参数对Nd9.5Fe84B6.5合金磁性能和微观结构的影响

本文采用直接快淬法制备了Nd_9.5Fe₈₄B_6.5合金,研究了腔室压力和甩带速度这两个快淬参数对其磁性能和微观结构的影响,建立了两者之间的关联性。研究发现：熔体快淬过程中在其它条件保持不变时,腔室压力和甩带速度之间存在着互相补偿的关系。腔室压力为0.03 MPa、快淬速度为19 m/s时制备的条带样品与腔室压力为0.05 MPa、快淬速度为15 m/s时制备的样品厚度和磁性能的数值相近。X 射线衍射和透射电子显微镜的结果表明：这两种条件下得到的条带样品具有相同的相组成和相似的微观结构。因此,通过调整腔室压力和甩带速度可以得到微观结构和磁性能相近的条带样品,这将为制备高性能的稀土永磁材料及其工业化生产提供指导。     

Microstructural characteristics of Nd2Fe14B/α-Fe nanocomposite ribbons bearing Nb element

The effects of Nb on the microstructure and magnetic properties of (Nd_0.9Dy_0.1)_9.5Fe_79-xCo₅Nb_xB_6.5 (x = 0, 1) nanocomposite magnets were investigated. A fine and uniform microstructure was achieved for the ribbons annealed at 710°C for 4 min, enhancing the interaction coupling between grains and improving the magnetic properties. The results of three-dimensional atom probe (3DAP) indicated that Fe-Nb-B intergranular phase existed at the grain boundaries, suppressing the grain growth during the crystallization process. The coercivity was improved from 224 to 643 kA/m for the modification of the microstructure.     

The effect of the substitution of Cu for Ni on magnetoresistance and magnetocaloric properties of Ni50Mn34In16

The effect of the substitution of Cu for Ni on the magnetoresistance behaviour and the magnetocaloric properties of the Ni₅₀Mn₃₄In₁₆ alloy has been investigated. The (Ni-Cu)₅₀Mn₃₄In₁₆ alloys crystallize in the cubic L2₁ structure in austenite phase. While the M_s temperature is about 160 K for the Ni_47.5Cu_2.6Mn_34.0In_15.9 alloy, the martensitic transition is not observed for Ni_45.5Cu_4.6Mn_33.8In_16.1 alloy. To estimate the magnetic entropy change of the Ni_47.5Cu_2.6Mn_34.0In_15.9 alloy, the magnetization measurements as function of magnetic field are performed by continuous and noncontinuous heating methods. The Ni_47.5Cu_2.6Mn_34.0In_15.9 alloy shows the magnetostructural transition whose irreversible ratio is about 50% at 160 K. The magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition. For the magnetic field change of 2 T, giant magnetoresistance value is about −68% that is rather big among the similar bulk alloys.     

Microwave-assisted synthesis and characterization of Nd1.5Mg17Ni0.5-Fe3O4 hydrogen storage composite

This work reports the preparation of Nd_1.5Mg₁₇Ni_0.5-Fe₃O₄ hydrogen storage composite in a single mode 2.45 GHz microwave cavity. The physicochemical properties (thermodynamic and kinetic characteristics, hydrogen absorption/desorption properties, thermal behavior, phase composition and morphology) were characterized by pressure-composition isotherms, differential scanning calorimetry, X-ray diffraction, scanning electron microscope with an energy dispersive X-ray spectrometer, transmission electron microscopy, and laser granulometry. The proposed microwave synthesis, in contrast with conventional sintering method, offers rapid heating, makes homogenous composition and hence improves the hydrogen storage properties of the composite.     

Room-temperature flow in a metallic glass - Strain-rate dependence of shear-band behavior

The rate dependence of serrated flow in amorphous Al_86.8Ni_3.7Y_9.5 has been investigated by nanoindentation. Three samples, containing different initial amounts and distributions of free volume, were used: as quenched, cold rolled and annealed below the crystallization temperature. When the cold-rolled sample is indented at low rates, no new shear bands form, and stable, time-dependent, flow takes place at pre-existing shear bands, well below the glass transition temperature. Aside from instrumental resolution, factors that likely affect serrated flow include the magnitude of the yield drop and the shear-band propagation velocity. The trends we observe are compared with calculations based on the free-volume theory.     

Magnetic and magnetocaloric properties in melt-spun and annealed Ni42.7Mn40.8Co5.2Sn11.3 ribbons

The Ni_42.7Mn_40.8Co_5.2Sn_11.3 ribbons were prepared by melt spinning. After heat treatment, the martensitic transformation temperature and Curie temperature of austenite of the annealed ribbons increased remarkably. Inverse and direct magnetocaloric properties were investigated in the melt-spun and annealed ribbons. The effective refrigerant capacities for these ribbons were discussed in this paper.     

Structure and thermal behavior of multicomponent Fe68−xNixZr15Nb5B12 (x = 5, 10, 15, 20) alloys

Multicomponent Fe_68−xNi_xZr₁₅Nb₅B₁₂ (x = 5, 10, 15, 20) alloy powders milled for 60 h were prepared by mechanical alloying (MA). The structure and crystallization behavior were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). Ni enhances the amorphisation of alloy powders. Particle size increases with increasing Ni content. Both onset crystallization temperature T_x and the first crystallization peak temperature T_p of the four alloys shift to a higher temperature with increasing heating rate while melting temperature (T_m) is just the opposite. Fe_68−xNi_xZr₁₅Nb₅B₁₂ (x = 5, 10, 15, 20) alloys all have a large supercooled liquid region ΔT_x. The supercooled liquid region ΔT_x increases and the crystallization activation energy E decreases with increasing Ni content.