Local spin configurations of Fe atoms in the Rh1−x Fex (x=0.1, 0.2, and 0.3) system with competing exchange interactions

The local spin configurations of Fe atoms in the magnetically ordered alloys Rh_1?x Fe_x (x=0.1, 0.2, and 0.3) have been investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the range from 5 K to temperatures of the transition to the paramagnetic state. The measurements in magnetic fields with a strength up to 5 T are carried out at a temperature of 4.2 K. Analysis of the magnetic-hyperfinefield distribution functions demonstrates that Fe atoms form discrete sets of collinear spin configurations corresponding to different net moments of the nearest coordination sphere. The spin structure of the alloys is governed by a random distribution of Fe atoms over the lattice sites and the competition between the Fe-Rh ferromagnetic exchange interaction and the antiferromagnetic interaction of the neighboring Fe atoms. No spin frustration and spin “melting” effects characteristic of spin glasses are revealed in the Rh-Fe alloys.     

Temperature evolution of frustrated spin states in the system with competing exchange interactions. Fe0.65Ni0.35)1−x Mnx (x=0, 0.024, 0.034)

The influence of temperature on the distribution function P(B _hf) of the magnetic hyperfine fields for ⁵⁷Fe in (Fe_0.65Ni_0.35)_1?x Mn_x alloys (x=0, 0.024, 0.034) are investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the temperature interval 5–300 K; in the interval 5–80 K the measurements are performed in a magnetic field of 0.2 T. Anomalies are found in the temperature curves of the intensity of the principal maximum of the functions P(B _hf)[B _hf=30–38 T] and the total (integrated) intensities of the low-field components [B _hf=(4–13) T]. The detected anomalies in the behavior of the total intensities are interpreted as resulting from a change in the balance of competing exchange interactions due to the thermal annihilation of antiferromagnetic Fe-Fe exchange interaction. The emergence of strong satellite lines in the interval B _hf=20–29 T in Mn-doped alloys is attributed to reorientation of the spins of Fe atoms under the influence of strong antiferromagnetic Mn-Fe exchange interaction.     

Thermal destruction of antiferromagnetic Fe-Fe exchange bonds and mechanism of the transition to the spin-glass state in (Fe0.65Ni0.35)1−x Mnx systems with antiferromagnetic competing exchange interactions

The thermal evolution of the competition between the ferro-and antiferromagnetic exchange interactions in (Fe_0.65Ni_0.35)_1?x Mn_x alloys, which display different magnetic properties, depending on composition and temperature, is investigated. The distribution functions of the magnetic hyperfine fields P(B _hf) for ⁵⁷Fe are determined by Mössbauer spectroscopy in the temperature range 5–300 K for the alloys with x=0, 0.024, 0.082, 0.136, 0.195, and 0.252. The temperature dependence of the integrated intensity I _s (T) is analyzed for the low-and high-field portions of P(B _hf). The features found in the behavior of I _s (T) are interpreted as results of variation of the ratio between the competing exchange interactions of different signs as a result of the thermal destruction of antiferromagnetic Fe-Fe exchange bonds. It is shown that the changes in the spin structure in the low-temperature range are due to the thermal destruction of Fe-Fe exchange bonds. One of the consequences of this destruction is “reentrance” (an increase in the hyperfine field with increasing temperature for some of the Fe atoms). The relationship between the thermal destruction of Fe-Fe exchange bonds and the magnetic transitions of the Fe-Ni-Mn system to the spin-glass state is considered.     

Electronic structures and local magnetic moments in ferromagnetic and antiferromagnetic FexRh1−x alloys

Ground-state magnetic properties of ordered FeRh alloys are discussed by using the realistic canonical d-band model within the Hartree-Fock and coherent potential approximations. Local magnetic moments of Fe and Rh atoms in ferromagnetic and antiferromagnetic Fe_xRh_1-x alloys are computed as a function of x, the Fe concentration. Calculated results are in good agreement with the neutron-diffraction data. The band-energy calculation indicates that in Fe-rich alloys excess Fe atoms substituted on Rh sites having larger magnetic moments than Rh atoms, play an important role in the antiferromagnetic to ferromagnetic transition observed at low temperatures.     

Origin of the strong influence of rhodium on the Curie temperature of Pd–Fe alloys: the spin reorientation in (Pd100−xRhx)90Fe10 alloys

The hyperfine field distributions and the local spin configurations for Fe atoms in the (Pd_100−xRh_x)₉₀Fe₁₀ alloys for x=0, 10 and 20 are investigated by the Mössbauer spectroscopy technique. It was found that the anomalous behavior of T_C in these alloys is attributable to the spin reorientation in some part of Fe atoms with the formation of local antiferromagnetic spin configurations.     

The hyperfine magnetic field at57Fe and181Ta in Hf(Fe1−x Co x )2 system

The hyperfine magnetic field at⁵⁷Fe in the ferromagnetic Laves compounds Hf(Fe_1?x Co _x )₂ was measured by the Mössbauer effect method. The substitution of Fe atoms by Co atoms induces a gradual change ofB _hf(Fe) and a decrease in the magnetic moment values in Fe?Co sublattice. The perturbed angular correlation measurements of¹⁸¹Ta were carried out forX=0,X=0.1,X=0.55 at 300 K, andX=0.4 atT=400°C. An abrupt change ofB _hf (Ta) in 0<X<0.1 was observed.     

Magnetic ordering of Fe atoms in icosahedral Al70−x BxPd30−y Fey quasicrystals

Novel icosahedral quasicrystals, in which Fe atoms possess a magnetic moment, have been found in Al_70?x B_xPd_30?y Fe_y compounds with 5<x<10 and 10<y<20. The compounds have ferromagnetic properties, and their Curie temperature ranges between 280 and 340 K, the saturation magnetization σ _s(5 K)≈7.5 emu/g. It follows from Mössbauer spectra that only a fraction of Fe atoms (12 to 15%) are magnetically ordered at 4.2 K, and the mean saturation field 〈H _hf〉=96 kOe. The isomer shift values confirm that the atomic volume of magnetic Fe sites is larger than that of nonmagnetic Fe sites. The magnetic properties of these quasicrystals can be interpreted in terms of large magnetic clusters with a size of 185 to 290 Å. This size correspond to about 4×10⁴ “unit cells,” hence the magnetic state can be described in terms of bulk parameters. The localized magnetic moment of Fe atoms is tentatively ascribed to bonding between Fe and B, similarly to that in the amorphous Fe_～50B_～50 alloy.     

Ab-initio investigation of electronic properties and magnetism of half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In)

The electronic structures and magnetism of the half-Heusler alloys XCrAl (X=Fe, Co, Ni) and NiCrZ (Z=Al, Ga, In) have been investigated to search for new candidate half-metallic materials. Here, we predict that NiCrAl, and NiCrGa and NiCrIn are possible half-metals with an energy gap in the minority spin and a completely spin polarization at the Fermi level. The energy gap can be attributed to the covalent hybridization between the d states of the Ni and Cr atoms, which leads to the formation of bonding and antibonding peaks with a gap in between them. Their total magnetic moments are 1μ_B per unit cell; agree with the Slater-Pauling rule. The partial moment of Cr is largest in NiCrZ alloys and moments of Ni and Al are in antiferromagnetic alignment with Cr. Meanwhile, it is also found that FeCrAl is a normal ferromagnetic metal with a magnetic moment of 0.25μ_B per unit cell and CoCrAl is a semi-metal and non-magnetic.     

Magnetic order in palladium-based Heusler alloys Part I: Pd2MnIn1−xSnx and Pd2MnSn1−xSbx

Magnetization, susceptibility, X-ray and neutron diffraction measurements have been made on the two series of alloys Pd₂MnIn_1?xSn_x and Pd₂MnSn_1?xSb_x, for 0 ? x ? 1. All were single phase and were chemically ordered intermetallic compounds with the Heusler L2₁ structure in which the Mn atoms occupy an f.c.c. sub-lattice. At all compositions the alloys were magnetically ordered with a moment of ～4.3 μ_B located at the Mn sites. At the In-rich end the magnetic order is antiferromagnetic f.c.c. type 2. As Sn is increasingly substituted for In there is a change in magnetic order first to antiferromagnetic f.c.c. type 3A and then to ferromagnetism. All the alloys in the Sn/Sb series are ferromagnetic and in both series there is an increase in the ferromagnetic exchange interactions with increasing electron concentration.     

First principles study the ferromagnetic properties and electronic structure of boron doped ZnSe

Using the full-potential linearized augmented plane wave method with generalized gradient approximation, the magnetic properties and the electronic structure of the boron-doped ZnSe (zinc blende phase) are investigated. Spin polarization calculations show the magnetic moment of the 64-atoms supercell containing one B_Se (B_Zn) is 3.00 (0.015) μ_B. The density of states indicates the magnetic moments of the B_Se doped configuration mainly come from the doped boron atoms and a few from its neighboring zinc atoms. The ferromagnetic and antiferromagnetic calculations for several doped configurations suggest B_Se could induce stable ferromagnetic ground state in ZnSe hosts and ferromagnetic couplings exist between the doped boron atoms. Electronic structures show that B_Se is p-type ferromagnetic semiconductor and hole-mediated double exchange is responsible for the ferromagnetism, while the B_Zn doped configuration is n-type semiconductor. Relative shallow acceptor and donor levels indicate boron-doped ZnSe is ionized easily at working temperatures.     

Magnetic hyperfine fields of (Nd2Fe1-xCox)14B AT x = 0.25 between 100 and 780 K

The ⁵⁷Fe Mössbauer spectra are recorded in Nd₂(Fe_1-xCo_x)₁₄B at x = 0.25 in the temperature range 100 to 780 K. T_c the Curie temperature, B̄_hf, the magnetic hyperfine field average over various Fe nuclei of the unit cell and its temperature coefficient α(B̄_hf) in the vicinity of 300 K are found to be 760(5) K, 34.0(3) T and -0.08(1)% K^-1, respectively. The magnetic moment at Fe atoms is estimated to increase up to 12% as a result of the partial substitution by Co atoms. The dependence of the fields upon temperature is observed to be least at the j₂ and k₂ sites as compared to the other sites of Fe. The results for the variation of B_hf at all of the six sites of Fe with respect to temperature are given. A site preference of Fe atoms for the j₂ sites is observed.     

Measurements of the hyperfine magnetic fields at Ta and Fe in the Laves compounds (Zrx Hf1−x)Fe2 for 0≤x≤1

The hyperfine magnetic fields at¹⁸¹Ta and⁵⁷Fe in the ferromagnetic Laves intermetallic compounds (Zr_xHf_1?x)Fe₂ (0≤x≤1) have been measured by the methods of TDPAC and Mössbauer effect, respectively, and shown to be practically independent of x at x≥0.4. An average value B_hf (Ta)=?6.52 T at 300 K was obtained for samples with x≥0.4, and ?14.2 T for pure HfFe₂ in the hexagonal C14 modification. For 0hf(Ta) in (Zr_0.9 Hf_0.1)Fe₂ from that for B_hf (Fe) and the bulk magnetization was confirmed, studied in detail, and shown to exist for all x≥0.4. The temperature dependence of B_hf(Ta) in HfFe₂ was close to that of B_hf (Fe).     

Hyperfine fields and Fe magnetic moments in Fe−Ni invar alloys

Mössbauer spectra of Fe_1?x Ni _x withx=0.40, 0.35 and 0.32 were taken at various temperatures and fitted withB _hf distributions. TheP(B _hf) curves generally show a peak and a low-field tail. The peakB ^* and the average \(\bar B\) were obtained in theT→0 limit. Fe moments were deduced from these data with help of a semiempirical equation. While the average \(\bar \mu _{Fe} \) decreases withx (invar anomaly), a large fraction of Fe atoms retain the strong moment (≈ 2.7 μ_B) typical of Ni-rich alloys. This result is consistent with a two-states model for invar.     

A DFT study of the electronic and magnetic properties of Fe2MnSi1−xGex alloys

We performed density functional theory (DFT) calculations to study the structural, electronic and magnetic properties of Fe₂MnSi_1−xGe_x alloys (x=0, 0.25, 0.50, 0.75, and 1.00). The lattice constant is found to increase linearly as a function of Ge concentration with a decrease in the formation energy. The total magnetic moment is found to be 3 μ_B for all alloys with the most contribution from Mn local magnetic moments. Iron atoms, however, exhibit much smaller spin moments about 10% of the bulk value. It seems that due to the proximity of Fe, magnetic moments have been induced on the sp atoms, which couple antiferromagnetically with Fe and Mn spin moments. Although, the band gap remains almost constant (0.5 eV), the spin–flip gap decreases as a function of x.     

Muon hyperfine fields in iron and its dilute alloys

The temperature dependence (240 to 633 K) of the interstitial magnetic field, B_μ, as determined by the rotation of the spin of the μ⁺, has been measured for dilute polycrystalline iron alloys with Mo, Ti and Nb additions. In all cases the behaviours differ from one another and from the Fe(A1) alloys previously studied. B_μ, which is negative with respect to the magnetization, is increased in magnitude by A1 and Mo, and decreased greatly by Ti. The addition of Nb creates a two- phase alloy from which we can assess the role of heterogeneity and/or strain on B_μ in iron. If the temperature dependence of the hyperfine field B_hf extracted from B_μ for Fe(Mo) alloys is interpreted on the model previously used to discuss the Fe(A1) data, we would conclude that the muon is attracted to the Mo atom while repelled by the A1 atoms as the temperature decreases. Measurements giving room temperature values of B_μ for iron alloys with Mn, Cr, V and W taken after annealing above the recrystallization temperature are also reported.     

First-principles study of structural, electronic and magnetic properties in Cd1−xFexS diluted magnetic semiconductors

In this paper, we report theoretical investigations of structural, electronic and magnetic properties of ordered dilute ferromagnetic semiconductors Cd_1−xFe_xS with x=0.25, 0.5 and 0.75 in zinc blende (B3) phase using all-electron full-potential linear muffin tin orbital (FP-LMTO) calculations within the density functional theory and the generalized gradient approximation. The analysis of band structures, density of states, total energy, exchange interactions and magnetic moments reveals that both the alloys may exhibit a half-metallic ferromagnetism character. The value of calculated magnetic moment per Fe impurity atom is found to be 4 μ_B. Moreover, we found that p-d hybridization reduces the local magnetic moment of Fe from its free space charge value of 4 μ_B and produces small local magnetic moments on Cd and S sites.     

亚铁磁Heusler合金Mn2CoGa和Mn2CoAl掺杂Cr,Fe和Co的局域铁磁结构

通过实验和计算的方法研究了Mn₂CoM_xGa_1-x 和Mn₂CoM_xAl_1-x (M=Cr, Fe, Co)掺杂系列合金样品. 研究发现, 在共价作用的影响下, Fe和Co原子占A位, 使被取代的MnA (-2.1 μ_B)变成MnD (3.2 μ_B), 在最近邻的强交换作用下亚铁磁基体中形成了MnB-CoC-MnD局域铁磁性结构, 使分子磁矩的增量最高可达6.18 μ_B. Fe, Co 掺杂后建立同样的局域铁磁结构, 居里温度的变化趋势却不同. 实验观察到Mn₂Co_1+xAl_1-x中掺杂容忍度高达x=0.64, 远高于在Mn₂CoGa中(x=0.36)的结果; 以及随着Al的减少, 合金由B2有序向A2混乱转变等现象, 为共价作用对合金结构稳定的影响提供了证据. 磁测量中发现Cr掺杂后磁矩增量高达3.65 μ_B以及居里温度快速上升的反常现象, 意味着对占位规则的违背.     

Influence of the local environment on the hyperfine interactions in Zr(Fe1-xCox)2 compounds

Ferromagnetic Laves phase compounds Zr(Fe_1-xCo_x)₂ have been investigated by means of the Mössbauer effect (⁵⁷Fe) and by the time-dependent perturbed angular correlation of \gamma -rays (¹⁸¹Ta) technique. It has been concluded from ME experiments that by exchange of Fe by Co in the nearest neighbour shell of the nuclear probe the hyperfine magnetic field acting on ⁵⁷Fe decreases by 10--12 kG. The analysis of the TDPAC experiments revealed that two different hyperfine magnetic fields: B₁ ^hf(Ta)~ 61 kG and B₂ ^hf(Ta)~ 88 kG act on the ¹⁸¹Ta nuclei. Both have a negative sign.     

Mössbauer study of magnetic Fe/FeSi multilayers

Many useful properties of magnetic multilayers depend on the coupling between the ferromagnetic layers. The coupling often oscillates with the thickness of non-magnetic spacer layers: it is ferro- or antiferromagnetic or even non-collinear near a critical thickness. We investigated the magnetron-sputtered Fe/FeSi multilayers with spacer thickness around 1.7 nm by means of Conversion Electron Mössbauer Spectroscopy with oblique incidence of the γ beam in order to gain information on the orientation of the local magnetic moments in the multilayer plane. The results show that the local moments make an angle of 45°–50° with the direction of the remanent magnetization. This is consistent with strong biquadratic coupling which in turn is expected at this spacer thickness from our magnetic measurements. An analysis of the distribution ofB _hf corresponding to different numbers of n.n. Si atoms in the bcc Fe structure points to weak diffusion of Si through the Fe/FeSi interface characterized by a diffusion length of about twice the substrate roughness.