Mössbauer spectroscopy is a powerful and well established method for wide variety areas of researches, such as physical-, chemical-, biological-, and earth-sciences. One of the most outstanding features of this method is that element specific measurement is possible. Particularly, by using synchrotron radiation, we can measure Mössbauer effect without preparing radioactive Mössbauer sources and, therefore, element specific measurement is attained. Moreover, the use of synchrotron radiation allows us to measure element- and site-specific phonon density of states. In this article, the concept of the Mössbauer spectroscopy using synchrotron radiation and nuclear resonant inelastic scattering spectroscopy is reviewed. In particular, a new method that gives absorption Mössbauer spectra using synchrotron radiation and is applicable for almost all the Mössbauer nuclides is introduced. The features of these methods for the study of condensed matter science including surface science are discussed.
In-beam Mössbauer spectroscopy using an unstable nuclear probe or an energetic radioactive isotope (RI) beam is one of the most powerful technique that is used to observe the site occupations, dynamic atomic jump processes, and exotic chemical states of extremely diluted atoms in a material. The on-line Mössbauer technique offers unique information of the probe atoms under non-equilibrium or metastable conditions in the Mössbauer lifetime. Here, the outlines of recent results of 57Mn implantation experiment and the facility of RIKEN RI-beam Factory are explained.
In the case of mixed-valence system whose spin states are situated in the spin crossover region, new types of conjugated phenomena coupled with spin and charge are expected. From this viewpoint, we have investigated the multifunctional properties coupled with spin, charge and photon for the organic-inorganic hybrid system, A[FeIIFeIII(dto)3] (A = (n-CnH2n+1)4N, spiropyran; dto = C2O2S2) by means of the magnetic susceptibility and 57Fe Mössbauer spectroscopy. In (n-CnH2n+1)4N[FeIIFeIII(dto)3], in addition to the ferromagnetic transition, a new type of phase transition called charge transfer phase transition (CTPT) takes place around 120 K, where the thermally induced charge transfer between FeII and FeIII occurs reversibly. The charge transfer phase transition and the ferromagnetic transition for (n-CnH2n+1)4N[FeIIFeIII(dto)3] remarkably depend on the size of intercalated cation. In the case of (SP) [FeIIFeIII(dto)3] (SP = spiropyran), the photoinduced isomerization of SP under UV irradiation induces the charge transfer phase transition in the [FeIIFeIII(dto)3] layer and the remarkable change of the ferromagnetic transition temperature.
Nuclear resonant inelastic scattering (NRIS) is a unique tool to investigate element-specific phonon density of states by Mössbauer nuclei. This technique enables us to investigate the dynamics of the specific atoms which contain Mössbauer nuclei. For recent times, much attention to the potential of thermoelectricity has been paid in cage-structured compounds such as filled skutterudites, clathrates and so on. Since the proposal of “phonon-glass-electron-crystal” model, thermal insulation due to phonons has been expected as one of the important parameters in their thermoelectricity. We applied NRIS using several nuclei to the series of cage-structured compounds. We mainly show the recent results of filled skutterudites here.
Mössbauer spectroscopy is a powerful experimental tool for the investigations on local electronic and vibrational properties of solids. On the other hand, the recently developing field of “spintronics”, where spins of conduction electrons play a key role for transport phenomena, is requiring to control the size and physical properties of materials in nanoscales. Using Mössbauer spectroscopy it becomes possible to investigate local magnetism and electron-spin polarization of materials, which can be important information for further development of spintronics. In this article, Mössbauer spectroscopic studies on spintronics-related materials in the early stage after the discovery of giant magnetoresistance effect are outlined briefly, and then recent studies on Heusler-alloy-based layered structures are introduced topically.
A “Mössbauer spectroscopic microscope” is presented in this review article. The microscope uses a Multi-Capillary-X-ray (MCX) lens to focus 14.4 keV-γ-rays. It is operating in a laboratory combined with a field emission type scanning electron microscope (FE-SEM). This microscope yields a two-dimensional mapping image of 57Fe probes with a space resolution of about 50 μm in comparison with the microstructure observed by FE-SEM. The detection limit for 57Fe atoms appears to be less than 101657Fe/cm3 in Si matrix. We detect “57Fe Mössbauer effect” either by 14.4 keV-γ-rays or characteristic X-rays of Fe on Si-PIN detector or by conversion electrons and Auger electrons on micro-channel plate (MCP) as function of the focused γ-ray positions. Two examples of the applications of this microscope are shown: one for SUS304 steel which contains Austenite and Martensite phases, and the other for 57Fe contaminated multi-crystalline Si which is used for solar cells.