Hyperfine fields at sp sites in Clb Heusler alloys

Hyperfine fields have been measured at Cd, Sn and Sb sites in several Ni, Rh, Ir and Pt-based Heusler alloys. The Cd fields at 77 K were found to be ?95 k0e, ?108(4) k04, ±166(5) k0e and +196(9) k0e in RhMnSb, IrMnSn, IrMnSb and PtMnGa, respectively. Sn-site fields were found to be ±53(5) k0e and ±62(5) k0e in NiMnSb and PtMnSb, respectively, and the Sb-site fields, +276(5) k0e, +65(5) k0e and +210(5) k0e in NiMnSb, IrMnSb and PtMnSb, respectively. Results are discussed in terms of 5sp site hyperfine field systematics in Cl_b Heusler alloys.     

Hyperfine magnetic fields in substituted Finemet alloys

Transmission Mössbauer spectroscopy was used to determine the hyperfine fields of Finemet-type alloys in form of ribbons, substituted alternatively by Mn, Ni, Co, Al, Zn, V or Ge of various concentration. The comparative analysis of magnetic hyperfine fields was carried out which enabled to understand the role of added elements in as-quenched as well as annealed samples. Moreover, the influence of the substitution on the mean direction of the local hyperfine magnetic field was examined.     

Hyperfine magnetic fields in Fe−Co alloys and their tempera ture dependences

We obtained⁵⁷Fe hyperfine field parameters from Fe₁−x-Co _x alloys (0≤x≤0.6) from 77 K to 900 K. We first discuss the origin of the low temperature hyperfine fields in terms of the 3d and 4s electrons at⁵⁷Fe atoms. The⁵⁷Fe hyperfine magnetic field (hmf) of Fe-Co alloys depends more weakly on temperature than the hmf of pure Fe. This temperature dependence occurs because the alignment of the magnetic moments at both the Fe atoms and at the Co atoms depend on temperature in the same way as the bulk magnetization of Fe-Co alloys.     

Hyperfine fields and the polarization of conduction electrons in semimetallic Heusler alloys

The distribution of hyperfine fields in half-metallic Heusler alloys is measured using the nuclear spin-echo method. The results from studying a great many series of samples of different composition reveal the enormous problems in obtaining materials with increased polarization of conduction electrons via the usual method of varying their composition. Other alternatives are proposed.     

Hyperfine fields in a new Heusler alloy Mn2CoSn

A new Heusler alloy Mn₂CoSn has been obtained. The distribution of hyperfine fields in Mn₂CoSn and Mn₂CoSn alloys by nuclear spin echo method has been investigated. The conclusion concerning ferrimagnetic structure of Mn₂CoSn alloy has been drawn.     

Hyperfine magnetic field measurements in Heusler alloys Ni2MnGa,Pd2MnSn,and Ru2FeSn

Hmf values are reported for Fe-57 in Ni₂MnGa, and for Cd-111, Fe-57, and Sn-119 in Pd₂MnSn and Ru₂FeSn.     

Magnetic hyperfine fields in Heusler alloys Co YZ (Y=Ti,Zr; Z=Al,Ga,Sn)

Magnetic hyperfine fields (mhf) acting on Ta at the Ti and Zr sites have been measured in Heusler alloys Co₂TiAl(Ga,Sn) and Co₂ZrAl(Sn) by the TDPAC technique utilizing the 133–482 keV gamma cascade in¹⁸¹Hf. Curie temperatures of all the alloys have also been measured using a vibrating sample magnetometer. Present data together with the existing results on the Co₂HfAl(Ga,Sn) are discussed and compared with the mhf systematics in Heusler alloys.work partially supported by CNEN and CNPq     

Hyperfine fields on59Co in ReCo2

We report⁵⁷Fe Mössbauer measurements in the diluted antiferromagnetic (AF) Fe_xZn_1?xF₂ withx=0.25 at temperatures between 4.2 and 28 K. DC susceptibility measurements show a spin-glass (SG) phase at low temperatures forx?0.3. Our Mössbauer spectra show a competitive coexistence of an SG phase and AF order. We propose an interpretation in terms of clusters in the AF order and some spins exhibiting SG behavior.     

Hyperfine fields of 5sp shell impurities substituting Sb in the Heusler alloys Pd2MnSb and PdMnSb

Measurements of the hyperfine magnetic fields B_hf of Te and I impurities substituting Sb in the Heusler alloys Pd₂MnSb and PdMnSb clearly establish that the curve of B_hf versus impurity atomic number is shifted to the right by about 1 unit of atomic number for PdMnSb relative to Pd₂MnSb. This phenomenon, and the general shape of the curve can be understood in terms of the conduction electron polarization model developed by Blandin and Campbell.     

Observation of magnetic splitting in XPS MnL-spectra of Co2MnSn and Pd2MnSn Heusler alloys

The XPS MnL-spectra of Co₂MnSn, a nearly half-metallic ferromagnet (HMF) and Pd₂MnSn were investigated. The most drastical feature of the spectra observed is the well-defined magnetic splitting of the Mn 2p _3/2 , 2p _1/2 lines. This gives direct evidence of the existence of well-defined local magnetic moments in Heusler alloys in comparison with other itinerant-electron ferromagnets. The calculations of Mn2p XPS spectra of these materials were carried out using a fully relativistic generalization of the one-step model of photoemission and show excellent agreement with experiment. Received: 31 October 1997 / Received in final form: 28 November 1997 / Accepted: 18 December 1997     

Hyperfine magnetic fields at rare-earth elements in ferromagnetic transition metals

Hyperfine magnetic fields for such probes as:¹⁵²SmFe,¹⁵²SmCo,¹⁵²SmNi,¹⁵⁵GdFe,¹⁷²YbFe,¹⁷²YbCo and¹⁷²YbNi have been measured using PAC method. The quantitative analysis of components of these fields has been also performed.     

Hyperfine fields at Ce in GdAl2 and DyAl2

The local fields at¹⁴⁰Ce in the cubic intermetallic compounds GdAl₂ and DyAl₂ have been measured with the DPAC method. At our lowest temperatures we obtainB _eff (30K)=54(2) T for GdAl₂ andB _eff(12.5K)=27(1) T for DyAl₂ which are considerably lower than the hyperfine field of the free Ce³⁺ ion (183 T). The (Ce)GdAl₂ field is quantitatively explained by a cubic crystal field splitting of 4f states but for DyAl₂ additional effects are discussed.     

Electrical properties of ferromagnetic Ni2MnGa and Co2CrGa Heusler alloys

The electrical properties of ferromagnetic Ni₂MnGa and Co₂CrGa Heusler alloys are measured in the temperature range 4–900 K. The effect of the energy gap near the Fermi level in the electronic spectrum on the behavior of electrical resistivity and absolute differential thermopower is discussed.     

Hyperfine fields in iron dilute alloys and internal oxidation

AnFe-V 2.5 at% foil was annealed at various temperatures in the range from 120°C to 1000° \(\bar C\) for 10 min and analysed by Transmission Mössbauer Spectroscopy (TMS) and Conversion Electron Mössbauer Spectroscopy (CEMS) after each thermal process. A computational method to fit the spectra to obtain a parameter related to the concentration of the alloy was studied and applied to the data. No surprising effects were found on the bulk measurements (TMS), but there is a clear decrease of the alloy concentration in the 550°C to 700°C annealing temperature range, observed for the surface analysis (CEMS measurements). The phenomenon was attributed to the preferential internal oxidation of vanadium atoms in this range of temperature. Probably some vanadium oxide decomposition occurs at higher temperatures, recovering the original state of the sample.