Long period helimagnetism in the cubic B20 FexCo1−xSi and CoxMn1−x Si alloys

We report magnetization, resistivity and small angle neutron scattering experiments on cubic B20 Fe_xCo_1?x SI alloys (0.3 ? x ? 0.9) and Co_xMn_1?xSi allpys (x = 0.02, 0.04 and 0.06). The magnetically ordered Fe_xCo_1?xSi alloys and the Co_xMn_1?xSi alloys with x = 0.02 and 0.04 are found to be helimagnetic with very long period. The low temperature resistivity of the magnetically ordered Fe_xCo_1?xSi alloys exhibits an anomalous positive magnetic contribution. The occurence of the Dzyalosyinsky-Moriya spin-orbit type interaction in these non-centrosymmetric alloys is given as a possible explanation of the helimagnetic order.     

Electrochemical supercapacitor studies of hierarchical structured Co2+-substituted SnO2 nanoparticles by a hydrothermal method

Hierarchical structured Co-doped SnO₂ nanoparticles are prepared by a low temperature hydrothermal process. The structural and surface morphologies of the SnO₂ and Sn_1?xCo_xO₂ nanoparticles are studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The Sn_1?xCo_xO₂ nanoparticles form with a tetragonal rutile structure during the hydrothermal process without further calcination. The pseudocapacitance behavior of the Sn_1?xCo_xO₂ nanoparticles is characterized by cyclic voltammetry (CV) in 1.0 M H₂SO₄ electrolyte. The specific capacitance (SC) is found to increase with an increase in cobalt content. A maximum SC of 840 F g^?1 is obtained for a Sn_0.96Co_0.04O₂ composite at a 10 mV s^?1 scan rate.     

Structural and optical properties of amorphous GexSn1-x alloys

The structural and optical properties of amorphous Ge_xSn_1-x alloys have been studied in the range x ? 0.5. The atomic arrangement is found to be tetrahedral with a random nearest neighbor environment. Both the average and the minimum optical gaps decrease with increasing Sn content, with the latter extrapolating to 0 at x ≈ 0.0. It is suggested that the variation of the optical and electronic properties with Sn concentration will provide a sensitive test of current theories of amorphous solids.     

Mössbauer studies of the magnetic behavior of amorphous Mn x Sn1−x alloys

We present systematic low temperature in situ¹¹⁹Sn Mössbauer effect (ME) studies in vapor quenched amorphous Mn _x Sn_1?x (0.09<x<0.95) alloys between 150 and 4.2 K. It is shown that the magnetic behavior of the system is correctly displayed by the transferred magnetic hyperfine (hf) interactions detected at the¹¹⁹Sn site. Combining the results of the concentration dependence of the transferred magnetic hf field and the ordering temperature with recent ac-magnetic susceptibility data reported on this system, a complete magnetic phase diagram is proposed. The effect of an external magnetic field (up to about 3 T) on the spin correlations in the spin-glass state is also discussed.     

Effects of Co on the Néel temperature and thermal expansion in dilute CrFe alloys

The Néel temperature and thermal expansion characteristics of dilute CrFe alloys containing Co have been investigated. It has been found that the Néel temperature of Cr_99-xFe₁Co_x alloys (0.5?x?1) increases with increasing Co content and that these ternary alloys exhibit a large spontaneous volume magnetostriction, indicating Invar characteristics around room temperature. These behaviors are extremely different from those of CrFe and CrCo binary alloys.     

Theory of magnetic susceptibility of the narrow-gap semiconductors Pb(Sn)Te

The nonoscillating singular part of the susceptibility of Pb_1?xSn_xTe alloys is calculated. The dependence on the composition x, temperature and the carrier concetration is explained by the existence of the valence band, separated from the conduction band with a small energy gap.     

Hyperfine magnetic fields on Cd impurity in the Pd2MnIn1-xSnx and Pd2MnSn1-ySby heusler alloys

The TDPAC technique was used to measure the magnetic hyperfine field (mhf) acting on Cd impurity in the Heusler alloys Pd₂MnIn_1-xSn_x and Pd₂MnSn_1-ySb_y for various values of x and y in the range 0 ? x, y ? 1. The alloys of Pd₂MnIn_1-xSn_x are antiferromagnetic at the In-rich end and ferromagnetic at the Sn-rich end, with a transition region x ≈ 0.5?0.7 where both phases coexist; the alloys containing Sn/Sb are ferromagnetic for all values of y. The mhf on the Cd impurity in the antiferromagnetic, transition and ferromagnetic regions of Pd₂MnIn_1-xSn_x are respectively zero, -150 and -200 kOe. For the Sn/Sb alloys the field changes from -200 at the Sn-rich end to -235 kOe at the Sb-rich end. The values of the field very closely follow the trend of the ferromagnetic Curie temperatures for the same alloys as a function of the s-p electron concentration. The observed large distribution of field intensities (～20%) and the lower values of the field in the region x = 0.5?0.6 are attributed mainly to the effect of antiferromagnetic domains. The results are compared with previous Mössbauer mhf measurements at the sites of Sn and Sb in the same alloys as well as with measurements in other Heusler alloys.     

Structure,magnetic properties and magnetocaloric effects of Fe50Mn15−x Co x Ni35 alloys

Fe50Mn15-xCoxNi35(x=0,1,3,5,7)alloys were prepared by arc melting under purified argon atmosphere.The ingots were homogenized at 930°C for 90h followed by water quenching.The crystal structure,magnetic properties and magnetocaloric effects of the alloys were studied by X-ray diffraction(XRD)and MPMS-7-type SQUID.The results show that all samples still maintained a single-(Fe,Ni)-type phase structure.With the increase of the content of Co,the Curie temperatures of these alloys increased and exhibited a second-order magnetic transition from ferromagnetic(FM)to paramagnetic(PM)state near Curie temperature.The maximum magnetic entropy change and the relative cooling power of Fe50Mn10Co5Ni35alloy was 2.55 J/kg·K and 181 J/kg,respectively,for an external field change of 5T.Compared with rare earth metal Gd,Fe50Mn15-xCoxNi35 series of alloys have obvious advantage in resource price;their Curie temperatures can be tuned to near room temperature,maintain a relatively large magnetic entropy change at the same time and they are a type of potential magnetic refrigeration materials near room temperature.     

Crystallization and magnetic properties of melt-spun neodymium-iron alloys

The magnetic and crystallization properties of melt-spun Nd_1?xFe_x alloys are reported. By using high purity constituents and an extremely fine orifice (100–150 μm), amorphous alloys were prepared over the interval 0.4 ? x ? 0.8. Their magnetic properties, taken between 20–850 K in fields up to 95 kOe, are interpreted on the basis of a sperimagnetic structure; at high field the alloys from collinear ferromagnetic structures. Room temperature coercivities of the amorphous alloys are relatively low (1.5–2.0 kOe) but increase substantially at reduced temperatures; at 20 K, a maximum coercivity of 52 kOe was found for a Nd_0.4Fe_0.6 alloy. X-ray diffraction indicates that the melt-spun alloys crystallize by the precipitation of Nd metal and an unidentified Nd-Fe phase. Changes in magnetization and coercivity during crystallization are reported.     

Onset of magnetism in concentrated ternary alloys I

The onset of magnetism and the magnetic propreties of concentrated substitutional ternary alloys A(Fe_1?xB_x)₂ (A = Y, Zr, U; B = Mn, Co, Ni and Al), Y₂(Ni_1?xCo_x)₇, Y(Ni_1?xCo_x)₃, Y₆(Fe_1?xMn_x)₂₃ and Ti(Fe_1?xCo_x) as well as the amorphous alloy system (Fe_1?xNi_x)₇₇Si₁₀B₁₃ are discussed in terms of homogeneous and heterogeneous models based on the Stoner-, Edwards- Wohlfa arth- and the Landau theory of phase transitions of second order. For a detailed comparison of the nine ternary systems A(Fe, B)₂ (A = Y, Zr, U; B = Mn, Co, Al) we refer to a following paper. From the results obtained on alloying UNi₂ with Fe, Co and Cu we propose that the magnetic moment of UNi₂—contrary to UFe₂—resides mainly on U rather than on the Ni site. The appearance of magnetism in YNi_x compounds by either changing the Y : Ni ratio or substituting Ni by Co in YNi₃ and Y₂Ni₇ is mainly attributed to band effects for which a schematic N(E) curve is proposed. The breakdown of long-range magnetic order in Y₆(Fe, Mn)₂₃ seems to be caused by a lack of delocalized electrons and a preferential site occupation of Mn and Fe. The magnetic properties of Ti(Fe_1?xCo_x) change from an itinerant to a localized moment behaviour above and below x = 0.5 due to the occurrence of Fe antistructure atoms which drive the onset of long-range magnetic order. The occurrence of magnetism in amorphous alloys compared with that of crystalline alloys with a high degree of disorder may be characterized in a similar way.     

Magnetization and NMR study of amorphous Ni-P alloys in the paramagnetic concetration range

The temperature- and field-dependence of magnetization, and the ³¹P NMR linewidth and Knight shift of some amorphous Ni_100?xP_x alloys with 18? x ? 22 prepared by melt-quenching and electrodeposition were studied below room temperature. Although all the alloys investigated contain magnetic inhomogeneities, the amount and nature of which depend on impurities and on the details of sample preparation, it could be established that the amorphous matrix of Ni_100?xP_x alloys with x ? 18 exhibit Pauli paramagnetism and the Pauli susceptibility was found to decrease rapidly with P content. From the results, a similarity of the electronic structure and the short-range order in amorphous Ni-P alloys and in the crystalline Ni₃P compound is deduced.     

Effect of Fe addition on the crystallization behaviour and Curie temperature of CoCrSiB-based amorphous alloys

The crystallization behaviour and Curie temperature of melt-spun Co_{71? x} Fe _x Cr₇Si₈B₁₄ (x?=?0, 2, 3.2, 4, 6, 8 and 12?at.%) amorphous alloys have been studied. Differential scanning calorimetry (DSC) showed two stages of crystallization. The first stage of crystallization (T _X1) in the alloy with 6?at.%?Fe was the highest and it had the highest activation energy. X-ray diffraction studies revealed that the primary crystalline phase is hcp-(CoCr)₂Si for Fe-free alloy, whereas (CoFeCr)₂Si and (CoFeCr)₃Si phases were formed with the addition of Fe. hcp-Co was also formed along with these phases. The secondary crystalline phases were fcc-Co and various boron-rich phases. The Curie temperature of the alloys also changed with the addition of Fe to the system. Like the primary crystallization temperature, the Curie temperature of the alloys did not vary systematically with the Fe content. The addition of Fe to the Co-based system changes the nearest-neighbour interaction. This changes the exchange interaction between the transition metal elements. Due to the asymmetry in the Bethe–Slater curve, a systematic variation with Fe addition was not observed in the Curie temperature measurement.     

Studies on Co-Sn-Te thin films

Electrical and galvanomagnetic properties of Co _x Sn_1?x Te thin films have been studied. On the basis of small positive temperature coefficient of resistance, small and constant resistivity, low Hall coefficient and negligible magnetoresistance, it was concluded that CoTe-SnTe system is metallic. Discussion employing the Sondheimer’s model further corroborated the metallic nature of the thin films.     

Effect of annealing in an external magnetic field on the magnetic texture of Mo-containing nanocrystalline alloys

The magnetic texture of (Fe_1?x Co_x)₇₆Mo₈Cu₁B₁₅ (x = 0, 0.5) nanocrystalline alloys is studied for different amounts of nanocrystalline grains. The originally amorphous alloys were annealed in external longitudinal and transverse magnetic fields of 0.025 T and 0.8T, respectively. Mössbauer measurements were carried out at room and liquid nitrogen temperatures in order to gain information on the hyperfine interactions and the orientation of the magnetization. The obtained results are compared with those received from zero-field annealed samples. Magneto-optical Kerr effect (MOKE) was applied for the investigation of possible changes at the surface of the x = 0 ribbon as a function of annealing temperature and applied magnetic field. A combination of uniaxial anisotropy, which originates from the shape anisotropy, and four-fold anisotropy, which is a contribution from crystallites of nanometre size embedded in the residual amorphous matrix, is unveiled.     

Magnetic anisotropy,magnetostriction and intermediate range order in Co-P alloys

Coercivity, magnetostriction and saturation field as a measure of magnetic ansitropy energy have been investigated in Co_100-xP_x with 5 ? x ? 26. According to their magnetization curves and coercivities crystalline alloys (5 ? x ? 11) contain hcp-inclusions whereas amorphous material (12 ? x ? 26) is magnetically soft. The saturation magnetization is mainly determined by the nearest neighbour shell but magnetostriction is also correlated with the further environment of the cobalt atoms. The abrupt breakdown of the value |λ_s| of the saturation magnetostriction with increasing phosphorus content of the crystalline alloys points to a growing structural disorder. λ_s of the amorphous material depends on the saturation magnetization alone (λ_s ≈ σ₀²) which decreases with increasing phosphorus content. The small value of λ_s suggests that angular correlations do not exceed the second coordination shell.     

The influence of substitution of Co for Mn on magnetism of the HoMn6−xCoxSn6 compounds (0⩽x⩽0.25)

We have studied the effects of Co substitution for Mn on the structure and magnetic properties of the HoMn_6−xCo_xSn₆ compounds (0?x?0.25) with HfFe₆Ge₆-type structure (space group P6/mmm) by X-ray powder diffraction and magnetization measurements. A monotonic decrease of the lattice parameters a and c is observed with increasing Co content. While the compounds with x=0 and 0.05 exhibit ferrimagnetism in the whole temperature range, the compounds with 0.1?x?0.15 show ferrimagnetism, helimagnetism and re-entrant ferrimagnetism with decreasing temperature. For the compounds with x=0 and 0.05, the spin reorientation temperature is observed. A metamagnetic transition from helimagnetic magnetic ordering to ferrimagnetism is observed for the compounds with x=0.1 and 0.2. The results are summarized in the HoMn_6−xCo_xSn₆ magnetic phase diagram.     

Spin-disorder resistivity in the Cu2Mn(Al1−xSnx) heusler alloys

Electrical resistivity measurements have been performed on the Cu₂Mn(Al_1?xSn_x) Heusler alloys, where x = 0; 0.05; 0.10; 0.15, in the temperature range of 4–800 K. The experimental curves clearly show the importance of the ferromagnetic character on the resistivities of the alloys. The results obtained are in agreement with an interpretation in terms of a spin-disorder model.     

Mechanical properties of Co-Si-B amorphous alloys

The ternary amorphous systems Co_xSi₅B_95?x with 7070Si _y B_30?y with 5<y<18 were studied for their mechanical properties at room temperature. Structure sensitive parameters as density, Young's modulus, micro-hardness and crystallization temperature were investigated as a function of Co and Si contents. The value of density increases with higher Co content but not linearly as for Co-B. Young's modulus, micro-hardness and crystallization temperature decrease with increasing Co concentration. The packing fractionη was calculated using 12-coordinated Goldschmidt atomic radii. It is shown that changes in the proportions of metalloids contents in the alloys have more significant influence on the atomic structure and therefore on the mechanical properties than changes of Co content. The maximum tensile elastic strain for the Co-Si-B system was estimated. Influence of magnetic moment on Young's modulus is discussed.     

Magnetic properties and hydrostatic pressure effect on the curie temperature of (Co,Mn)2B amorphous alloys

The temperature dependence of magnetization and magnetic susceptibility and hydrostatic pressure effect on the Surie temperature (dT_c/dP) are measured for (Co_1-xMn_x)₂B (0?x?0.4) amorphous alloys and the results are compared with those of crystalline compounds with the same composition. The Curie temperature decreases linearly with an increasing Mn content but magnetization shows a maximum around x=0.15. The reciprocal magnetic susceptibility of all the prepared alloys obeys the Curie-Weiss law above T_c. The magnitude of the negative value of dT_c/dP decreases linearly with increasing x from about 1.1 K/kbar (x=0) to zero (x=0.4), the composition dependence of which is opposite to that of the crystalline compound. The composition dependence of the average magnetic moment per transition metal atom and the Curie temperature and dT_c/dP are analysed on the basis of the local environment and the pair order interaction mode, respectively.     

A mean-field study on the thermo-magnetic properties of GdxCo1−x amorphous alloys (0.16⩽x⩽0.25)

We present a mean-field study on the thermo-magnetic properties of Gd_xCo_1−x amorphous alloys in the 0.16⩽x⩽0.25 composition range. A single set of exchange integrals and fixed values of the angular momenta of Gd and Co fairly describe the temperature dependence of magnetization. The magnetic specific heat and magnetic entropy show field and composition dependence. Both the specific heat anomaly and the saturated entropy, at the temperature of the magnetic phase transition, increase with increasing Co concentration. The two magnetic subnetworks and their cross-interactions contribute differently to the specific heat.