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Thin films of magnetite (Fe3O4) with thicknesses in the range 10–1000 nm have been produced by the XeCl excimer laser (λ = 308 nm) ablation of both Fe3O4 and metallic 57Fe targets. Deposition conditions have been investigated in an attempt to fabricate films reproducibly at low laser fluences so as to minimize ablation bouldering. The ablation of metallic Fe has been shown to produce a smaller concentration of boulders than the ablation of bulk magnetite. It is believed that this is mainly due to the difference in primary ablation mechanisms between the two target materials. The use of single-crystal, lattice-matching substrates was found to be necessary at lower fluences (1–3 J cm−2) for the ablation of metallic Fe, whereas polycrystalline, non-lattice-matching substrates were adequate for deposition with moderate laser fluences (5–6 J cm−2). Film quality has been assessed by a range of techniques including XRD, SEM, AFM/MFM and CEMS. Using CEMS it has been established that the films produced from a metallic target contained a significant amount of metallic Fe, together with secondary oxide phases. The influence of film thickness on the Verwey transition has been investigated via electrical conductivity and SQUID magnetometry. It is found that there is a systematic reduction of Verwey temperature with decreasing film thickness; this is attributed to the effect of strain.

The temperature dependencies of the Mossbauer parameters for 57Fe-doped YBa2Cu3Oy (y ≈ 6.80, Tc ≈ 80 K) reveal anomalies near 90, 170, 230 and 280 K. These anomalies were confirmed with X-ray diffraction and heat capacity measurements using the same samples. The thermal history of the sample was found to influence the superconducting characteristics and the temperature behavior of the Mossbauer effect probability and linewidth. The results are discussed on the basis of the calculated low temperature phase diagram and possible ferro- and antiferroelectric phase transitions.

The magnetic hyperfine fieldsBhf near the interface in epitaxial Fe(100)/Pd thin film structures were analyzed using in-situ57Fe conversion electron Mossbauer spectroscopy.Bhf is enhanced by about 12% in the 2nd Fe monolayer and approaches the Fe bulk value after a few oscillations within 8–10 Fe monolayers. This oscillating behavior can be described by a superposition of an exponential short-range and an RKKY-like long-range exchange interaction.

The applicability of a low-noise scintillation detector (ScD) for the registration of electrons of several keV energy has been studied employing photomultipliers (PM) of different types and sizes. With the application of a sedimented P-47 scintillation screen, the values of the low-energy sensitivity limit and those of the light conversion coefficient were determined as about 2.7–4.7 keV and 2.8–6.6 photoelectrons/keV, respectively, for the set of PM's (Philips-Valvo XP 2020, Philips-Valvo XP 2052, Philips-Valvo XP 2972, EMI 9124a) studied. It is concluded that such scintillation detectors might be used advantageously as electron counters in the range of E > 5 keV. Applications below this kinetic energy value are also feasible when applying a floating acceleration of several kV to the ScD — a voltage much lower than the values required for Everhart-Thornley detectors.

In Y/Fe/Y layered structures the Fe interlayer grows in an amorphous structure up to a critical thickness of d Fe = 2.3 nm. Above this thickness the Fe film transforms to a nanocrystalline structure. The magnetic properties of the amorphous Fe film (a-Fe) were determined by means of 57 Fe conversion electron Mossbauer spectroscopy and magnetization measurements. The average magnetic moment of a-Fe amounts to if μ = (1.2±0.2)μ B and the ferromagnetic Curie temperature to T c = (80±3) K. There seems to be a broad distribution of the magnitude of the magnetic moments. No indication of spin glass properties was found.

197 Au-Mossbauer results are reported for a series of alkali metal gold chalcogenides: Na 3 AuS 2 , KAuS, CsAuS, K 4 Au 6 S 5 , KAuSe, NaAuTe, KAuTe, RbAuTe and CsAuTe. Isomeric shifts (ISs) and quadrupole splittings (QSs) correspond to the region expected for gold atoms of oxidation state + 1 in the QSIS correlation diagram. The compounds with linearly coordinated gold atoms exibit a marked linear relationship between IS and QS. The highest values of QS and IS are found for Na 3 AuS 2 . Progressively lower values are manifested as the chalcogen atom is changed from sulphur to selenium to tellurium or when the alkali metal is exchanged for a less electronegative element respectively. Correspondingly the parameters of alkali metal gold chalcogenides with a smaller content of alkali metal are smaller. The Mossbauer spectra of the ternary tellurides show the expected difference between the threefold-coordinated gold atoms of the layer structures and the twofold-coordinated gold atoms of the chain structures. Eventual AuAu interactions could not be proved by these Mossbauer measurements. The short AuAu distances, detected by X-ray analysis, are possibly van der Waals contacts.

The 119 Sn Mossbauer effect technique (300-4.2 K) has been used to study the local magnetic order in La 2− x Sr x (Cu 0.995 Sn 0.005 )O 4+δ for three different Sr concentrations corresponding to the antiferromagnetic state ( x = 0), the spin-glass-like state ( x = .04), and the superconducting state ( x = 0.15). Contrary to previous reports we observe no transferred hyperfine (hf) field at the Sn nuclei in the superconducting state down to 1.7 K. On the other hand, we observe small transferred hf fields in both the antiferromagnetic ( x = 0) and the spin-glass-like state ( x = 0.04). In the spin-glass-like sample ( x = 0.04) we find in the temperature range 10 K ⩽ T ⩽ 200 K a significant increase of the Mossbauer linewidth and an anomalous change of the quadrupole splitting which we attribute to a short range structural disorder as recently reported by perturbed angular correlation measurements of 111 In on La 2− x Sr x CuO 4 (0 ⩽ x ⩽ 0.07). The magnetic behaviour of this sample ( x = 0.04) has been further investigated by 139 La-NQR measurements at low temperatures (1.5 K ⩽ T ⩽ 12 K). Here, we observe an enhancement of the relaxation rate (1/ T 2 ) below about 7 K.

The magnetic hyperfine fields near the interfaces in Fe/M (M = Cr, Gd, Y) layered structures were analyzed with monolayer resolution by means of 57 Fe conversion electron Mossbauer spectroscopy (CEMS). It was found that the range of magnetic FeCr interaction extends only up to the second Fe neighbor at the Fe/Cr interface. In contrast, at the Fe/Gd interface the interaction range is four times larger. This is explained by a polarization of the Fe conduction electrons by the large Gd 4f moment. By inserting a spacer layer of Y between the Fe and Gd films an oscillating modification of the Fe hyperfine field was observed in dependence of the Y layer thickness.

Results of CEMS measurements performed in vacuum applying a channeltron and a low-noise thin-layer scintillation detector equipped with different types of thin-layer scintillators (e.g. P-47 CsI(Tl) of different thickness) are reported here. The experimental merits of different detectors for different Miossbauer isotopes of samples are evaluated.

Increasing attention is being paid to non-conventional Mossbauer methods in view of the extension of Mossbauer Spectroscopy (MS) to a broadening field of applications. With such long-lasting experiments the shortening of the measuring time required for a given statistical significance is of major practical importance. It is shown that the statistical utility rateu allows one to determine which experimental parameters have a primary role, and it also enables sucessive optimization. It is pointed out for various MS measurements that the strategy for improving the experimental performance is strongly dependent on the given problem. As examples, time-differential Mossbauer measurements and conversion electron Mossbauer spectroscopy are discussed.

The intermetallic alloy EuPdAs exhibits a first order phase transition at 180 K. The transition is seen by anomalies in lattice parameters, susceptibility, resistivity, Moessbauer effect and X-ray absorption. It is accompanied by an increase of the Eu valence from 2.15 to 2.40 between 300 K and 4 K. The nature of the non-integral valence and the phase transition are discussed.

The interface properties are crucial for most of the unique properties of ferromagnetic multilayers. Typical examples and results of the influence of interface structural and electronic properties on the magnetic anisotropy and the interlayer exchange coupling effects will be reviewed for various Fe/M interfaces (M: Cr, Al, Ag, Au, Gd, Y). Emphasis will be put on interface investigations by 57Fe-Conversion Electron Mossbauer Spectroscopy (CEMS) on magnetic interactions at Fe/Gd interfaces and on the recent studies of amorphous Fe films. Those films can be stabilized below a critical thinkness of about 2.3 nm at Fe/R interfaces (R: Gd, Y). Between Y layers amorphous Fe can be studied to temperatures well above the average Curie temperature of Tc = 80 K.

The assignment of the four57Fe Mossbauer sites which are observed in Fe-substituted YBa2Cu3Oy is presented. We present a systematic study of highly-controlled samples with low Fe-concentration over the whole oxygen concentration range. Two sites are found to dominate in the limit of high oxidation (y→7), indentified as Fe4+ on the two crystallographic Cu sites: Cu(1) and Cu(2). These are replaced at lower oxidation (y→6) by two others, which we identify with Fe3+ on these same two sites. Consistency is found with the sign of the electric field gradient (EFG), the asymmetry parameter η and the isomer shiftI S for this model. The magnetic structure in the limit y→6 shows changes in the antiferromagnetic (AF) structure dependent on iron concentration. Mossbauer and spin-echo NMR results show a change in the Cu(2) AF layer sequence at low temperatures, without any magnetic moments on the Cu(1) chain sites.

Recently we have studies β-Al9Si(Mn1−x Fe x )3 using Mossbauer effect spectroscopy withx=0.28 and discovered a new transition at about 80 K. Neutron diffraction studies down to low temperatures reveal no structural changes, so that this transition at 80 K is indeed of magnetic origin. The magnetic susceptibility shows a small maximum near this temperature superimposed on a large Curie-like background. In addition to this transition, the Curie-like background shows a cusp near 4 K. We thus infer a magnetic double transition in this disordered alloy. These magnetic transitions have been followed to lower Fe concentrations (x=0.10 and 0.20) by both Mossbauer spectroscopy (T c ) and by magnetic susceptibility (T g). It is found thatT C decreases rapidly with decreasing Fe concentration, whileT g remains relatively constant. The saturation hyperfine fieldB hf(0) decreases rapidly with decreasingx, indicating that the Fe atoms loose their magnetic moments in the limit of infinite dilution, and the important role played by Fe−Fe nearest neighbors in determining the magnetic properties.

The valence of Bi and its substituents Sn and Sb are investigated in the high temperature superconductor (Bi0.8X0.15Sb0.05)2Sr2Ca2Cu3Oy (often denoted 2223) where X=Pb or Sn. Pb and Sn are isoelectronic with the valence states 2+ and 4+; Bi and Sb are as well with valence states 3+ and 5+. The valence state of Sn and Sb has been obtained from Mossbauer spectroscopy: they exist in the high charge states 4+ and 5+ respectively. Sn, Sb, and presumably Pb, take on the high valence state, and so furnish electrons to the conduction band. This is probably the reason why, although the (Pb, Sb)-doping aids in stabilizing the 2223 crystal structure, it is detremental to the electronic properties which lead to the superconducting phase. The valence state of Bi has been studied using X-ray photoelectron spectroscopy (XPS). These results show clearly that the Bi-based superconductor has a metal-like density of states at the Fermi level, and that the valence in the (Pb, Sb)-doped compounds is less than 3. This very surprising change in valence will have a profound effect on the superconducting properties, and is probably associated with the high valent states of Pb, Sn and Sb.

Integral Conversion Electron Mossbauer Spectroscopy (ICEMS) when aimed at the study of clean surfaces in UHV often leads to unfavourable measuring geometry and consequently to long recording times. Possible means of shortening of the measuring times are analyzed. It is shown that criteria for experimental preferences may be distinctly different for different sample structures and for different kinds of electron detectors.

As depth-selective conversion electron Mossbauer-effect measurements present a difficult task in Mossbauer spectroscopy due to the long recording times involved, the shortening of the measuring times is of major practical importance. Possible improvements of the overall experimental performance and measuring time gains due to efficiency increase and back-ground reduction will be analyzed; advantages of a scintillation counter over a channeltron for57Fe DCEMS applications will be discussed.

The magnetic hyperfine (hf.) fields at the Fe/Cr interface were analyzed in epitaxial Fe/Cr thin film structures of (100)- and (110)-orientation with monolayer resolution by means of in-situ57Fe Conversion Electron Mossbauer Spectroscopy (CEMS). The hf. field (300 K) in the 1st Fe-monolayer (ML) at the interface has been found to be strongly reduced to 22.0/20.9 T for (110)-/(100)-orientation, whereas the 2nd and 3rd ML reveal a slightly increased hf. field of 33.7 T as compared with the Fe-bulk value of 33.4 T. The temperature dependence of the hf. field at the interface shows aT 3/2 spin wave law. The spin wave parameters are enlarged with respect to the bulk value indicating a reduced exchange interaction. A discontinuity in theT 3/2-dependence is interpreted by the onset of magnetic order (Neel-temperature) of the Cr layers adjoining the57Fe probe layer.

Recently we have studies β-Al9Si(Mn1−xFex)3 using Mossbauer effect spectroscopy withx=0.28 and discovered a new transition at about 80 K. Neutron diffraction studies down to low temperatures reveal no structural changes, so that this transition at 80 K is indeed of magnetic origin. The magnetic susceptibility shows a small maximum near this temperature superimposed on a large Curie-like background. In addition to this transition, the Curie-like background shows a cusp near 4 K. We thus infer a magnetic double transition in this disordered alloy. These magnetic transitions have been followed to lower Fe concentrations (x=0.10 and 0.20) by both Mossbauer spectroscopy (Tc) and by magnetic susceptibility (Tg). It is found thatTC decreases rapidly with decreasing Fe concentration, whileTg remains relatively constant. The saturation hyperfine fieldBhf(0) decreases rapidly with decreasingx, indicating that the Fe atoms loose their magnetic moments in the limit of infinite dilution, and the important role played by Fe−Fe nearest neighbors in determining the magnetic properties.

Magnetic hyperfine (hf) fields near the Fe/Cr-interface in epitaxial thin film structures with (110)- and (100)-orientation were analyzed by means of in situ conversion electron Mossbauer spectroscopy (CEMS). The hf field at room temperature in the first Fe-monolayer (ML) at the interface is strongly reduced to 22.0 T (110) and 20.9 T (100) compared with the Fe-bulk value of 33.4 T. In contrast, in the second and third Fe-monolayer with respect to the interface the hf field was enhanced by 0.3 T to 33.7 for both film orientations.

Barium hexaferrite particles prepared by sol-gel technique yield best magnetic characteristics if a large barium surplus is used. Therefore, the powder sample has to be etched after the annealing process in order to get samples without intermediate phases. The used temperatures below 900°C and times shorter than 1h cause nanocrystalline hexaferrite particles with a specific saturation magnetization above 700 Acm 2 /g and a coercivity up to 470 kA/m.

The magnetic properties of bulk metals, for instance, their magnetic moments and anisotropies, have been extensively studied in the past and are now well understood in great detail for most homogeneous metals and alloys. In contrast, the magnetic properties of ultrathin film interfaces and surfaces, which usually differ from the bulk properties, have generated growing new interest over the last decade. This rapid growth in interest has resulted because the preparation of thin films with well defined compositions and structures, by molecular beam epitaxy in an ultra high vacuum or by sputtering techniques, has shown enormous progress over the past few years. As a result it has even been possible to prepare thin films of materials with crystal structures deviating from the usual crystal structure of the bulk material. Examples are thin films of fcc-iron or bcc-cobalt. Simultaneously with the growth in preparative methods, many subtle new experimental methods for the analysis of the various properties of thin films and interfaces have been developed. In addition, modern band structure calculations have provided a new and powerful tool for the theoretical treatment of the magnetic properties of thin films and interfaces.

The exchange biasing field (Heb) and coercive field (Hc) of molecular-beam-epitaxy (MBE) grown Cu/Ni80Fe20/Fe50Mn50 samples in [111], [001] and [110] orientations were investigated by Kerr effect measurements. A strong dependence of Heb and Hc on the growth orientation is observed. A strong uniaxial in-plane anisotropy introduced by the Fe50Mn50 layer was found for the [110]-oriented sample. Conversion electron Mossbauer studies revealed a roughness of 2–3 A and no significant moment reduction at the Ni80Fe20/Fe50Mn50 interface.

The growth of Gd/Fe layered structures prepared by evaporation in UHV was studied by means of in situ $^{57}\mathrm{Fe}$ conversion-electron M\"ossbauer spectroscopy and cross-section high-resolution transmission electron microscopy. The Fe layer grows on the Gd sublayer in an amorphous structure up to a critical Fe thickness of ${\mathit{d}}_{\mathit{c}}$=2.3\ensuremath{\mp}0.1 nm. On further increasing the Fe thickness, a rapid transformation to nanocrystalline structure throughout the total Fe layer occurs. This effect is suggested to be due mainly to the extreme misfit between the structural parameters of Fe and Gd.

The temperature dependence of the magnetic hyperfine (hf.) fields near the interfaces in epitaxial Fe/Cr and partly epitaxial Fe/Gd bilayers were measured using 57Fe Conversion Electron Mössbauer Spectroscopy (CEMS). It was found that the Fe-Cr magnetic interaction extends only up to the second Fe-neighbor at the Fe/Cr interface, whereas the interaction range at the Fe/Gd interface is four times larger. For comparison the hf. fields and magnetic moments for Fe/Cr multilayers were obtained performing LMTO (Linear Muffin Tin Orbital) band structure calculations. The Néel temperature of a thin Cr-interlayer in a Fe/Cr/Fe sandwich structure was determined in dependence of the Cr-layer thickness.