Effect of annealing on superconductivity in Fe_(1+y)(Te_(1-x)S_x) system

We have synthesized polycrystalline samples of Fe1.11(Te1-xSx) and single crystals of Fe1+y(Te0.88S0.12),and characterized their properties.Our results show that the solid solution of S in the Fe1.11Te tetragonal lattice is limited,~10%.We observed superconductivity at ~8 K in both polycrystalline samples and single crystals.Magnetization measurements reveal that the volume fraction is small for this superconducting phase in both polycrystalline samples as-synthesized and single crystals as-grown.It is found that annealing in air enhances the superconducting fraction;the maximum fraction is almost 100% in the single crystals annealed in air at 300°C.We discuss the effect of annealing on superconductivity and transport properties at the normal state in the Fe1+y(Te1-xSx) system in terms of decrease of the excess Fe.     

SmCo_(1-x)Ir_xAsO体系的磁性和输运性质

采用固相反应法,制备出一系列SmCo1-xIrxAsO(x=0.05,0.1,0.15,0.2,0.25,0.3)多晶样品。XRD测试结果表明所有样品均具有ZrCuSiAs型四方结构,随着掺杂量的增加,晶格参数a变大,c变小。在x≥0.25时发现小部分杂相峰IrAs2,说明SmCo1-xIrxAsO体系单相样品较难制得。磁性测量结果表明,SmCo1-xIrxAsO在高温区表现出顺磁性。外场为10Oe时,掺杂量为0.05的样品随着温度的降低,依次在60K和45K附近出现铁磁转变和反铁磁转变,在低温区ZFC与FC曲线分离,出现明显的不可逆性。随着外磁场的增加,不可逆性受到抑制,铁磁转变温度TC向高温方向移动。增加掺杂量,样品铁磁反铁磁转变温度几乎不变,表明Ir掺杂对样品磁性没有影响。M-H曲线表明,温度T30K时,所有掺杂样品随着磁场的增加,均出现反铁磁(AFM)-铁磁(FM)的磁性转变,且转变磁场随温度的升高而减小。T=50K时,这种变磁性转变消失,样品表现出软铁磁特性。     

Magnetism and superconductivity in Eu(Fe_(1-x)Ni_x)As_2(x= 0,0.04)

We report Eu-local-spin magnetism and Ni-doping-induced superconductivity(SC)in a 112-type ferroarsenide system Eu(Fe_(1-x)Ni_x)As_2.The non-doped EuFeAs_2exhibits two primary magnetic transitions at ~100 and ~40 K,probably associated with a spin-density-wave(SDW)transition and an antiferromagnetic ordering in the Fe and Eu sublattices,respectively.Two additional successive transitions possibly related to Eu-spin modulations appear at 15.5 and 6.5 K.For the Ni-doped sample with x=0.04,the SDW transition disappears,and SC emerges at T_c=17.5 K.The Eu-spin ordering remains at around 40 K,followed by the possible reentrant magnetic modulations with enhanced spin canting.Consequently,SC coexists with a weak spontaneous magnetization below 6.2 K in Eu(Fe_(0.96)Ni_(0.04))As_2,which provides a complementary playground for the study of the interplay between SC and magnetism.     

The unique magnetic damping enhancement in epitaxial Co_2Fe_(1-x)Mn_xAl films

Uniform precession dynamics and its magnetic damping are investigated in epitaxial Co_2Fe_(1-x)Mn_xAl films by using the time-resolved magneto–optical Kerr effect under out-of-plane configuration.The decay time of uniform precession mode decreases, and thus the magnetic damping increases with the increase of external field.Moreover, the decay time decreases as x decreases, so that the enhancement of magnetic damping occurs in Fe-rich sample.Furthermore, the decay time decreases as the excitation fluence increases, which drops rapidly at low magnetic field comparing with the slow reduction at high magnetic field.This unique magnetic damping enhancement is attributed to the enhancement of homogeneous magnetization.     

Structural characterization of epitaxial Cr(x)Mo(1-x) alloy thin films

To develop a model system containing regularly spaced misfit dislocations for studies of the radiation resistance of nanoscale defects, epitaxial thin films of Cr, Mo, and Cr(x)Mo(1-x) alloys were deposited on MgO(001) by molecular beam epitaxy. Film compositions were chosen to vary the lattice mismatch with MgO. The film structure was investigated by x-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning transmission electron microscopy (STEM). Epitaxial films with reasonably high crystalline quality and abrupt interfaces were achieved at a relatively low deposition temperature, as confirmed by STEM. However, it was found by XRD and RBS in the channeling geometry that increasing the Mo content of the CrMo alloy films degraded the crystalline quality, despite the improved lattice match with MgO. XRD rocking curve data indicated that regions of different crystalline order may be present within the films with higher Mo content. This is tentatively ascribed to spinodal decomposition into Cr-rich and Mo-rich regions, as predicted by the Cr(x)Mo(1-x) phase diagram.     

Quenched Fe moment in the collapsed tetragonal phase of Ca_(1-x)Pr_x Fe_2As_2

We report 75As NMR studies on single crystals of rare-earth doped iron pnictide superconductor Ca1-xPrxFe2As2 . In both cases of x = 0.075, 0.15, a large increase of νq upon cooling is consistent with the tetragonal-collapsed tetragonal structure transition. A sharp drop of the Knight shift is also seen just below the structure transition, which suggests the quenching of Fe local magnetism, and therefore offers important understanding of the collapsed tetragonal phase. At even low temperatures, the 1/75T1 is enhanced and forms a peak at T ≈ 25 K, which may be caused by the magnetic ordering of the Pr3+ moments or spin dynamics of mobile domain walls.     

Negligible magnetism in excellent structural quality Cr(x)Ti(1-x)O(2) anatase: contrast with high-T(C) ferromagnetism in structurally defective Cr(x)Ti(1-x)O(2)

We reexamine the mechanism of ferromagnetism in doped TiO(2) anatase, using epitaxial Cr:TiO(2) with excellent structural quality as a model system. In contrast to highly oriented but defective Cr:TiO(2) (approximately 0.5 micro(b)/Cr), these structurally superior single crystal films exhibit negligible ferromagnetism. Similar results were obtained for Co:TiO(2). We show for the first time that charge-compensating oxygen vacancies alone, as predicted by F-center mediated exchange, are not sufficient to activate ferromagnetism. Instead, the onset of ferromagnetism correlates with the presence of structural defects.     

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.     

Magnetic properties and magnetoresistance of Co_xC_(1-x) granular films prepared by magnetron sputtering

Amorphous CoxC1-x granular films were prepared on n-Si(100) substrate by dc magnetron sputtering.The effects of Co concentration,film thickness and annealing temperature on the magnetic properties and magnetoresistance(MR) were investigated.After annealing at 500°C for 0.5 hour,the Co(002) peak of the CoxC1-x(x>2.5 at.%) films was observed,but cracks appeared in the films.Saturation magnetization Ms increased steadily with the increase of Co concentration from 2.5 at.% to 50 at.% and also increased with ann...     

Room-temperature ferromagnetism in a II-VI diluted magnetic semiconductor Zn(1-x)Cr(x)Te

The magnetic and magneto-optical properties of a Cr-doped II-VI semiconductor ZnTe were investigated. Magnetic circular dichroism measurements showed a strong interaction between the sp carriers and localized d spins, indicating that Zn(1-x)Cr(x)Te is a diluted magnetic semiconductor. The Curie temperature of the film with x=0.20 was estimated to be 300+/-10 K, which is the highest value ever reported for a diluted magnetic semiconductor in which sp-d interactions were confirmed. In spite of its high Curie temperature, Zn(1-x)Cr(x)Te film shows semiconducting electrical transport properties.     

Magnetic phase transitions induced by strong magnetic fields in Zn1-x Ga0.667x Cr2se4

Powders of the spinels Zn_1-x Ga_0.667x Cr₂Se₄ for x = 0.0, 0.1, 0.2, 0.3, 0.5 have been obtained. For these spinels magnetization measurements were carried out by induction in strong pulsed magnetic fields up to 20T, in the temperature range 2.9 K to 30 K.

For x = 0.0 (ZnCr₂Se₄) three phase transitions were observed, whilst for concentrations with x = 0.1, 0.2 and 0.3 there were only two and for x = 0.5 only one. A hypothesis on the magnetic structure of the various phases separated by these transition is put forward.     

Magnetic properties and magnetocaloric effects in Er_(1-x)Gd_xCoAl intermetallic compounds

The magnetism and magnetocaloric effect in Er1-xGdxCoAl(x = 0, 0.1, 0.2, 0.4, 0.6, 0.8, 1) were investigated. The Er1-xGdxCoAl compounds were synthesized by arc melting. With the increasing Gd content, the N′eel temperature(T N)linearly increases from 14 K to 102 K, while the magnetic entropy change(-?S M) tends to decrease nonmonotonously.Under the field change from 0 T to 5 T, the-?S M of the compounds with x = 0.2–1 are stable around 10 J/kg·K, then a cooling platform between 20 K and 100 K can be formed by combining these compounds. For x = 0.6, 0.8, 1.0, the compounds undergo two successive magnetic transitions, one antiferromagnetism to ferromagnetism and the other ferromagnetism to paramagnetism, with increasing temperature. The two continuous magnetic transitions in this series are advantageous to broaden the temperature span of half-peak width(δT) in the-?S M–T curve and improve the refrigeration capacity.     

Magnetic phase transition and magnetocaloric effect in Mn_(1-x)Zn_xCoGe alloys

The magnetic phase transition and magnetocaloric effect are studied in a series of Mn1-xZnxCoGe(x = 0.01, 0.02,0.04, and 0.08) alloys. By introducing a small quantity of Zn element, the structural transformation temperature of the MnCoGe alloy is greatly reduced and a first-order magnetostructural transition is observed. Further increasing the Zn concentration results in a second-order ferromagnetic transition. Large room-temperature magnetocaloric effects with small magnetic hysteresis are obtained in alloys with x = 0.01 and 0.02, which suggests their potential application in magnetic refrigeration.     

Negative Thermal Expansion of the Dy_2Fe_(16)Cr Compound

Structural, thermal expansion, and magnetic properties of the Dy_2Fe_(16)Cr compound are investigated by means of x-ray diffraction and magnetization measurements. The Dy_2Fe_(16)Cr compound has a hexagonal Th_2Ni_(17)-type structure. There exists a negative thermal expansion resulting from a strong spontaneous magnetostriction in the magnetic state of the Dy_2Fe_(16)Cr compound. The average thermal expansion coefficient is-0.794 × 10~(-5)/K in the temperature range 292–407 K. The spontaneous magnetostrictive deformation and the Curie temperature are discussed.     

Magnetic properties of multiferroics-semiconductors Eu(1-x)Ce(x)Mn2O5

Studies of magnetization, magnetoresistance, and magnetic oscillations in semiconductor-multiferroics Eu(1-x)Ce(x)Mn2O5 (x = 0.2-0.25) (ECMO) at temperatures ranging from 5 to 350 K in magnetic fields up to 6 T are presented. It is shown that phase separation and charge carrier self-organization in the crystals give rise to a layered superstructure perpendicular to the c axis. An effect of magnetic field cycling on the superstructure, magnetization, and magnetoresistance is demonstrated. X-ray diffraction studies of ECMO demonstrating the effect of magnetic field on the superstructure are presented. The de Haas-van Alphen magnetization oscillations in high magnetic fields and the temperature-induced magnetic oscillations in a fixed magnetic field are observed at low temperatures. Below 10 K the quantum corrections to magnetization due to the weak charge carrier localization in 2D superlattice layers occur. It is shown that at all the temperatures the Eu(1-x)Ce(x)Mn2O5 magnetic state is dictated by superparamagnetism of isolated ferromagnetic domains.     

双钙态矿Sr_2Fe_(1-x)Mn_xMoO_6体系的磁性和磁输运性质的研究(英文)

我们用X射线光电子能谱、以及相关的电性和磁性测量研究了Sr2Fe1-xMnxMoO6(0相似文献   

Magnetic properties of the Cr(0 0 1) surface studied by spin-polarized scanning tunneling spectroscopy

The magnetic properties of the Cr(0 0 1) surface have been studied by spin-polarized scanning tunneling spectroscopy (SP-STS). Spatially resolved mapping of the spectroscopic dI/dU signal at an energy close to the spin-polarized Cr(0 0 1) surface state allows the confirmation of the topological antiferromagnetic order of the Cr(0 0 1) surface. It is shown that the presence of screw dislocations leads to the formation of domain walls which exhibit a width of 120–170 nm. A long-period modulation of the SP-STS signal was not observed indicating that the bulk spin-density wave is modified at the surface due to symmetry breaking.     

Magnetic properties and magnetocaloric effects in(Ho_(1-x)Y_x)_5Pd_2 compounds

The crystal structure, magnetic and magnetocaloric properties of(Ho_(1-x) Y_(0.5))_5 Pd_2 compounds are investigated. All the compounds crystallize in a cubic Dy_5 Pd_2-type structure with the space group Fd3 m and undergo a second order transition from spin glass(SG) state to paramagnetic(PM) state. The spin glass transition temperatures T_g decrease from 26 K for x = 0 to 13 K for x = 0.5. In the PM region, the reciprocal susceptibilities for all the compounds obey the Curie–Weiss law. The paramagnetic Curie temperatures(θp) for Ho_5 Pd_2,(Ho_(0.75) Y_(0.25)_5 Pd_2, and(Ho_(0.5) Y_(0.5))_5 Pd_2 are determined to be 32 K, 30 K, and 22 K, respectively, and the corresponding effective magnetic moments(μeff) are10.8 μB/Ho, 10.3 μB/RE, and 7.5 μB/RE, respectively. Magnetocaloric effect(MCE) is anticipated according to the Maxwell relation, based on the isothermal magnetization curves. For a magnetic field change of 0–5 T, the maximum values of the isothermal magnetic entropy change-?SMof the(Ho_(1-x)Y_x)_5 Pd_2(x = 0, 0.25, and 0.5) compounds are determined to be 11.5 J·kg~(-1)·K~(-1), 11.1 J·kg~(-1)·K~(-1), and 8.9 K J·kg~(-1)·K~(-1), with corresponding refrigerant capacity values of 382.3 J·kg~(-1), 336.2 J·kg~(-1), and 242.5 J·kg~(-1), respectively.     

Evolution of magnetic properties in the normal spinel solid solution Mg(1-x)Cu(x)Cr2O4

We examine the evolution of magnetic properties in the normal spinel oxides Mg(1-x)Cu(x)Cr2O4 using magnetization and heat capacity measurements. The end-member compounds of the solid solution series have been studied in some detail because of their very interesting magnetic behavior. MgCr2O4 is a highly frustrated system that undergoes a first-order structural transition at its antiferromagnetic ordering temperature. CuCr2O4 is tetragonal at room temperature as a result of Jahn-Teller active tetrahedral Cu2+ and undergoes a magnetic transition at 135 K. Substitution of magnetic cations for diamagnetic Mg2+ on the tetrahedral A site in the compositional series Mg(1-x)Cu(x)Cr2O4 dramatically affects magnetic behavior. In the composition range 0 ≤ x ≤ ≈0.3, the compounds are antiferromagnetic. A sharp peak observed at 12.5 K in the heat capacity of MgCr2O4 corresponding to a magnetically driven first-order structural transition is suppressed even for small x. Uncompensated magnetism--with open magnetization loops--develops for samples in the x range ≈0.43 ≤ x ≤ 1. Multiple magnetic ordering temperatures and large coercive fields emerge in the intermediate composition range 0.43 ≤ x ≤ 0.47. The Néel temperature increases with increasing x across the series while the value of the Curie-Weiss Θ(CW) decreases. A magnetic temperature-composition phase diagram of the solid solution series is presented.     

Controlling the magnetic ground state in Cr1-x Vx films

We demonstrate the ability to control the magnetic phase diagram of Cr1-x Vx(110) thin films grown on a W(110) substrate. Using angle-resolved photoemission, we have mapped paramagnetic and commensurate and incommensurate antiferromagnetic phases as a function of temperature, film thickness, and composition. We show that surface-localized electron states play a key role in the observed phase behaviors and suggest from this that it might be possible to control the magnetic phase by applying an external electric field.