Program: K2 Magnetism K2 Magnetism K2.1. J.-M. Greneche (Le Mans): Magnetic Iron-based Oxides Investigated by 57Fe Mössbauer Spectrometry K2.2. V. M. Nadutov (Kiev): Hyperfine Magnetic Structure and Magnetic Properties of Invar Fe-Ni-C Alloys K2.3. K. Závěta (Prague): Magnetic Multilayers and Mössbauer Spectroscopy: Case History of Fe/FeSi K2.4. E. Voronina (Izhevsk): Mattis' Magnetic and Disordered Systems: Theoretical Prediction, Experimental Detection, Local Atomic and Magnetic Structure, Temperature Behaviour O2.1. A. Lancok (Prague): Magnetic Moment of Iron Nitrides: Mössbauer Spectroscopy versus Magnetic Measurements K2.1 Magnetic Iron-based Oxides Investigated by 57Fe Mössbauer Spectrometry J.-M. Greneche Laboratoire de Physique de l'Etat Condensé, UMR CNRS 6087, Université du Maine, Le Mans, France The physical properties of the iron-based oxides, as ferrites, garnets, manganites, double perovskites, were widely investigated during recent years because of their fundamental aspects and their technological interests. Among the more relevant information, which are basically required, one should mention the estimate of the tetrahedral and octahedral iron content, the magnetic configuration and the electronic configuration. Since zero-field Mössbauer spectra might exhibit rather complex hyperfine structures with a strong lack of resolution preventing an accurate estimation of hyperfine parameters, in-field Mössbauer spectra provide more relevant and clear information. In addition, the relaxation superparamagnetic phenomena can be investigated in the case of nanoparticles and nanostructured powders. We report various examples to illustrate how in-field Mössbauer spectrometry is a suitable tool for investigating such systems. K2.2 Hyperfine Magnetic Structure and Magnetic Properties of Invar Fe-Ni-C Alloys V.M. Nadutov, Ye.O. Svystunov, T.V. Yefimova and A. Gorbatov G.V. Kurdyumov Institute for Metal Physics of the N.A.S. of Ukraine, Kyiv, Ukraine The data on magnetic structure and magnetic properties of the fcc. Fe-Ni-based alloys are important to expand knowledge on invar problem in the Fe-36%Ni alloy. In order to influence on atomic order and magnetic structure of the alloy we changed the base Fe-36%Ni composition decreasing the Ni concentration to 30% and additionally alloying with carbon. The binary fcc. Fe-Ni alloys and carbon-containing Fe-Ni-C alloys were studied by means of Mössbauer spectroscopy and magnetic methods. The saturation magnetization and magnetic susceptibility was measured in the alloys within the temperature range 80 ¸ 300 K. The martensitic, Ms and Curie, Tc temperatures were estimated from the temperature dependences. An essential shift of the points and expansion of the magnetic gamma-phase range under alloying with carbon in comparison with binary Fe-Ni alloy was revealed. In order to characterize behaviour of the curves the transmission Mössbauer spectra of the Fe-Ni-C alloy were obtained at room temperature. The shape of the spectra was considerably changed with increasing annealing temperature and carbon concentration. The densities of the hyperfine magnetic fields distribution were obtained using the Window method added by the procedure of fitting the isomeric shifts. The considerable effect of carbon on the hyperfine magnetic structure was observed. The narrow low field peak and broadened high field range was revealed on the P(H) curve related to the Fe-Ni-C alloy. This work was supported by the Science and Technology Centre in Ukraine (the project #2412). K2.3 Magnetic Multilayers and Mössbauer Spectroscopy: Case History of Fe/FeSi K. Závěta Institute of Physics, Academy of Sciences of the Czech Republic and Joint Laboratory of Mössbauer Spectroscopy Praha, Czech Republic On the canonical example of Fe/Cr/Fe sandwiches it was shown that the varying thickness of the spacer leads to the damped oscillations of the intensity of interaction between the ferromagnetic layers. As a result the orientation of their moments corresponding to the minimum energy may be parallel, antiparallel, perpendicular or canted. The antiparallel or generally non-parallel mutual orientation is particularly attractive due to the application potential of the Giant Magnetoresistance effect. The spacers used may be conducting or even insulating/semiconducting, strongly or weakly magnetic. For the properties of the layers the quality of the interface strongly depending on the technological conditions of their preparation is also a serious factor. The multilayers with Fe as the ferromagnetic layer and FeSi as the spacers display some peculiar magnetic properties indicating the presence of both bilinear and biquadratic terms in the interaction energy. Because of the presence of Fe in both components, they are a very suitable object for the study by means of Mössbauer Spectroscopy (MS). The problems, that were addressed and at least partly answered by this method, comprise among others the orientation of magnetic moments of the layers under various circumstances both in the normal and in-plane directions and the sharpness of the interface, i.e., the interdiffusion between the layer and spacer. Some non-trivial methods were used for solving these questions including the synchrotron radiation MS, conversion electrons MS, and the use of 57Fe-enriched iron at specific positions. K2.4 Mattis' Magnetic and Disordered Systems: Theoretical Prediction, Experimental Detection, Local Atomic and Magnetic Structure, Temperature Behaviour E.V. Voronina1, E.P. Yelsukov1, A.V. Korolyov2 and S.K. Gdovikov3 1) Physical-Technical Institute UrD RAS, Izhevsk, Russia 2) Institute of Metal Physics UrD RAS, Ekaterinburg, Russia 3) Institute of Nuclear Physics, Moscow State University, Moscow, Russia For the systems with atomic and spin disorder Mattis [1] proposed the model in which spin-spin interactions were random in sign but did not result in frustrations. This model describes the spin structure with the magnetic moments directed opposite to each other, randomly distributed over the lattice sites and m = 0. Besides, from theoretical calculations [2] for non-ordered Fe alloys with metalloids it followed that the magnetic moment of the Fe atom with a certain number of metalloid atoms in the nearest neighbourhood could orient in the direction oppositely to local magnetization. Later in [3] it was shown that in such a non-ordered system the temperature dynamics of the magnetic moments directed along and conversely the magnetization was different. The non-ordered systems of Fe with metalloids (Al, Sn) seemed the very ones, for which all above theoretical considerations would be valid. Taking them into account we have analysed the results of temperature (5-450K) Mössbauer spectroscopy and magnetic studies in external magnetic fields up to 5T of the non-ordered Fe100-xSnx (x = 46-62 at.%) and Fe100-xAlx (x = 35-60 at.%) alloys. On this basis the following models of local magnetic arrangement were suggested: the magnetic moment of Fe atom with 7 and more Al or 9 and more Sn nearest neighbours aligns itself oppositely to the magnetization and all moments are arranged chaotically. Thus, Fe alloys with x > 45 at. % Al, Sn can be specified as Mattis' magnetics. The peculiar temperature dependence of the reduced hyperfine magnetic field, the increase of the non-magnetic component in Mössbauer spectrum starting at the temperature long before the magnetic ordering temperature, the maxima on the temperature dependence of magnetization in the low external field can be explained by short-wave spin excitations (SWSE). Mössbauer spectra in the applied magnetic field confirm that SWSE should be higher for the local magnetic moments of configurations with many metalloid nearest neighbours. The evolution diagram of the magnetic arrangement versus the temperature is constructed. [1] D.C. Mattis, Phys.Letters 55A (1976) 421. [2] A.K. Arzhnikov, L.V. Dobysheva, J.Magn.Magn.Mater. 117 (1992) 87. [3] A.K. Arzhnikov, L.V. Dobysheva, Phys.Lett. A195 (1994) 176. O2.1 Magnetic Moment of Iron Nitrides: Mössbauer Spectroscopy versus Magnetic Measurements A. Lancok1,2 and K. Závěta1 1) Joint Laboratory for Mössbauer Spectroscopy, MFF UK, Prague, Czech Republic 2) Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, Rez, Czech Republic Iron nitride powders were prepared by nitriding iron particles in a mixture of H2 and NH3 at 750 oC and rapid quenching. The mixture of austenite and martensite formed was further milled in NH3 gas and subsequently tempered at 130 °C. The materials were characterized by chemical analysis, XRD and neutronography. Their magnetic moments were measured in a SQUID magnetometer at 10 and 300 K and compared with the local Fe moments for various sites of the present phases, including the desired alpha'' Fe16N2 and a defect phase. The local moments were evaluated from the hyperfine fields from Mössbauer spectra obtained from powdered samples at 300, 78 and 10 K.