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.     

Low temperature magnetic and magnetostrictive properties in Pr(Fe_(1-x)Co_x)_(1.9) cubic Laves alloys

The structures,spin reorientations,magnetic,and magnetostrictive properties of the polycrystalline Pr(Fe_(1-x)Co_x)_(1.9)(x=0–1.0)cubic laves phase alloys between 5 K and 300 K are investigated.Large low-field magnetostrictions are observed at 5 K in the alloys with x=0.2 and 0.4 due to the low magnetic anisotropies of these two alloys.A large negative magnetostriction of about-1130 ppm is found in PrCo_(1.9) alloy at 5 K.The magnetizations of the alloys with 0≤x≤0.6decrease abnormally at the spin reorientation temperature T_(sr),and an abnormity is detected in the alloy with x=1.0 at its Curie temperature T_c(45 K).The substitution of Fe by Co increases the value of T_(sr) in the alloy with x value increasing from 0.0 to 0.4,and then reduces the value of Tsr with x value further increasing to 0.6.     

Short range order transformation and magnetostriction of Fe83Ga17 ribbons

The relationship between magnetostriction and structure of melt-spun Fe 83 Ga 17 ribbons are investigated by XRD and M¨ossbauer spectrum technique(MS).As the heat-treatment temperature increases from 650℃ to 800℃,the magnetostriction coefficient of Fe 83 Ga 17 ribbon first increases and then decreases.The largest magnetostriction coefficient(578.4 ppm) is achieved in those specimens quenched at 750℃.According to the XRD and Mo¨ssbauer spectrum analysis,a small quantity of DO 3 phase is precipitated in Fe 83 Ga 17 ribbons when quenched from 650℃ and the DO 3 phase is gradually transformed into B2-like phase if quenched at higher temperature.However,both DO 3 and B2-like phases disappear when the temperature increases up to 800℃.From this point of view,B2-like phase might be beneficial to the enhancement of magnetostrictive properties of melt-spun ribbons.     

First-principle investigation on perovskite La_(1-x)Eu_xGaO_3

The pseudopotential method has been used to investigate the structural, electronic and magnetic properties of La_(1-x)Eu_xGaO_3(x = 0, 0.25, 0.5, 0.75, and 1) within the scheme of generalized gradient approximation. The spin-polarized calculations demonstrate that the ground state is an antiferromagnetic insulator for x ≤ 0.5, while it is ferromagnetic halfmetal at x 0.5. The substitutions of magnetic Eu ions for non-magnetic La ions produce and strength spin polarization,which forcefully urges the system from the insulator to the half metal. Meanwhile, Eu doping strengthens a stoner mechanism for ferromagnetism of La_(1-x)Eu_xGaO_3(x = 0.75 and 1), which may lead to a rapid increasing in the total magnetic moment and therefore, antiferromagnetic–ferromagnetic transition happens.     

Short range order transformation and magnetostriction of Fes3Ga17 ribbons

The relationship between magnetostriction and structure of melt-spun Fes3Ga17 ribbons are investigated by XRD and M5ssbauer spectrum technique （MS）. As the heat-treatment temperature increases from 650℃ to 800℃, the magnetostriction coefficient of Fes3Ga17 ribbon first increases and then decreases. The largest magnetostriction coeiffcient （-578.4 ppm） is achieved in those specimens quenched at 750oc. According to the XRD and MSssbauer spectrum anal- ysis, a small quantity of DO3 phase is precipitated in Fe83Ga17 ribbons when quenched from 650℃ and the DO3 phase is gradually transformed into B2-1ike phase if quenched at higher temperature. However, both DO3 and B2-1ike phases disappear when the temperature increases up to 800℃. From this point of view, B2-1ike phase might be beneficial to the enhancement of magnetostrictive properties of melt-spun ribbons.     

Magnetic properties and magnetostriction of PrxNd1-xFe1.9（0≤x≤1.0） alloys at low temperature

The crystal structure,magnetic and magnetostrictive properties of high-pressure synthesized Prx Nd1-xFe1.9(0≤x≤1.0) alloys were studied.The alloys exhibit single cubic Laves phase with MgCu 2-type structure.The initial magnetization curve reveals that Pr0.2Nd0.8Fe1.9 has a minimum magnetocrystalline anisotropy at 5 K.The magnetostriction curve at 5 K shows that Pr0.2Nd0.8Fe1.9 has a very good low-field magnetostrictive property,and the magnetostriction of the PrxNd1-xFe1.9 alloy in high magnetic field is attributable mainly to Pr.The temperature dependence of the magnetostriction(λ ||) at the field of 5 kOe shows that the substitution of Nd reduces the K 1 remarkably,and the values of λ|| of Pr0.2Nd0.8Fe1.9 and Pr0.8Nd0.2Fe1.9 alloys are nearly five times larger than that of the PrFe 1.9 alloy below 50 K;the λ|| of Pr0.8Nd0.2Fe1.9 reaches up to 1082 ppm at 100 K,which makes it a potential candidate for application in this temperature range.     

Structural, electronic, and magnetic properties of CrN under high pressure

The structural,electronic and magnetic properties of CrN under high pressure are investigated by first-principles calculations.The antiferromagnetic orthorhombic structure is identified to be the preferred ground state structure.It possesses a bulk modulus of 252.8 GPa and the nonzero magnetic moment of 2.33 μ B per Cr ion,which agree well with the experimental results.CrN undergoes structural and magnetic transitions from an antiferromagnetic rocksalt structure to a non-magnetic Pnma phase at 132 GPa.Under compression,the magnetic moment of the Cr ion reduces rapidly near the equilibrium and phase transition point,and the distribution of the density of states is broadened,but the form of overlap between the orbitals of Cr d and N p remains unchanged.The broadening of the band induces spin flipping,which consequently results in the smaller magnetic moment of the Cr ion.     

Physical properties and phase diagram of NaFe1-xVxAs

We grew a series of NaFe_1-xV_x As(0 ≤ x ≤ 0.03) single crystals and performed the measurements of resistance,magnetic susceptibility, and specific heat to study the superconducting phase diagram by doping V into Na Fe As. Both the structural and the spin-density-wave(SDW) transitions are slightly suppressed by V-doping. While superconducting transition temperature is enhanced to the maximum value of 15 K when the optimal doping level x = 0.007 and then is suppressed rapidly with further V-doping, displaying a small superconducting dome. Our results suggest that V-impurities should act as strong magnetic scattering centers which cause the sharp suppression of superconductivity in NaFe_1-xV_x As.     

Elastic Modulus of Fe72.5Ga27.5 Magnetostrictive Alloy

The elastic modulus of Fe72.5Ga27.5 magnetostrictive alloy is determined by testing ac impedance resonance frequency and first-principle calculations. The observed elastic modulus is 90.2 GPa for a directionally solidified sample and 103.4 GPa for a water-quenched sample tested in a dc magnetic field of 32. 7mT without compressive pre-stress. The bulk modulus by first-principles calculation is 179.3GPa which is basically consistent with the experimental result. The elastic modulus first increases and then decreases with increasing dc magnetic field, attributed to magnetostriction occurrence in the Fe72.5Ga27.5 alloy. The elastic modulus increases with increasing compressive pre-stress, resulting from the initial magnetic states change under the applied compressive pre-stress. The elastic modulus increases match well with the improved magnetostriction after quenching.     

Anomalous magnetostrictive effects in （La1—xTbx）2／3Sr1／3 MnO3

A series of (La_{1-x}Tb_x)_{2/3}Sr_{1/3}MnO_3 polycrystalline samples has been studied by means of x-ray diffraction, magnetostriction, and thermal expansion measurements. It has been found that this series undergoes a phase transition from a rhombohedral to an orthorhombic form at the doping level x≈0.20 at room temperature accompanied by an anisotropic magnetostriction up to －50×10^{-6} under a magnetic field of 1T. The linear and volume magnetostrictions vary with chemical composition, even change sign. At T=80K, the magnetostrictions for the samples of x=0.20 and 0.40 exhibit different behaviours. The sample of x=0.20 has positive volume and linear magnetostrictions and a negative anisotropic magnetostriction, while the sample of x=0.40 has an opposite behaviour. The magnitude of volume magnetostriction for both the samples is essential (～10^{-4}) at T=80K under a magnetic field of 4T. We conclude that these anomalous effects are due to the charge delocalization and the structural phase transition between orthorhombic and rhombohedral forms induced by the applied magnetic field.     

Strain-tuned magnetic properties in (Ga,Fe)Sb:First-principles study

In view of the importance of enhancing ferromagnetic(FM) coupling in dilute magnetic semiconductors(DMSs),the effects of strain on the electronic structures and magnetic properties of(Ga,Fe)Sb were examined by a first-principles study.The results of the investigation indicate that Fe_(Ga) substitution takes place in the low-spin state(LSS) with a total magnetic moment of 1μB in the strain range of-3% to 0.5%,which transitions to the high-spin state(HSS) with a total magnetic moment of 5μB as the strain changes from 0.6% to 3%.We attribute the changes in the amount and distribution of the total moment to the influence of the crystal field under different strains.The FM coupling is strongest under a strain of about0.5%,but gradually becomes weaker with increasing compressive and tensile strains.The magnetic coupling mechanism is discussed in detail.Our results highlight the important contribution of strain to magnetic moment and FM interaction intensity,and present an interesting avenue for the future design of high Curie temperature(T_C) materials in the(Ga,Fe)Sb system.     

Role of Ga-doping in iron-gallium alloy clusters

The structural and magnetic properties of Fe_n-m Ga_m （n=3 ～ 6,m=0 ～ 2;n=13,m=0 ～ 3） alloy clusters have been studied using density functional theory.The substitutional doping is favourable for small clusters with up to six atoms at low Ga concentration and substitutional Ga atoms in 13-atom clusters prefer surface sites.The Ga-doping generally could reduce the energetic stability but enhance the electronic stability of Fe clusters,along with a decrease of the local magnetic moments of Fe atoms around Ga dopants.These findings provide a microscopic insight into Fe-Ga alloys which are well-known magnetostriction materials.     

Different effects of Ce-doping on orbital and spin ordering in perovskite vanadate Sm_(1-χ)Ce_χ VO_3

The effects of Ce-doping on the phase transition of the orbital/spin ordering (OO/SO) are studied through the structural, magnetic, and electrical transport measurements of perovskite vanadate Sm1 x Ce x VO 3 . The measurements of structure show that the cell volume decreases as x≤ 0.05, and then increases as Ce-doping level increases further. The OO state exists but is suppressed progressively in the sample with x≤0.2 and disappears as x0.2. The temperature at which the C-type SO transition is present increases monotonically with Ce-doping level increasing. The temperature dependence of resistivity for each of the samples shows a semiconducting transport behavior and the transport can be well described by the thermal activation model. The activation energy first decreases as x ≤0.2, and then increases for further doping. The obtained results are discussed in terms of the mixed-valent state of the doped-Ce ions.     

Structural changes concurrent with ferromagnetic transition

Ferromagnetic transition has generally been considered to involve only an ordering of magnetic moment with no change in the host crystal structure or symmetry, as evidenced by a wealth of crystal structure data from conventional X-ray diffractometry (XRD). However, the existence of magnetostriction in all known ferromagnetic systems indicates that the magnetic moment is coupled to the crystal lattice; hence there is a possibility that magnetic ordering may cause a change in crystal structure. With the development of high-resolution synchrotron XRD, more and more magnetic transitions have been found to be accompanied by simultaneous structural changes. In this article, we review our recent progress in understand- ing the structural change at a ferromagnetic transition, including synchrotron XRD evidence of structural changes at the ferromagnetic transition, a phenomenological theory of crystal structure changes accompanying ferromagnetic transitions, new insight into magnetic morphotropic phase boundaries (MPB) and so on. Two intriguing implications of non-centric symmetry in the ferromagnetic phase and the first-order nature of ferromagnetic transition are also discussed here. In short, this review is intended to give a self-consistent and logical account of structural change occurring simultaneously with a ferromagnetic transition, which may provide new insight for developing highly magneto-responsive materials.     

Crystal structure and magnetic properties of disordered alloy ErGa_(3-x)Mn_x

ErGa_(3-x)Mn_x disordered alloy is successfully prepared by the vacuum arc melting technology, and the crystal structure and magnetic properties are investigated by using the x-ray diffraction and magnetic measurements. The Rietveld structural analysis indicates that the ErGa_(3-x)Mn_x crystallizes into a cubic structure with space group of Pm3m in Mn doping range of x = 0–0.1. However, the disordered alloy with structural formula of Er_(0.8)Ga_2~Ⅰ(Ga~Ⅱ, Mn)0.4 as the second phase is separated from cubic phase for the samples with x = 0.2 and 0.3, which is induced by substituting the(Ga~Ⅱ, Mn)–(Ga~Ⅱ, Mn) pair at 2e crystal position for the rare earth Er at 1 a site. The lattice parameters tend to increase with Mn content increasing due to the size effect at Ga(1.30°A) site by substituting Mn(1.40°A) for Ga. The paramagnetic characteristic is observed by doping Mn into ErGa_3 at room temperature. With Mn content increasing from x = 0 to 0.1, the magnetic susceptibility χtends to increase. This phenomenon can be due to the increase of effective potential induced by doping Mn into ErGa_3.However, the magnetic susceptibility χ continues to decrease with the increase of Mn content in a range of x 0.2, which is due to the phase separation from the cubic Er(Ga, Mn)_3 to the hexagonal Er_(0.8)Ga_2(Ga, Mn)_(0.4).     

Change in the magnetic ground state of LaFe11.4Al1.6 compound by the substitution of Mn for Fe

The structure and magnetic properties of La(Fe_{1-x}Mn_x)_{11.4}Al_{1.6} (0≤x≤0.25)compounds have been studied. The NaZn_{13}-type structure is preserved and the lattice parameter increases linearly with increasing the Mn concentration. The magnetic ground state changes from the antiferromagnetic to the spin-glass or the cluster-glass state by the substitution of Mn for Fe. Furthermore, a field-induced transition from cluster glass to ferromagnet is found for the samples with x=0.05 and 0.10.     

Substituting AI for Fe in Pr（AlxFe1-x）1.9 alloys： Effects on magnetic and magnetostrictive properties

The magnetostrictive effects of substituting A1 for Fe in Pr（AlxFe1-x）1.9 （x = 0.0, 0.02, 0.05, 0.10） alloys between 5 K and 300 K were investigated. The substitution decreases the Curie temperature and the value of λ111. Fortunately, the substitution slightly increases the magnetostriction in a low magnetic field, which imbues these materials with potential advantages for applications. Rotation of the easy magnetization direction （EMD） from [ 111 ] to [ 100] in the Pr（A10.02Fe0.98）1.9 alloy as temperature decreases was detected by step scanned XRD reflections.     

Effect of Gd doping on the magnetism and work function of Fe1-xGdx/Fe（001）

The magnetism and work function Ф of Fe1-xGdx/Fe （001） films have been investigated using first-principles methods based on the density functional theory. The calculated results reveal that Gd doping on the Fe （001） surface would greatly affect the geometrical structure of the system. The restruction of the surface atoms leads to the transition of magnetic coupling between Gd and Fe atoms from ferromagnetic （FM） for 0.5 ≤x ≤ 0.75 to antiferromagnetic （AFM） for x = 1.0. For Fe1-xGdx/Fe （001） （x = 0.25, 0.5, 0.75, 1.0）, the charge transfer from Gd to Fe leads to a positive dipole formed on the surface, which is responsible for the decrease of the work function. Moreover, it is found that the magnetic moments of Fe and Gd on the surface layer can be strongly influenced by Gd doping. The changes of the work function and magnetism for Fe1-xGdx/Fe （001） can be explained by the electron transfer, the magnetic coupling interaction between Gd and Fe atoms, and the complex surface restruction. Our work strongly suggests that the doping of the metal with a low work function is a promising way for modulating the work function of the magnetic metal gate.     

Magnetism induced by Mn atom doping in SnO monolayer

The structural, magnetic properties, and mechanism of magnetization of SnO monolayer doped with 3 d transition metal Mn atom were studied using first-principles calculations. The calculated results show that the substitution doping is easier to realize under the condition of oxygen enrichment. Numerical results reveal that the spin-splitting defect state of the Mn doped system is produced in the band gap and the magnetic moment of 5.0 μB is formed. The induced magnetic moment by Mnsubis mostly derived from the 3 d orbital of the doped Mn atom. The magnetic coupling between magnetic moments caused by two Mn atoms in SnO monolayer is a long-range ferromagnetic, which is due to the hole-mediated p–p and p–d interactions. The calculated results suggest that room-temperature ferromagnetism in a SnO monolayer can be induced after substitutional doping of a Mn atom.     

Magnetostriction and spin reorientation in ferromagnetic Laves phase Pr(Ga_xFe_(1-x))_(1.9) compounds

The magnetostriction, magnetization, and spin reorientation properties in Pr(Ga_xFe_(1-x))_(1.9) alloys have been investigated by high-precision x-ray diffraction(XRD) step scanning, magnetization, and Mo¨ssbauer spectra measurements. Ga substitution reduces the magnetostriction(λ_(||)) with magnetic field H ≥ 8 kOe(1 Oe = 1.33322×10~2 Pa), but it also increases the λ|| value when H ≤ 8 kOe at 5 K. Spin-reorientations(SR) are observed in all the alloys investigated, as determined by the step scanned XRD, Mo¨ssbauer spectra, and the abnormal temperature dependence of magnetization. An increase of the spin reorientation temperature(T_(SR)) due to Ga substitution is found in the phase diagram, which is different from the decrease one in many R(T_x Fe_(1-x))_(1.9)(T = Co, Al, Mn) alloys. The present work provides a method to control the easy magnetization direction(EMD) or T_(SR) for developing an anisotropic compensation system.