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.     

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.     

Mössbauer measurement of the hyperfine magnetic field AT sp site in Heusler alloys Rh2 Mn Z (Z=In and Sb)

We have investigated the systematics of hyperfine magnetic field on a fixed probe at the Z-site in Heusler alloys Rh₂MnZ as the valence of Z (sp element) is varied. The hmf on¹¹⁹Sn in Rh₂MnIn_.98 ¹¹⁹Sn₀₂ has been measured at 293K and 77K. In Rh₂Mn_1.12Sb_.86 ¹¹⁹Sn_.02 the hmf on¹²¹Sb has been measured at 77 K, and on¹¹⁹Sn at 293 K and 77 K. The results are compared with the hmf on¹¹⁹Sn in Rh₂Mn Ge_.98 ¹¹⁹Sn_.02 Rh₂Mn Sn, and Rh₂Mn Pb_.98 ¹¹⁹Sn_.02.Supported by the University Research Council, University of CincinnatiSupported by the Natural Sciences and Engineering Research Council of Canada     

High-pressure Mössbauer study of the Curie temperatures and transferred hyperfine fields at 151Eu and substitutional 119Sn in EuS and EuSe

Changes with pressures up to 55 kbar of the Curie temperatures and the ¹⁵¹Eu and ¹¹⁹Sn hyperfine parameters were investigated in the europium monochalcogenides EuS and EuSe doped with small amounts of substitutional Sn²⁺. In both (Eu_1-xSn_x) S and (Eu_1-xSn_x) Se with 0.01 ≤x ≤ 0.05, the observed strong increase of T_c is correlated w ith a strong increase of the transferred hyperfine fields. EuSe is found to order ferromagnetically above 14 kbar.     

Magnetic order in palladium-based heusler alloys: Part 2: Pd2MnIn1−ySby

Magnetization, susceptibility, X-ray and neutron-diffraction measurements have been on the Heusler alloy series Pd₂MnIn_1?ySb_y, for 0 < y < 1. All the alloys were chemically and magnetically ordered with a moment of ?4.2μ_B located at the Mn sites. Their magnetic structures change from antiferromagnetic fcc type 2 at the In rich end, to antiferromagnetic fcc type 3A and then to ferromagnetism as the Sb content is increased. The results closely parallel those already reported on the isostructural series Pd₂MnIn_1-xSn_x and Pd₂MnSn_1-xSb_x with the changes in magnetic structures o ccurring at the same conduction electron concentrations. The results strongly support the postulate that the exchange interactions in Heusler alloys are essentially dependent upon the conduction electron concentration. The correlation between the data and an indirect double resonance exchange coupling mechanism is discussed.     

A TIN-119 Mössbauer and electrical conductivity study of the system SnxGe1-xSe (0 ⩽ x ⩽ 1)

¹¹⁹Sn Mössbauer parameters and electrical conductivity data for phases in the system Sn_xGe_1-xSe (0 ? x ? 1) are reported. The Mössbauer data for the material Sn_0.8Ge_0.2Se show that the electron distribution around the Sn at this composition is anomalous. There is, however, little indication of the presence of such an anomaly in the electrical conductivity and Hall Effect data. The implications of these observations are discussed.     

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.     

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.     

Magnetic hyperfine structure of 119Sn in ferromagnetic Pd2MnSb

A magnetic hyperfine field of H = + 210 ± 5 kOe has been observed at Sn in Pd₂MnSb_0.99Sn_0.01 by Mössbauer spectroscopy on ¹¹⁹Sn. The significance of this measurement with respect to other hyperfine fields and theoretical calculations is discussed.     

Structural and Magnetic Properties of NiFe2−2xSnxCuxO4

The substituted nickel ferrite (NiFe_2−2xSn_xCu_xO₄, x=0, 0.1, 0.2, 0.3) was prepared by the conventional ceramic method. The effect of substitution of Fe³⁺ ions by Sn⁴⁺ and Cu²⁺ cations on the structural and magnetic properties of the ferrite was studied by means of ⁵⁷Fe Mössbauer spectroscopy, alternating gradient force magnetometry (AGFM) and Faraday balance. Whereas undoped NiFe₂O₄ adopts a fully inverse spinel structure of the type (Fe)[NiFe]O₄, Sn⁴⁺ and Cu²⁺ cations tend to occupy octahedral positions in the structure of the substituted ferrite. Based on the results of Mössbauer spectroscopic measurements, the crystal-chemical formula of the substituted ferrite may be written as (Fe)[NiFe_1−2xSn_xCu_x]O₄, where parentheses and square brackets enclose cations in tetrahedral (A) and octahedral [B] coordination, respectively. The Néel temperature and the saturation magnetization values of the NiFe_2−2xSn_xCu_xO₄ samples were found to decrease with increasing degree of substitution (x). The variation of the saturation magnetization with x measured using the AGFM method and that calculated on the basis of the Mössbauer spectroscopic measurements are in qualitative agreement.     

Magnetic properties of TbMn6Sn6-xGax (x=0.0－1.2) compounds

Effects of Ga substitution for Sn on the structure and magnetic properties of TbMn₆Sn_6-xGa_x (x=0.0－1.2) compounds have been investigated by means of x-ray diffraction, magnetization measurement and ¹¹⁹Sn M?ssbauer spectroscopy. The substitution of Ga for Sn results in a decrease in lattice constants and unit-cell volumes. The magnetic ordering temperature decreases monotonically with increasing Ga content from 423 K for x=0.0 to 390 K for x=1.2. At room temperature, the easy magnetization direction changes from the c-axis to the ab-plane. This variation implies that the substitution of Ga for Sn leads to a decrease in the c-axis anisotropy of the Tb sublattice. An increase in the non-magnetic Ga concentration results in a monotonic decrease of the spontaneous magnetization M_s at room temperature. Since there are three non-equivalent Sn sites, 2c (0.33, 0.67,0), 2d (0.33, 0.67,0.5) and 2e (0,0,0.34) in the TbMn₆Sn_6-xGa_x compounds, the ¹¹⁹Sn M?ssbauer spectra of the TbMn₆Sn₆ and TbMn₆Sn_5.4Ga_0.6 compounds can be fitted by three sextets. The hyperfine fields (HFs) decrease in the order of HF(2d)>HF(2e)>HF(2c), which is in agreement with the magnetic structure.     

Spin-disorder resistivity in Ni2Mn(Sn1−xInx) heusler alloys

Electrical resistivity measurements have been performed on Ni₂Mn(Sn_1?xIn_x) Heusler alloys, where x = 0, 0.02, 0.05, 0.10 and 0.15, in the temperature range of 4–300 K. The experimental data clearly show the existence of two distinct kinds of resistivity behaviour, both described by an aTⁿ law, for 7 ? T ? 20 K. Between 170 and 300 K the data are well described by an AT + BT² phenomenological fit, and the results obtained are in good agreement with an interpretation based on electron-phonon and spin-disorder scattering.     

A 57Fe and 119Sn Mössbauer study of BaFe4Sn2O11

The Mössbauer spectrum of BaFe₄Sn₂O₁₁ has been recorded for both ⁵⁷Fe and ¹¹⁹Sn isotopes at a variety of temperatures. In the paramagnetic state the ⁵⁷Fe spectra are interpreted in terms of three iron environments. Magnetic ordering begins at 77 K and is virtually complete by 4.2 K to give an average magnetic hyperfine field of 504 kG. The ¹¹⁹Sn spectra also reflect the magnetic ordering and a magnetic hyperfine field of 45 kG is transferred to the tin nuclei.     

Magnetism of Cu2(Mn1−xNix)Sn Heusler alloys

New mixed Heusler alloys of the system Cu₂(Mn_1?xNi_x)Sn were prepared with x = 0–1. Magnetic measurements in the ferromagnetic region were undertaken. For manganese, the only atom displaying a magnetic moment in this row of Heusler alloys, 4μ_B was found, deviations were due to the degree of order. Measurements in the paramagnetic region were not possible because of phase transitions on heating leading to polyphase samples. The critical concentration of magnetic ions was estimated to 13 at.% and compared with models given by Duff and Cannella [6]. With the same plot the Curie point for Cu₂MnSn could be determined (630 K).     

Mössbauereffekt- und Magnetisierungsmessungen an EuxYb1-xSn3

Mössbauer effect and magnetization measurements were performed in the intermetallic system Eu_xYb_1-xSn₃ for 0≦x≦100 at%. The magnetic behavior of the system depends only on the Eu concentration. For allx the system has the same crystal structure (fcc) and is ordered antiferromagnetically. The dependence of the paramagnetic Curie temperature, the ordering temperature, and the hyperfine fields at the Sn and Eu sites on the Eu concentration are discussed in the frame of the RKKY theory.     

119Sn Mössbauer spectroscopy of U x Th1−x CoSn and UCoAl1−x Sn x

Magnetization and¹¹⁹Sn Mössbauer spectroscopy studies were performed on two pseudoternary systems, namely U _x Th_1?x CoSn and UCoAl_1?x Sn _x . Magnetic hyperfine fields on¹¹⁹Sn nuclei were found to be due to local surrounding of U atoms which carry magnetic moments. In pure UCoSn the valuesB _hf=8.66 T and μ_∪ satisfy the relationB _hf=6.75 μ_B found for a number of UTX compounds studied. Local surrounding effects are indicated by multicomponent spectra obtained for the two pseudoternary series.     

Structure and Mössbauer effect studies of Y2Sn2-xFexO7-δ pyrochlores

Y₂Sn_2-x Fe _x O_7- pyrochlores were studied by means of X-ray diffraction,¹¹⁹Sn and⁵⁷Fe Mössbauer spectroscopy. The single phase Y₂Sn_2-x Fe_xO_7- Y pyrochlores up tox=0.8 were produced by the chemical coprecipitation method. The quadrupole splittings of¹¹⁹Sn decrease linearly with increasing iron content. The⁵⁷Fe Mössbauer spectra forx=0.6 and 0.8 both are composed of a sextet and two doublets, indicating that some Fe³⁺ ion environments in the pyrochlores are magnetically ordered. The magnetic hyperfine splitting disappears in the sample withx= 1.0, which contains a second phase.This work was partially supported by the National Natural Science Foundation of PR China.     

Effet Mössbauer sur les noyaux d'impuretes 119Sn4+ dans la matrice de VO2

The phase transition in VO₂ doped with 0.16 at.% Sn⁴⁺ was investigated by Mössbauer spectroscopy of ¹¹⁹Sn. Hyperfine magnetic fields were observed on ¹¹⁹Sn nuclei below the transition temperature. At 77 K the maximum hyperfine magnetic field was found to be H(0)_{77 K} = 120 ± 10 kOe The results obtained are discussed in terms of fine antiferromagnetic particles.     

Magnetic ordering in the system Co2-xNix TiSn studied by 119Sn-Mössbauer spectroscopy and magnetization measurements

Magnetization and Mössbauer with ¹¹⁹Sn measurements have been performed in the system Co_2-xNi_xTiSn. Transferred field distribution at the Sn site is very well consistent with the assumption, that only the nearest magnetic neighbours contribute to the field in contradiction with the Blandin-Campbell model, where the long range spin polarization of the conduction band occurs.     

Hyperfine interactions and dynamics characteristics of 119Sn in xSnO2-(1-x)α-Fe2O3 nanoparticle system

The hyperfine interactions and dynamics aspects in nanoparticles system of the xSnO₂-(1-x)α-Fe₂O₃ (x = 0.0–1.0) have been investigated by ¹¹⁹Sn-Mössbauer and XRD techniques. The change revealed by the XRD (XRDSs) and Mössbauer spectra (MSs) vs. x was discussed in terms of the phase and lattice-dynamics changes. The evidences of the triple hyperfine magnetic fields’ distributions (MHFDs) and their dependencies x (<0.175) are discussed taking into account the super-transferred hyperfine interactions (STHI), the local disorder Sn^4?+?/Fe^3?+? around the tin isotope probe and the reduced dimension effect.