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.     

Magnetic properties of metallic glasses of the type Fe80−x Pd x B20 and Fe80−x Pt x B20

Amorphous alloys of the type Fe_80???xPd_xB₂₀ and type Fe_80???xPt_xB₂₀ for 0?≤?x?≤?50 have been investigated by means of ⁵⁷Fe Mössbauer spectroscopy and magnetisation measurements in temperatures from 4.2 up to 300 K. Curie temperatures and crystallisation temperatures are found by DTMG-DTA method. Mössbauer spectroscopy magnetic field is observed to visible increase for x?=?1 and 1.5% at room temperature for Pd, while a decrease is observed for higher x values. Curie temperature for Pd alloys has a maximum at x?=?4 with T _C?=?753 K, which supports enforcing influence of Pd at low concentrations of Pd for magnetic interactions. We discuss different explanations for these measurements and compare with other findings for high Pd concentrations and alloys with Pt instead of Pd.     

Ferrimagnetism in CsMn1−xNixF3 and CsMn1−xCoxF3

CsMn_1?xNi_xF₃ with 0.3≦x≦0.5 and CsMn_1?xCo_xF₃ with 0.4≦x≦0.65 have been found to be ferrimag with a Curie temperature 50±1K. The magnetic moment at 4.2 K is 1.42μ_B per formula-unit for CsMn_0.65Ni_0.35F₃, and 1.77μ_B for CsMn_0.6Co_0.4F₃. The crystal structure has been determined to be rhombohedral; it probably has a stacking of twelve CsF₃-layers in the unit cell in hexagonal representation. Magnetic properties have been explained on the assumption that a Ni(Co) ion has a strong preference for occupying one of three inequivalent sites in the structure. It has been suggested that the magnetic moments of one-quarter of the magnetic ions couple antiparallel to those of the other three-quarters so that ferrimagnetism appears. The Curie temperature has been discussed in the molecular field approximation.     

Magnetic and magnetocaloric properties of Gd1−xScxNi2 solid solutions

Magnetic and heat capacity measurements have been carried out on the polycrystalline Gd_1−xSc_xNi₂ solid solutions (0≤x≤1), which crystallize in the cubic C15 Laves phases superstructure (space group F4?3m). These solid solutions are ferromagnetic with a Curie temperature below 76 K. Their Curie temperature decreases from 75.4 K for GdNi₂ to 13.6 K for Gd_0.2Sc_0.8Ni₂. At high temperatures, all solid solutions, except ScNi₂, are Curie-Weiss paramagnets. The Debye temperature as well as phonon, conduction electron and magnetic contributions to the heat capacity have been determined from heat capacity measurements. The magnetocaloric effect has been estimated both in terms of isothermal magnetic entropy change and adiabatic temperature change for selected solid solutions in magnetic fields up to 3 T.     

Magnetic and Mössbauer studies of Ni substituted Li-Zn ferrite

Li-Zn ferrites substituted with Ni having the compositional formula Li_0.4−0.5xZn_0.2Ni_xFe_2.4−0.5xO₄ where x=0.02?x?0.1 in steps of 0.02 were fabricated by the citrate precursor method. This method has been employed to get nanosized particles and good magnetic properties. The spinel phase structure of the prepared ferrites was confirmed by XRD analysis. The effect of Ni concentration on magnetic properties such as saturation magnetization and Curie temperature were investigated. A good knowledge of these magnetic properties is desirable from application point of view. The values observed are large and both quantities were found to decrease with substitution. The saturation magnetizations were found to vary from 78 to 94 emu/gm while the Curie temperature which limits the operating temperature of the system ranges between 563 and 584 °C. Mössbauer data were also recorded at room temperature and the hyperfine parameters like isomer shift, quadrupole splitting and internal magnetic field estimated. The results obtained and mechanisms involved are discussed.     

Magnetic ordering in Mg−Zn ferrites

The magnetic ordering of a series of magnesium-zinc ferrite, Zn_0.3Mg _x Fe_2.7?x O_4±δ (0.5≤x≤1.1; 0≤δ≤0.2) has been investigated using Mössbauer measurements in the temperature range 295–620 K. The samples were found to be magnetic at room temperature with a hyperfine field at each site which increases with iron content. The Curie temperature was also observed to increase in a similar manner. The slope of this increase forB _hf andT _c is steeper forx≤0.6 thanx≥0.7. It has also been observed that Mg²⁺ substitution by Zn²⁺ in MgFe₂O₄ affects the magnetic ordering and the internal hyperfine field. The Curie temperature decreases by ～200 K andB _hf by ～20%.     

Structure and magnetism of the Pr2Fe14-xCoxB system

Isostructural, tetragonal materials were synthesized for the entire composition range (x = 0 to 14). They were studied by X-ray and magnetometry methods. Magnetization measurements confirm a ferromagnetic arrangement of 3d and Pr magnetic moments and reveal a sharp increase of the Curie temperature with the increase of Co concentration. Saturation magnetization at 295 and 77 K reaches a slight maximum around x = 1 and gradually decreases for higher Co content. Anisotropy fields initially decrease and afterwards increase very quickly as more Co is introduced to the system. A spin reorientation occurs in alloys with x ⩾ 9.5 at temperature higher than 660 K. It marks a transition between uniaxial anisotropy and planar anisotropy. Spin reorientation temperature becomes lower for materials with higher Co content. A discussion of the Curie temperature change is conducted in terms of preferential substitution of Co into 16k₂ sites. The weakening of the exchange interaction between Pr and 3d sublattices, as well as the decreasing Pr-sublattice anisotropy with rising temperature, are considered to be responsible for anisotropy field changes. The interplay between crystal field and exchange field interactions is emphasized. A comparison with the Nd₂Fe_14-xCo_xB system is included.     

The influence of Al substitution on the phase transitions and magnetocaloric effect in Ni43Mn46Sn11−xAlx alloys

The effects of Al substitution on the phase transitions and magnetocaloric effect of Ni₄₃Mn₄₆Sn_11−xAl_x (x=0-2) ferromagnetic shape memory alloys were investigated by X-ray diffraction and magnetization measurements. With the increase of Al content, the cell volume decreases due to the smaller radius of Al, and the martensitic transformation temperature increases rapidly, while the Curie temperature of austenitic phase shows a small increase. A large positive and a negative magnetic entropy change were observed near the first-order martensitic transition and the second-order magnetic transition, respectively. The magnetic entropy changes, hysteresis behavior, and refrigerant capacity near the two transitions are compared.     

Curie temperatures and crystallization behavior of amorphous Fe81−xNixZr7B12 (x=10, 20, 30, 40, 50, 60) alloys

Curie temperature, crystal structure and crystallization behavior of amorphous alloys with the stoichiometry Fe_81−xNi_xZr₇B₁₂ (x=10–60) have been studied by X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and AC-magnetization (TMAG) measurements as functions of temperature. The thermal stability of long-range magnetic order, T_C vs. Ni content in as-quenched amorphous alloys exhibits maximum at 352 °C for x=40. The primary crystallization has been detected during annealing at the first crystallization stage of all ribbons investigated.     

Magnetic properties and phase diagram of ZnxNi1−xFe2O4: High-temperature series expansions

Using mean field theory and high-temperature series expansions (HTSEs), extrapolated with the Padé approximants method, the effect of Zn doping on magnetic properties of NiFe₂O₄ ferrite spinel has been studied. The nearest neighbour super-exchange interactions for intra-site (J_AA, J_BB) and inter-site (J_AB) of the Zn_xNi_1−xFe₂O₄ ferrites spinels, in the range 0≤x≤1, have been computed using the probability approach, based on Mössbauer data. The paramagnetic Curie-Weiss temperature θ and the Curie temperature T_C are calculated as a function of Zn concentration. The critical exponent γ associated with magnetic susceptibility is calculated. The spin correlation functions intra-plane and inter-plane have been also computed and compared with exchange couplings. The obtained theoretical results are in good agreement with experimental ones obtained by magnetic measurements and Mössbauer spectroscopy.     

Magnetic properties and specific heat of Dy1−xLaxNi2 compounds

Magnetic and specific heat measurements have been carried out on polycrystalline series of single-phase Dy_1−xLa_xNi₂ (0?x?1) solid solutions. The compounds have a Laves-phase superstructure (space group F4¯3m) with the lattice parameter gradually increasing with decreasing Dy content. The samples with x?0.8 are ferromagnetic with the Curie temperature below 22 K. At high temperatures, all solid solutions are Curie-Weiss paramagnets. The Debye temperature, phonon and conduction electron contributions as well as a magnetic contribution to the heat capacity have been determined from specific heat measurements. The magnetocaloric effect was estimated from specific heat measurements performed in a magnetic field of 0.42 and 4.2 T.     

Doping effect of Mn on the magnetic behavior in Ni-Zn ferrite nanoparticles prepared by sol-gel auto-combustion

The ferrite samples of a chemical formula Ni_0.5−xMn_xZn_0.5Fe₂O₄ (where x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized by sol-gel auto-combustion method. The synthesized samples were annealed at 600 °C for 4 h. An analysis of X-ray diffraction patterns reveals the formation of single phase cubic spinel structure. The lattice parameter increases linearly with increase in Mn content x. An initial increase followed by a subsequent decrease in saturation magnetization with increase in Mn content is observed showing inverse trend of coercivity (H_c). Curie temperature decreases with increase in Mn content x. The initial permeability is observed to increase with increase in Mn content up to x=0.3 followed by a decrease, the maximum value being 362. Possible explanation for the observed structural, magnetic, and changes of permeability behavior with various Mn content are discussed.     

Room-temperature ferromagnetism in Dy films doped with Ni

Temperature, magnetic field and spectral dependences of magneto-optical effects (MOEs) in bi-layer films Dy_(1−x)Ni_x-Ni and Dy_(1−x)(NiFe)_x-NiFe were investigated, x changes from 0 to 0.06. Peculiar behavior of the MOEs was revealed at temperatures essentially exceeding the Curie temperature of bulk Dy which is explained by the magnetic ordering of the Dy layer containing Ni under the action of two factors: Ni impurities distributed homogeneously over the whole Dy layer and atomic contact of this layer with continues Ni layer. The mechanism of the magnetic ordering is suggested to be associated with the change of the density of states of the alloy Dy_(1−x)Ni_x owing to hybridization with narrow peaks near the Fermi level character for Ni.     

The analysis of the magnetic properties in the intermetallic YxGd1−xNi3 compounds

In the paper an influence of Gd/Y substitution on the magnetic properties and exchange interactions of the Y_xGd_1−xNi₃ (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) polycrystalline compounds have been studied. The partial replacement of Gd by Y atoms is reflected in decreasing of the Curie temperature (T_C) as well as decreasing of effective the magnetic moment (μ_eff). It has been shown that such a behaviour strongly depends on the magnetic interactions. Exchange coupling parameters of R–R (A_RR), T–T (A_TT) and R–T (A_RT) have been evaluated from M(T) magnetization curves (2–300 K, 2 T) based on the mean field theory (MFT) calculation. The magnetocaloric effect (MCE) has been estimated from the family of magnetic isotherms. The magnetic entropy indicates relatively small change with the Gd/Y substitution. The value of ΔS_m(T,H) is higher for Gd-rich compounds and, respectively, decreases with Gd/Y substitution.     

Si掺杂的铁磁形状记忆合金Co50Ni21Ga29Six的物性研究

成功生长了Co₅₀Ni₂₁Ga₂₉:Si(x=1,2)单晶样品,对其磁性,马氏体相变及其相关性质进行了细致的测量.发现掺Si成分的单晶具有非常迅速的马氏体相变行为、2.5％的大相变应变、大于100 ppm的磁感生应变和4.5％的相变电阻.进一步研究指出,在CoNiGa合金中掺入适量Si元素,能够降低材料的马氏体相变温度,减小相变热滞后,提高材料的居里温度,并使得磁性原子的磁矩有所降低.尤其重要的是Si元素的添加能够增大材料马氏体的磁晶各向异性能,改善马氏体变体的迁移特性,从而获得更大的磁感生应变. 关键词： 铁磁形状记忆合金 Heusler合金 50Ni₂₁Ga₂₉Si_x')" href="#">Co₅₀Ni₂₁Ga₂₉Si_x     

Crystallography,magnetic properties and magnetocaloric effect in Gd4(BixSb1−x)3 alloys

A study of magnetic and thermal properties has been carried out on the alloys from the Gd₄(Bi_xSb_1−x)₃ series with x=0, 0.25, 0.5, 0.75, and 1. All of the alloys are ferromagnetic below their respective Curie temperatures which vary from 266 K for x=0 to 332 K for x=1.0. The magnetocaloric effect calculated from the temperature and magnetic field dependencies of the magnetization and heat capacity is moderate when compared to that of other materials, which order in the same temperature range. Both the magnetic ordering and the magnetocaloric effect peak temperatures increase nearly linearly with the increasing Bi content. Experimental magnetocaloric effect data obtained from two different measurement techniques are in excellent agreement.     

Magnetic properties of Ni0.8Cu0.2−xGex solid solutions

The results of magnetic measurements performed on Ni_0.8Cu_0.2-xGe_x solid solutions, with x ? 0.10 are reported. The saturation magnetization, Curie temperature and effective nickel moments decrease nearly linear when substituting Cu by Ge. The ferromagnetic resonance measurements show that the g values are not dependent on composition. Finally, the magnetic behaviour of nickel in these solid solutions is analysed.     

X-ray and Mössbauer studies of the Tb<Subscript>0.3</Subscript>Dy<Subscript>0.7</Subscript>Fe<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> system alloys

A complex study of the phase composition, atomic and crystalline structure, magnetic properties, and superfine interactions of the Tb_0.3Dy_0.7Fe_{2 ? x} Co _x system alloys (x = 0?1.3) has been performed. The synthesized alloys are isotypic with the cubic Laves phase (C15 type), their cell parameter monotonically decreases with an increase in the Co content and, hence, the saturation magnetostriction also does. However, the concentration dependences of the Curie temperature, saturation magnetization, and superfine magnetic field strength measured in the Mössbauer experiment display a nonmonotonic (dome-like) character.     

Preparation and investigation of magnetic properties of MnNiTi-substituted strontium hexaferrite nanoparticles

A series of M-type strontium hexaferrite powders with substitution of Mn²⁺, Ni²⁺ and Ti⁴⁺ ions for Fe³⁺ ions according to the formula SrFe₉(Mn_0.5−xNi_xTi_0.5)₃O₁₉, where x ranges from 0 to 0.5 with a step of 0.1, has been prepared via the conventional ceramic method. In order to get nanoparticles, the obtained powders were milled in a high energy SPEX mill for 1 h. XRD investigations of the unmilled and milled powders show that the prepared samples are all single phase hexaferrite. Lattice parameters and mean crystallite sizes of the powders were determined from the XRD data and Scherrer’s formula. Transmission electron microscope (TEM) was used to analyze their structures. Room temperature magnetizations and coercivities of the samples in a magnetic field of 15 kOe have been determined from the hysteresis loops. It was found that magnetizations of the milled samples were smaller than the magnetization of the unmilled samples. This decrease, based on core-shell model, has been attributed to the presence of a magnetically dead layer on the particles’ surface of the milled powders. In addition, the magnetizations of the milled samples decrease with the increase in x value. This decrease has been discussed according to site occupation of the substituted cations on the sublattices. The discussion also supports the increase of lattice parameters and the decrease of Curie temperature as x increases.     

Magnetic properties and magnetocaloric effect of Sr-doped Pr0.7Ca0.3MnO3 compounds

In this work, we pointed out that Sr substitution for Ca leads to modify the magnetic and magnetocaloric properties of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds. Analyzing temperature dependence of magnetization, M(T), proves that the Curie temperature (T_C) increased with increasing Sr content (x); T_C value is found to be 130–260 K for x = 0.0–0.3, respectively. Using the phenomenological model and M(T,H) data measured at several applied magnetic field, the magnetocaloric effect of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds has been investigated through their temperature and magnetic field dependences of magnetic entropy change ΔS_m(T,H) and the change of the specific heat change ΔC_P(T,H). Under an applied magnetic field change of 10 kOe, the maximum value of -ΔS_m is found to be about 3 J/kg·K, and the maximum and minimum values of ΔC_P(T) calculated to be about ±60 J/kg·K for x = 0.3 sample. Additionally, the critical behaviors of Pr_0.7Ca_0.3-xSr_xMnO₃ compounds around their T_C have been also analyzed. Results suggested a coexistence of the ferromagnetic short- and long-range interactions in samples. Moreover, Sr-doping favors establishing the short-range interactions.