M. Kopcewicz

A direct determination of the quadrupole splitting in ferromagnetic amorphous metals

Abstract We introduce a new method for direct determination of the quadrupole splitting of amorphous alloys in the ferromagnetic state. The radio frequency induced collapse of the magnetic hyperfine structure leaves pure quadrapole split Mossbauer spectra. This allows the direct evaluation of the distribution of quadrupole splittings and isomer shift.

Short range order in metallic glasses from quadrupole splitting distributions

Changes are observed in the short range order of several Fe based amorphous alloy systems through the quadrupole splitting distributions. The quadrupole splittings are determined directly in the ferromagnetic state by using the radio frequency collapse of the magnetic splitting.

Quadrupole splitting distributions of amorphous transition metal-metalloid alloys

The technique of radio-frequency collapse is used to determine the quadrupole splitting distributions of ferromagnetic amorphous alloys, FexNi75-xSi10B15 and FexSi90-xB10. In both cases the concentration dependence of the average quadrupole splitting QS, determined by Mossbauer spectroscopy, suggests a change in short-range order as predicted by structural models.

Radio Frequency Field-Induced Effects in Ferromagnetic Materials

The possibility of influencing the Mossbauer effect with an external radio frequency (rf) field was recognized in the early years of the “Mossbauer era.” It was found that the high-frequency piezoelectric vibration of a Mossbauer single-line source, induced by a quartz transducer, results in a modulation of the Mossbauer γ-radiation that may be observed as sidebands in the spectra.1 In this experiment, the source as a whole was vibrated mechanically. However, when the rf magnetic field is applied to a ferromagnetic magnetostrictive material, each atom is forced to vibrate with the external field frequency and the spectrum then consists of the original carrier hyperfine split pattern and the infinite set of satellite lines formed at the positions determined by the rf field frequency. These satellite lines, called the rf sidebands, were first observed for metallic iron.2–5 Soon a new effect was discovered, the so-called rf collapse effect.5,6 It occurs when the magnetic rf field forces the fast reversal of the sample magnetization. This results in the oscillation of the magnetic hyperfine field at the iron nuclei in response to the applied rf field. When the frequency of the rf field is larger than the Larmor precession frequency, the magnetic hyperfine field averages to zero, and in the Mossbauer spectrum a collapse of the entire Zeeman pattern to a single line or a quadrupole doublet is observed. This effect was studied for various soft ferromagnetic alloys and ferrites.5–11

Mössbauer study of the separation of the rf sideband and collapse effects in invar

Abstract This report describes an investigation of the influence of coating of invar foil with various materials on the sideband and collapse effects caused by an applied r.f. magnetic field. It is shown that coating of invar foil with nonmetallic materials causes a decrease of the r.f. sideband effect without affecting the r.f. collapse effect. Coating with metallic materials reduces both r.f. effects because of screening due to the r.f. field. The separation of the r.f. sideband and collapse effects due to coating allows us to distinguish the different origins of these effects, and suggests that the r.f. sidebands are of magneto-acoustic origin, while the r.f. collapse is of purely magnetic origin.

Mössbauer study of the magnetic properties of nanocrystalline Fe80.5Nb7B12.5 alloy

The nanocrystalline body-centered-cubic (bcc)-Fe phase was formed by controlled 1 h annealing of the amorphous Fe80.5Nb7B12.5 alloy at temperatures ranging from 490 to 650 °C. The microstructure and magnetic properties of the nanocrystalline alloy were investigated by Mossbauer spectroscopy, differential scanning calorimetry, and quasistatic hysteresis loop measurements. Conventional Mossbauer spectroscopy allowed identification of phases and the determination of their relative content. The specialized radio frequency (rf)-Mossbauer technique, which employs the effects induced by the rf magnetic field (rf collapse and rf sideband effects) allowed us to distinguish the magnetically soft amorphous and nanocrystalline phase from the magnetically harder microcrystalline Fe. The rf-Mossbauer experiments performed as a function of the rf field intensity allowed determination of the anisotropy fields in each phase of the nanocrystalline alloy (amorphous matrix, nanoscale bcc-Fe grains). The measurements of the h...

Mssbauer study of iron-containing atmospheric aerosols

The Mössbauer technique was applied to study the seasonal variations of iron concentration in atmospheric air. The concentration of iron in air was calculated by the “area method” from the experimental spectra obtained. From the shapes of the Mössbauer spectra it was concluded that iron appears as Fe2O3 in the form of ultrafine particles in the superparamagnetic state. The measurements as a function of temperature [from 300 to 75 K) made it possible to estimate the size of iron-containing aerosol particles. Correlation of the seasonal variations of iron concentration with meteorite activity was discussed. This method was applied also in investigations of iron concentration variations with air radioactivity due to nuclear explosions performed in the atmosphere. Attempts were made to find a relation between air pollution and the concentration of iron in the air.

Proton irradiation and solid state reaction of Fe−Zr multilayers

The amorphization of Fe−Zr multilayers due to ion-beam mixing and solid state reaction is studied in detail using the CEMS and CXMS. The nature of the amorphous Fe−Zr phase produced by both processes is the same suggesting that diffusion of Fe is an important mechanism during ion-beam mixing.

Mössbauer study of r.f. collapse in permalloy

Abstract The fast relaxation of hyperfine magnetic field forced by external r.f. field was studied for permalloy foils. The application of r.f. field caused a complete collapse of the six line Mossbauer spectrum to a single line. This effect was studied as a function of r.f. field intensity. Appearance of r.f. sidebands in collapse spectrum was observed.

Influence of stress induced anisotropy on the RF collapse in ferromagnetic amorphous metals

Abstract Radio frequency collapse in Mossbauer spectra of ferromagnetic amorphous metals can be suppressed by the application of uniaxial external stresses. The stress induced anisotropy fields are calculated and are found to agree well with values deduced from the field dependence of the rf collapse at constant frequency.