Hyperfine Interactions of 8Li in Ferromagnetic Single Crystal Fe

The hyperfine interactions of ⁸Li implanted in single crystal Fe have been studied using the β-NMR technique. One kind of hyperfine field B _hf was found. Since no dipolar field was observed, ⁸Li nuclei are suggested to sit in substitutional sites. The B _hf and the spin-lattice relaxation time T ₁ were observed as functions of temperature. The experimental B _hf and T ₁ were compared with the theoretical predictions from the first principles KKR-band-structure calculations. While predicted B _hf for the substitutional site is consistent with the experiment, predicted T ₁ cannot reproduce the experiment well. This revised version was published online in September 2006 with corrections to the Cover Date.     

Mössbauer spectroscopical investigation of the exchange biased Fe/MnF2 interface

Two different Fe/MnF₂ samples have been prepared by e-beam evaporation on MgO(001) substrates. The Fe layer in the samples includes a 10 Å thick ⁵⁷Fe probe layer either at the Fe/MnF₂ interface (interface sample) or 35 Å away from the interface (center sample). The samples are characterized by X-ray diffraction, conversion electron Mössbauer spectroscopy (CEMS) and SQUID magnetometry. ⁵⁷Fe CEMS has been employed to study the depth dependent hyperfine interactions in Fe/MnF₂ as a function of temperature between 18 K to 300 K. The hyperfine field B _hf has been obtained for the interfacial and off-interfacial ⁵⁷Fe layers. At the interface, besides B _hf of bcc-Fe, the presence of a component with a distribution P(B _hf ) is observed. The latter is assigned to interfacial ⁵⁷Fe atoms, indicating some (～15%, equivalent to ～1 Fe atomic layer) intermixing at the Fe/MnF₂ interface and a decrease of the average hf > by 21%. The influence of the interface disappears as the ⁵⁷Fe probe layer is placed away from the interface. The temperature dependence of the average hf > of the interface has been measured. The Fe spins, at remanence, are found to lie in the film plane.     

Local spin correlations in partially frustrated amorphous Fe-Mn

Mössbauer measurements in a-(Fe_0.765Mn_0.235)₇₈Sn₂Si₆B₁₄ have been performed with⁵⁷Fe and¹¹⁹Sn. Both hyperfine fields show a kink near 70 K, indicating a freezing of the transverse spins. The ratio of the two hyperfine fields contains information about the correlation of the transverse spins. The ratioB _hf(Sn)/B _hf(Fe) stays constant aboveT _xy and rises belowT _xy . This indicates an alignment of the transverse spins on a local scale, as was also found inAuFe and a-FeZr.     

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).     

57Fe/Co Multilayers Investigated by CEMS and Nuclear Resonance Reflectivity Time Spectra Using Grazing Incident SR

[Fe₆Co₃] and [Fe₅Co₅] superlattices have been studied by CEMS and time dependent nuclear resonance scattering in grazing incidence Bragg reflection geometry. CEMS shows hyperfine fields (B _hf) between 33 T and 37 T. The time spectra of reflectivity allows us to separate contributions from different ⁵⁷Fe monolayers in a bilayer. Contrary to our expectations the largest field is in the center of the Fe layers. The spontaneous orientation of B _hf is along [1 1 0] in the layer plane. This revised version was published online in September 2006 with corrections to the Cover Date.     

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.     

Negative muon spin precession in ferromagnetic iron and the hyperfine anomaly

The hyperfine field (B _μ ^hf ) at the negative muon μ⁻ in ferromagnetic iron was investigated by means of the zero-field μ⁻ spin precession technique. In the temperature range 320–690 K,B _μ ^hf for μ⁻ Fe departs from the magnetization curve of pure iron in the same way as the hyperfine field seen by a⁵⁵Mn impurity in dilute MnFe measured by NMR. The hyperfine anomaly for μ⁻ Fe relative to dilute (1.5 at.%)⁵⁵Mn in iron is found to be −0.9(3)% and temperature independent over the temperature range investigated.     

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.     

The radial dependence of the magnetic hyperfine field for Sn atoms in the ferromagnetic Heusler alloys

The magnetic hyperfine fields,B _hf, for impurity¹¹⁹Sn atoms in Z sites of ferromagnetic Heusler alloys Co₂MnZ (Z=Si, Ge) are measured by the Mössbauer effect. At 77 KB _hf=–1.43±0.04 T in Co₂MnSi andB _hf=+1.05±0.05 T in Co₂MnGe. From the comparison between the values ofB _hf for Sn atoms in Co₂MnZ (Z=Si, Ge, Sn), it follows that the negative contribution toB _hf drops as the interatomic distance begins to increase. This radial dependence also manifests itself in the anomalies of the temperature dependences of the hyperfine fields. The temperature anomaly is positive for Sn in Co₂MnGe and negative for Sn in Co₂MnSi.     

Local magnetic properties of ultrathin ferromagnetic fcc-Fe-films on Cu(001)

Conversion electron Mössbayer spectroscopy (CEMS) on three monolayers (ML) thick metastable fcc-Fe(001) films grown epitaxially on a Cu(001) substrate under different conditions shows that these films are characterized by a distributionP(B _hf) of magnetic hyperfine fieldsB _hf. The vast majority of⁵⁷Fe nuclei experience relatively large hyperfine fields at low temperature. The temperature dependence of the most probable fieldB _peak was found to follow aT ^3/2 spin-wave law below 300 K. It is shown from the relative line intensities that preferential Fe spin orientation perpendicular to the film plane exists in films grown at 120 K, while preferential in-plane spin orientation is found for a growth temperature of 300 K. Coating a low-temperature grown Fe film by 2 ML of Cu(001) drastically reduces the hyperfine field, in contrast to the case of room-temperature grown Cu-coated films.Dedicated to Professor Ulrich Gonser on the occasion of his 70th birthday     

Kinetics of Atomic Cascade in Light Exotic Atoms

The magnetic hyperfine field B _hf for Cd in the Heusler alloy Pd₂MnSn at the site of chemically introduced Ag has been investigated by PAC following the ^– decay of ¹¹¹Ag. Sign and temperature dependence of B _hf have been determined. Comparison of the result B _hf(T=0)=+8.0(1) T with earlier data and ab-initio band structure calculations leads to the conclusion that the Ag activity has been incorporated at the Mn site.     

Hyperfine fields in the 5sp series studied by the low temperature nuclear orientation of83Rb,83Sr,85Sr and85Ym in iron

The hyperfine fields B_hf (RbFe), B_hf (SrFe) and B_hf (YFe) have been determined by the low temperature nuclear orientation of dilute samples of⁸³Rb,^83,85Sr and⁸⁵Y^m in an iron lattice to be B_hf (RbFe)=+54 (10) kG, B_hf (SrFe)=(?)100 (30) kG and B_hf (YFe)=?226 (10) kG. These results are compared with recent calculations for these fields (1), (2).     

Magnetic fields at 181Ta nuclei in Laves phases of RFe2 (R=Nd, Pr, Sm, Gd, Dy, Yb, Lu)

By studying the perturbed angular correlations of γ-rays emitted during the decay of ¹⁸¹Hf impurities in the Laves phases of PrFe₂, DyFe₂, and YbFe₂, we have investigated the magnetic hyperfine interaction between these compounds and its daughter nucleus ¹⁸¹Ta, and have determined the temperature dependence of the magnetic hyperfine fields. At room temperature we obtained the following values of these magnetic hyperfine fields B _hf:B _hf(PrFe₂)=7.6(1) T, B _hf(DyFe₂)=15.5(5) T, and B _hf(YbFe₂)=18.8(3) T. When taken together with data obtained previously, the results of our experiments show that for Ta nuclei in the RFe₂ Laves phases the values of B _hf depend strongly on whether R is a light or a heavy rare-earth element, which allows us to conclude that in these phases the value of the magnetic moment induced at the impurity Ta nuclei depends on the interatomic distance. Zh. éksp. Teor. Fiz. 111, 1085–1091 (March 1997)     

Nuclear orientation of82Br implanted into Fe

Nuclear orientation measurements are used to determine the hyperfine hamiltonian for⁸²Br implanted into Fe single crystals (dose 5×10¹⁴/cm^–2 implant energy 80 keV). Using a model based upon channeling measurements a good fit to the temperature-dependent gamma anisotropy is obtained for a pure magnetic interaction experienced by the 36±5% of Br which implants substitutionally of magnitudeB _hf (substitutional)=840±120 kG, withB _hf (non-substitutional)<150 kG. This hamiltonian is used to deduce unknown multipole mixing ratios in the daughter⁸²Kr decay. Hyperfine field systematics are shown to indicate a substitutionalFeBr field of 1000 kG, and the origins of this field and the smaller interstitial interaction are discussed.     

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.     

Magnetism of ultrathin Fe(110) films

Application of conversion electron Mössbauer spectroscopy (CEMS) to structural and magnetic analysis of ultrathin films and their interfaces is reviewed. Fe(110) films were prepared on W(110) under UHV conditions and analyzed in situ. CEMS provides detailed information on the mode of growth and film structure and on magnetic hyperfine fields, B _hf. Local structure of B _hf across the film is discussed in relation to modifications of magnetic order caused by the finite (including monolayer) film thickness and by the electronic structure of the interface.     

Magnetic Moment of the 3/2− Ground State of 185W

Nuclear magnetic resonance measurement have been performed for ¹⁸⁵W oriented at 8 mK in an Fe host. The magnetic hyperfine splitting frequency at an external magnetic field of 0.1 T was determined to be 196.6(2) MHz. With the known hyperfine field of B _hf = −71.4(18) T, the nuclear magnetic moment of ¹⁸⁵W is deduced as μ(¹⁸⁵W) = +0.543(14) μ_N.     

Study of magnetic behaviour of CeRh3B2 using111Cd probe

Using¹¹¹Cd probe nuclei, the transferredH _hf(T) is measured down to 35 K in CeRh₃B₂ using TDPAC technique. The angle β between the EFG and the direction of magnetization is obtained to be 90°. The observed smallH _hf(T) may be a consequence of the reduced moment on Ce in CeRh₃B₂.     

Antiferromagnetic spin correlations in palladium-based Pd-Fe, Pd-Fe-Ag, and Pd-Fe-Rh magnetic alloys

The magnetic structure of Pd_1?x Fe_x (x=0.03, 0.06, 0.10, 0.15, and 0.20) alloys is investigated using the method of ⁵⁷Fe-Mössbauer spectroscopy. The distribution functions P(B _hf) of hyperfine magnetic fields have a discrete structure defined by variations of the contribution to B _hf from the magnetic moment of the neighboring Fe atoms. The anomalies of intensities of components of the functions P(B _hf), which increase with the concentration of iron, are indicative of the instability of configurations with a large total spin and of the formation of local spin configurations with the antiferromagnetic orientation of magnetic moments. The probability of formation of such configurations is defined by the competition of the ferromagnetic Fe-Pd exchange interaction with the direct antiferromagnetic exchange between the nearest neighboring atoms of Fe. An Ag or Rh impurity effectively induces the process of spin flipping, which explains the anomalously strong effect of impurities on the magnetic ordering temperature. The results confirm the presence in Pd-Fe alloys of perturbations of long-range ferromagnetic order revealed by neutron diffraction.     

The magnetic hyperfine field of bromine in iron by NMR/ON

Nuclear magnetic resonance of⁸²Br oriented at low temperature in iron has been observed with a sample prepared by ion implantation atT<0.2 K. The asymmetric resonance signal can be decomposed in a broad background signal and a narrow line of FWHM=1.8 (4) MHz which can be attributed to⁸²Br in undisturbed substitutional sites of Fe. From the center frequency of this narrow line (B _ext=0)=201.86(13) MHz we derive the magnetic hyperfine field asB _hf(BrFe)=81.38(6) T. This value is considerably larger than the result of theoretical calculations.