Structure and magnetostriction of RFex (1.6 ? x ? 2.0) and R(Fe1−yTiy)1.8 (y ? 0.2) alloys (RDy0.65Tb0.25Pr0.1)

Structure, Curie temperature and magnetostriction of RFe_x (1.6 ? x ? 2.0) and R(Fe_1−yTi_y)_1.8 (y ? 0.2) alloys (RDy_0.65Tb_0.25Pr_0.1) have been investigated using optical microscopy, X-ray diffraction, AC initial susceptibility and standard strain gauge techniques. The homogenized RFe_x alloys are found to be essentially single phase in the range of 1.8 ? x ? 1.85. The second phase is a rare-earth-rich phase when x ? 1.8, and (Dy, Tb, Pr)Fe₃ phase when x ? 1.85. X-ray diffraction indicates that the R(Fe_1−yTi_y)_1.8 alloys contain a small amount of Fe₂Ti phase when y ? 0.05, which increases with the increment of Ti content. The Curie temperature of R(Fe₁−_yTi_y)_1.8 alloys slightly enhances with increasing Ti concentration when y ? 0.05, then remains almost unchanged in the range of 0.05 ? y ? 0.20. The magnetostriction of RFe_x alloys is improved when x ? 1.80 and reduced by increasing Fe content when x ? 1.85. The magnetostriction of R(Fe_1−yTi_y)_1.8 alloys is lowered by increasing Ti content.     

Structure, spin reorientation and M?ssbauer effect studies of Tb0.3Dy0.7(Fe1?xAlx)1.95 alloys

The effect of Al substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature and 77 K was investigated systematically. It was found that the primary phase of Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 is the MgCu₂-type cubic Laves phase structure when x < 0.4 and the lattice constant a of Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 increases approximately and monotonically with the increase of x. The substitution of Al leads to the fact that the magnetostriction λ inceases slightly in a low magnetic field (H ⩽ 40 kA/m), but decreases sharply and is easily close to saturation in a high applied field as x increases, showing that a small amount of Al substitution is beneficial to a decrease in the magnetocrystalline anisotropy. It was also found that the spontaneous magnetostriction λ ₁₁₁ decreases greatly with x increasing. The analysis of the M?ssbauer spectra indicated that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry with the changes of composition and temperature, namely spin reorientation. A small amount of non-magnetic phase exists for x = 0.15 in Tb_0.3Dy_0.7(Fe_1−x Al_x)_1.95 alloys and the alloys become paramagnetic for x > 0.15 at room temperature, but at 77 K the alloys still remain magnetic phase even for x = 0.2. At room temperature and 77 K, the hyperfine field decreases and the isomer shifts increase with Al concentration increasing.     

Relation between structure and magnetism of TixFe100−x alloys within the C14 Laves-phase stability range

We report about X-ray and magnetic investigations on polycrystalline alloys with hexagonal C14 (MgZn₂) structure of the system Ti_xFe_100−x in the concentration range 30.5x36.5 around the Laves-phase composition TiFe₂ (Ti_33.3Fe_66.6). Neighboring compositions Fe₅₀Ti₅₀ (with B2 structure) and Ti₁₅Fe₈₅ and Ti₂₀Fe₈₀ (with BCC structure) have also been investigated. From the data we establish a magnetic phase diagram for the C14 range of the system, showing a rather sharp transition from mainly ferromagnetic ordering in the range x<32 to a mainly antiferromagnetic ordering in the range x>32. The results can be made plausible microscopically by taking the site dependence of the moments into account. A revised structural equilibrium phase diagram is also given.     

Structural and magnetic properties of Pr3(Fe1−xCox)27.5Ti1.5 (x=0.0, 0.1, 0.2, 0.3)

A novel class of Co-substituted 3 : 29 materials, Pr₃(Fe_1−xCo_x)_27.5Ti_1.5 (x=0, 0.1, 0.2, 0.3) have been synthesized. Rietveld analysis of X-ray powder diffraction patterns for the x=0, 0.1 and 0.2 compositions showed that nearly all of the compounds are formed in monoclinic symmetry, with A2/m space group with traces of α-Fe, whereas, in x=0.3, additional traces of a (Co/Fe)–Ti (1 : 12) phase are also seen. The saturation magnetization increases with Co concentration both at 5 and 300 K and is explained on the basis of a rigid band model. A magnetic transition is observed for x=0.1 near 240 K. A large increase in Curie temperature, of about 180 K for x=0.1 and about 110 K for the other concentrations, is discussed on the basis of the strengthening of TM–TM exchange by the preferential occupation of Co in some of the Fe sites originally participating in antiferromagnetic bonds.     

Magnetic properties and specific heat of LaMn1−xTixO3+δ (0<x0.2)

We present a magnetic study of the insulating perovskite LaMn_1−xTi_xO_3+δ (0<x0.2) including measurements of magnetization, susceptibility, and magnetic relaxation. The Curie temperature was found to decrease with increasing content of Ti. Two distinct magnetic transitions, irreversibility, non-exponential relaxation and aging effects confirm a reentrant spin–glass state for x=0.2. The time decay of the magnetization has an algebraic functional form for times up to 2 h. The specific heat also displays characteristic features of a spin–glass system by a linear low-temperature dependence and a broadened peak near the temperature of the reentrant transition.     

The effect of boron on the structure and magnetic properties of Pr0.15Tb0.3Dy0.55Fe1.85 alloy

The structure, Curie temperature and magnetostriction of Pr_0.15Tb_0.3Dy_0.55Fe_1.85−xB_x   (x=0–0.3$x=0–0.3$) alloys have been investigated using X-ray diffraction, AC susceptibility and standard strain gauge techniques. It was found that all the samples possess entirely MgCu₂-type cubic Laves structure. With increasing B concentration, the lattice parameter decreases, while the Curie temperature remains unchanged. The magnetostriction of Pr_0.15Tb_0.3Dy_0.55Fe_1.85−xB_x alloys at room temperature increases with increasing B concentration firstly, and then decreases slightly.     

Crystallization of amorphous Fe100−xPx (13x24) alloys

A study of the structure change with temperature in amorphous Fe₁₀₀−xP_x (13 x 24) alloys was carried out by measuring magnetization and thermal expansion and also by structural analysis using X-ray diffraction and differential thermal analysis (DTA). The structure of the amorphous alloys relaxes (the decrease of excess free volume) at temperatures 100–150 K below the crystallization temperatures. The alloys with x 15 transform into (α-Fe + amorphous) at about 600 K. The alloys with x15 transform into (α-Fe+amorphous+Fe₃P) at about 600 K. With further heating, the alloys transform into (α-Fe+Fe₃P) both of which are stable phases from the equilibrium phase diagram.     

Structural and optical properties of Ba(Ti1−x,Nix)O3 thin films prepared by sol–gel process

Ba(Ti_1−x,Ni_x)O₃ thin films were prepared on fused quartz substrates by a sol–gel process. X-ray diffraction and Raman scattering measurements showed that the films are of pseudo-cubic perovskite structure with random orientation and the change of lattice constant caused by Ni-doping with different concentrations is very small. Optical transmittance spectra indicated that Ni-doping has an obvious effect on the energy band structure. The energy gap of Ba(Ti_1−x,Ni_x)O₃ decreased linearly with the increase of Ni concentration. It indicates that the adjusting of band gap can be achieved by controlling the Ni-doping content accurately in Ba(Ti_1−x,Ni_x)O₃ thin films. This has potential application in devices based on ferroelectric thin films.     

Energy band gaps for the GaxIn1−xAsyP1−y alloys lattice matched to different substrates

A pseudopotential formalism within the virtual crystal approximation in which the effects of composition disorder are involved is applied to the Ga_xIn_1−xAs_yP_1−y quaternary alloys in conditions of lattice matching to GaAs, InP and ZnSe substrates so as to predict their energy band gaps. Very good agreement is obtained between the calculated values and the available experimental data for the alloy lattice matched to InP and GaAs. The alloy is found to be a direct-gap semiconductor for all y compositions whatever the lattice matching to the substrates of interest. The (Γ→Γ) band-gap ranges and the ionicity character are found to depend considerably on the particular lattice-matched substrates suggesting therefore that, for an appropriate choice of y and the substrate, Ga_xIn_1−xAs_yP_1−y could provide more diverse opportunities to obtain desired band gaps, which opens up the possibility of discovering new electronic devices with special features and properties.     

Crystallographic and magnetic properties of (Nd,Dy)3Fe27.5(Ti,Mo)1.5 compounds

A systematic study of the formation, structure and magnetic properties of (Nd,Dy)₃Fe_27.5(Ti,Mo)_1.5 compounds has been performed. Rietveld analyses of the X-ray patterns of the samples indicate that the concentrations of Ti and Mo affect the formation and structural properties slightly, whereas different rare-earth (Nd and Dy) contents influence them significantly. It is found that high Dy contents make it difficult to form the 3:29-type structures. The Curie temperatures of Nd_2.1Dy_0.9Fe_27.5Ti_1.5−xMo_x decrease monotonically as more Ti was replaced by Mo but their saturation magnetizations remain almost unchanged; in contrast, for Nd_3−yDy_yFe_27.5TiMo_0.5, their saturation magnetizations decrease monotonically with increasing Dy contents while their Curie temperatures are constant.     

Highly strained InxGa(1−x)As−InyAl(1−y)As (x>0.8,y<0.3) layers for short wavelength QWIP and QCL structures grown by MBE

Highly strained quantum cascade laser (QCL) and quantum well infrared photodetector (QWIPs) structures based on In_xGa_(1−x)As−In_yAl_(1−y)As (x>0.8,y<0.3) layers have been grown by molecular beam epitaxy. Conditions of exact stoichiometric growth were used at a temperature of 420°C to produce structures that are suitable for both emission and detection in the 2–5 μm mid-infrared regime. High structural integrity, as assessed by double crystal X-ray diffraction, room temperature photoluminescence and electrical characteristics were observed. Strong room temperature intersubband absorption in highly tensile strained and strain-compensated In_0.84Ga_0.16As/AlAs/In_0.52Al_0.48As double barrier quantum wells grown on InP substrates is demonstrated. Γ–Γ intersubband transitions have been observed across a wide range of the mid-infrared spectrum (2–7 μm) in three structures of differing In_0.84Ga_0.16As well width (30, 45, and 80 Å). We demonstrate short-wavelength IR, intersubband operation in both detection and emission for application in QC and QWIP structures. By pushing the InGaAs–InAlAs system to its ultimate limit, we have obtained the highest band offsets that are theoretically possible in this system both for the Γ–Γ bands and the Γ–X bands, thereby opening up the way for both high power and high efficiency coupled with short-wavelength operation at room temperature. The versatility of this material system and technique in covering a wide range of the infrared spectrum is thus demonstrated.     

A structural, magnetostrictive and M?ssbauer study of Tb0.3Dy0.7(Fe0.9 T 0.1)1.95 alloys

The effect of IIIA metal and transition metalT substitution for Fe on crystal structure, magnetostriction and spontaneous magnetostriction, anisotropy and spin reorientation of a series of polycrystalline Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 (T=Mn, Fe, Co, B, Al, Ga) alloys at room temperature were investigated systematically. It was found that the primary phase of the Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys is the MgCu₂-type cubic Laves phase structure for different substitution. The magnetostriction λ{ins} decrases greatly for the substitution of IIIA metal, B, Al and Ga, but is saturated more easily for Al and Ga substitution, showing that the Al and Ga substitution is beneficial to a decrease in the magnetocrystalline anisotropy of Tb_0.3 Dy_0.7 (Fe_0.9 T _0.1)_1.95 alloys. However, the substitution of transition metal Mn and Co decreases slightly the magnetostriction λ{ins}. It was also found that the effect of different substitutions on the spontaneous magnetostriction λ{in111} is distinct. The analysis of the M?ssbauer spectra indicates that the easy magnetization direction in the {110} plane deviates slightly from the main axis of symmetry for Al and Ga substitution, namely spin reorientation, but it does not change evidently for B, Mn and Co substitution.     

Superconductivity magnetism and low temperature specific heat in YBa2(Cu1−xFex)3O7−δ with δ0 and δ1

Magnetic and low temperature specific heat measurements have been performed on iron doped YBa₂(Cu_1−xFe_x)₃O_7−δ samples with different oxygen contents (δ0 and δ1). Iron doping induces an orthorhombic to tetragonal transition and a decrease of both T_c and diamagnetic signal. Low temperature specific heat measurements reveal a Schottky type anomaly for δ0 samples with x=0.01 (1.8 K) and x=0.02 (3 K). This anomaly is attributed to magnetic interactions within iron limited chains. A numerical analysis of this effect is proposed.     

Synthesis, phase and microstructure characteristics of Pb(Zr0.52Ti0.48)O3–(Bi3.25La0.75)Ti3O12 ceramics

Ceramics with formula (1 − x)Pb(Zr_0.52Ti_0.48)O₃–x(Bi_3.25La_0.75)Ti₃O₁₂ (when x = 0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1.0) were prepared by a solid-state mixed-oxide method and sintered at temperatures between 950 °C and 1250 °C. It was found that the optimum sintering temperature was 1150 °C at which all the samples had densities at least 95% of theoretical values. Phase analysis using X-ray diffraction indicated the existence of BLT- as well as PZT-based solid solutions with corresponding lattice distortion. Scanning electron micrographs of ceramic surfaces showed a plate-like structure in BLT-rich phase while the typical grain structure was observed for PZT-rich phase. The grain sizes of both pure BLT and PZT ceramics were found to decrease as the relative amount of the other phase increased. This study suggested that tailoring of properties of this PZT–BLT system was possible especially on the BLT-rich side due to its large solubility limit.     

Electronic structure studies of Mg0.95Mn0.05Fe2−2xTi2xO4 (0x0.8)

The electronic structure of Mg_0.95Mn_0.05Fe_2−2xTi_2xO₄ (0x0.8) compound is investigated using near edge X-ray absorption fine structure, (NEXAFS) spectroscopy measurements, carried out at O K, Fe and Ti L_3,2-edges at room temperature. The O K-edge spectra indicate that the Fe 3d orbitals have been considerably modified and a new spectral feature start dominating in the pre-edge region at higher Ti doping. The Fe 2p NEXAFS spectra exhibit a mixed valent Fe²⁺/Fe³⁺ states apart from the conversion of Fe³⁺ to Fe²⁺ with the substitution of Ti ions. The Ti L_3,2-edge spectra indicate that Ti ions remain unchanged at 4+ state. These variations in the host electronic structure due to Ti substitution are consistent with the dielectric and transport properties of the material.     

A method based on magnetic moment measurement to identify the structural transition of quenched Fe1 -xGax (x = 0.15ben 0.30) alloys

A method based on the measurement of Fe average atomic magnetic moment to identify the structural transition caused by the increase of Ga content in quenched Fe_{1 - x}Ga_x alloys (0.15 ≤ x ≤ 0.30) is proposed. The quenched Fe_{1 - x}Ga_x alloys show a change of the Fe average atomic magnetic moment from 2.25 μ_B to 1.78 μ_B and then to 1.58 μ_B, which corresponds to the structural transition from A2 to D0₃ and then to B2. The relationship between the structure and the magnetostriction is clarified, and the maximum magnetostriction appears in the A2 phase. The variation tendency of the magnetostriction is well characterized, which also reflects the structural transition.     

Weak ferromagnetism in BiFeO3 doped with titanium

The Bi_1−xA_xFe_1−xTi_xO₃ (A—Ca, Sr, Pb, Ba) and BiFe_1−xTi_xO_3+δ systems have been studied using X-ray, neutron powder diffraction and magnetization measurements in a magnetic field up to 14 T. It was found that all Bi_1−xA_xFe_1−xTi_xO₃ solid solutions are rhombohedral up to x=0.3. In the case of BiFe_1−xTi_xO_3+δ the rhombohedral distortion preserved up to x=0.11. A homogeneous weakly ferromagnetic state was found for Bi_1−xCa_xFe_1−xTi_xO₃ (0.15≤x≤0.25) and BiFe_1−xTi_xO_3+δ (0.06≤x≤0.11), probably due to magnetoelectric interactions, whereas Bi_1−xA_xFe_1−xTi_xO₃ (A—Sr, Pb, Ba) compounds above doping level x>0.1 seem to be collinear antiferromagnets.     

High magnetostriction at low fields of (Tb1−xDyx)0.2Pr0.8(Fe0.4Co0.6)1.88C0.05 intermetallic compounds

The structure and magnetostriction of the (Tb_1−xDy_x)_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 intermetallic compounds (0≤x≤1) were studied by X-ray diffraction and magnetic measurements. The formation of an approximate single Laves phase with a MgCu2-type cubic structure was observed in this series of compounds. It was found that the Curie temperature and the saturation magnetization of the compounds would decrease with increase in the Dy content up to x=1. The magnetostriction λ_a (λ_a=λ_‖-λ_⊥) gently rises when x≤0.6, and follows with a precipitous fall when x exceeds 0.6, with the highest value of λ_a being reached in the compounds with x=0.6. The magnetostriction of all the samples was observed to approach their own saturation in the magnetic fields higher than 4 kOe. This indicates that the addition of a small amount of Dy could effectively improve the low-field magnetostriction of the Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.88C_0.05 compounds, which could become a kind of promising magnetostrictive material.     

Structural and magnetic properties of hydrides R3Fe29−xVxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R₃Fe_29−xV_xH_y (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants , and c and the unit cell volume of R₃Fe_29−xV_xH_y decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce₃Fe_27.5V_1.5H_6.5, like Ce₃Fe_27.5V_1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R₃Fe_29−xV_x with R=Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce₃Fe_27.5V_1.5 and Gd₃Fe_28.4V_0.6 show the larger storage of hydrogen with y=6.5 and 6.9 in these hydrides.     

Reduction of hysteresis loss and large magnetocaloric effects in substituted compounds of itinerant-electron metamagnets La(FexSi1−x)13

The maximum value of hysteresis loss E_h^MAX due to the itinerant-electron metamagnetic (IEM) transition of La(Fe_xSi_1−x)₁₃ and the partially substituted compounds La_1−zCe_z(Fe_0.86Si_0.14)₁₃ and La_1−z′Pr_z′(Fe_0.86Si_0.14)₁₃ increases when the magnetocaloric effects (MCEs) become large. It should be noted that the reduction of E_h^MAX without the decrease of large MCEs is achieved in La_1−zCe_z(Fe_0.86Si_0.14)₁₃ and La_1−z′Pr_z′(Fe_0.86Si_0.14)₁₃. For both the compound systems mentioned above, the critical temperature T₀ for the IEM transition decreases and the difference between T₀ and the Curie temperature T_C becomes larger with decreasing T_C. These results are consistent with the magnetic phase diagram of La(Fe_0.86Si_0.14)₁₃ under hydrostatic pressure. Consequently, the reduction of E_h^MAX in La_1−zCe_z(Fe_0.86Si_0.14)₁₃ and La_1−z′Pr_z′(Fe_0.86Si_0.14)₁₃ is closely related with the magnetovolume effects.