This work was supported by the Slovak Research and Development Agency under the contracts No. APVV-16-0079 and APVV-15-0621, grants VEGA 1/0182/16 and VEGA 2/0082/17, and the internal IGA grant of Palack&#253; University (IGA_PrF_2018_002). We are grateful to R. R&#252;ffer (ESRF, Grenoble) for assistance with the synchrotron experiments.

1. Preparation of a MG
NOTE: To demonstrate a broad range of diagnostic capabilities of NFS in combination with M&#246;ssbauer spectrometry, an appropriate MG composition was designed, namely (Fe3Co1)76Mo8Cu1B15 (at.%). This system shows the magnetic transition from the ferromagnetic to paramagnetic state below the onset of crystallization. Moreover, crystallites that emerge during the first crystallization step form bcc-Fe,Co pha...

<ol>
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The authors have nothing to disclose.

Ex situ M&#246;ssbauer effect experiments describe a steady situation which is encountered in the investigated MG after the applied heat treatment. Each spectrum was collected for a duration of several hours at room temperature. Thus, the evolution of the originally amorphous structure was followed as a function of annealing conditions. Because M&#246;ssbauer spectrometry is sensitive to hyperfine interactions acting upon the resonant nuclei, faint details of structural and/or magnetic modifications induced by e...

Iron-based MGs prepared by rapid quenching of a melt represent industrially attractive materials with numerous practical applications1. Especially since their magnetic properties are often superior to conventional (poly)crystalline alloys2,3. To better benefit from their advantageous parameters, their response to elevated temperatures should be known. With increasing temperature, the amorphous structure relaxes and, finally, the crystallization starts. In some types of MGs, this can lead to the deterioration of their magnetic parameters and, consequently, poorer performance. There are, however, several families of iron-based MGs with special compositions4,5,6,7 in which the newly formed crystalline grains are very fine, typically below about 30 nm in size. The nanocrystals stabilize the structure and thus, preserve acceptable magnetic parameters over a wide temperature range8,9. These are the so-called nanocrystalline alloys (NCA).
The long-term performance reliability of MGs, especially under elevated temperatures and/or tough conditions (ionizing radiation, corrosion, etc.) demands thorough knowledge of their behavior and individual physical parameters. Because MGs are amorphous, the assortment of analytical techniques that are suitable for their characterization is rather limited. For example, diffraction methods provide broad and featureless reflections that can be used only for the verification of amorphicity.
It is noteworthy that several, usually indirect methods exist that provide fast and non-destructive characterization of MGs (e.g., magnetostrictive delay line sensing principle). This method provides fast characterization of structural and stress states including the presence of inhomogeneities. It was advantageously applied to fast and non-destructive characterization along the whole length of MG ribbons10,11.
More detailed insight into disordered structural arrangement can be achieved via hyperfine interactions that sensitively reflect the local atomic arrangement of the resonant atoms. Moreover, variations in topological and chemical short-range order can be revealed. In this respect, the methods like nuclear magnetic resonance (NMR) spectrometry and/or M&#246;ssbauer spectrometry, both performed on 57Fe nuclei, should be considered12,13. While the former method provides response exclusively to magnetic dipole hyperfine interactions, the latter is sensitive also to the electric quadrupole interactions. Thus, M&#246;ssbauer spectrometry makes simultaneously available information on both the structural arrangement and magnetic states of the resonant iron nuclei14.
Nevertheless, to achieve reasonable statistics, the acquisition of a M&#246;ssbauer spectrum usually takes several hours. This restriction should be considered especially when temperature-dependent experiments are envisaged. Elevated temperature that is applied during the experiment causes structural modifications in the investigated MGs15. Consequently, only ex situ experiments performed at room temperature upon samples that were first annealed at certain temperature and then returned to ambient conditions provide reliable results.
The evolution of MG structures during heat treatment is routinely studied by analytical techniques which enable rapid data acquisition as for example X-ray diffraction of synchrotron radiation (DSR), differential scanning calorimetry (DSC), or magnetic measurements. Though in situ experiments are possible, the obtained information concerns either structural (DSR, DSC) or magnetic (magnetic data) features. However, in the case of DSC (and magnetic measurements) the identification of the type of (nano)grains that emerge during the crystallization is not possible. On the other hand, DSR data do not indicate the magnetic states of the investigated system. A solution to this situation is a technique that makes use of hyperfine interactions: NFS of synchrotron radiation16. It belongs to a group of methods that exploits nuclear resonant scattering processes17. Due to extremely high brilliance of radiation obtained from the third generation of synchrotrons, temperature NFS experiments under in situ conditions became feasible18,19,20,21,22,23.
Both M&#246;ssbauer spectrometry and NFS are governed by the same physical principles related to nuclear resonance among energy levels of 57Fe nuclei. Nevertheless, while the former scans hyperfine interactions in the energy domain, the latter provides interferograms in the time domain. In this way, the results obtained from both methods are equivalent and complementary. To evaluate the NFS data, a reasonable physical model must be established. This challenging task can be accomplished by the help of M&#246;ssbauer spectrometry which provides the first estimate. Complementarity between these two methods means that in situ NFS inspects transient states and M&#246;ssbauer spectrometry reflects the stable states, viz. the initial and/or the final state of a material studied ex situ.
This article describes in detail selected applications of these two less common methods of nuclear resonances: here, we apply them to the investigation of structural modifications that occur in a (Fe2.85Co1)77Mo8Cu1B14 MG exposed to heat treatment. We hope that this article attracts the interest of researchers to use these techniques for the investigation of similar phenomena and eventually with different types of materials.

<table border="0" cellpadding="0" cellspacing="0" width="728">
	<tbody>
		<tr height="30">
			<td height="30" style="height:30px;width:216px;">stable isotope, 57Fe</td>
			<td style="width:147px;">Isoflex USA</td>
			<td style="width:119px;">iron-57</td>
			<td style="width:247px;">metallic form</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">standard eletrolytic Fe, 99.95 %</td>
			<td style="width:147px;">Sigma Aldrich (Merck)</td>
			<td style="width:119px;">1.03819</td>
			<td>fine powder</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">electrolytic Co, 99.85 %</td>
			<td style="width:147px;">Sigma Aldrich (Merck)</td>
			<td style="width:119px;">1.12211</td>
			<td>fine powder</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">electrolytic Cu, 99.8 %</td>
			<td style="width:147px;">Sigma Aldrich (Merck)</td>
			<td style="width:119px;">1.02703</td>
			<td>fine powder</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">electrolytic Mo, 99.95 %</td>
			<td style="width:147px;">Sigma Aldrich (Merck)</td>
			<td style="width:119px;">1.12254</td>
			<td>fine powder</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">crystalline B, 99.95 %</td>
			<td style="width:147px;">Sigma Aldrich (Merck)</td>
			<td style="width:119px;">266620</td>
			<td>crystalline</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">calibration foil for M&#246;ssbauer spectrometry, bcc-Fe</td>
			<td style="width:147px;">GoodFellow</td>
			<td style="width:119px;">564-385-23</td>
			<td>foil 0.0125 mm, purity 99.85 %</td>
		</tr>
		<tr height="44">
			<td height="44" style="height:44px;width:216px;">HNO3 acid, ANALPURE Ultra</td>
			<td style="width:147px;">Analytika Praha, Czech Republic</td>
			<td style="width:119px;">UAc0061a</td>
			<td>concentration 67 %, volume 500 mL</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">spectrometer for atomic absorption spectrometry</td>
			<td style="width:147px;">Perkin Elmer 1100, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:216px;">spectrometer for optical emmission spectrometry with inductively coupled plasma</td>
			<td style="width:147px;">Jobin Yvon 70 Plus, France</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">X-ray diffractometer</td>
			<td style="width:147px;">Bruker D8 Advance, USA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:216px;">differential scanning calorimeter</td>
			<td style="width:147px;">Perkin Elmer DSC 7, Germany</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

methods of ex situ and in situ investigations of structural transformations: the case of crystallization of metallic glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic glasses (MGs). Despite their amorphous nature, the identification of hyperfine interactions unveils faint structural modifications. For this purpose, we have employed two techniques that utilize nuclear resonance among nuclear levels of a stable 57Fe isotope, namely M&#246;ssbauer spectrometry and nuclear forward scattering (NFS) of synchrotron radiation. The effects of heat treatment upon (Fe2.85Co1)77Mo8Cu1B14 MG are discussed using the results of ex situ and in situ experiments, respectively. As both methods are sensitive to hyperfine interactions, information on structural arrangement as well as on magnetic microstructure is readily available. M&#246;ssbauer spectrometry performed ex situ describes how the structural arrangement and magnetic microstructure appears at room temperature after the annealing under certain conditions (temperature, time), and thus this technique inspects steady states. On the other hand, NFS data are recorded in situ during dynamically changing temperature and NFS examines transient states. The use of both techniques provides complementary information. In general, they can be applied to any suitable system in which it is important to know its steady state but also transient states.

The XRD pattern in Figure 2 exhibits broad featureless diffraction peaks. The observed reflections demonstrate that the produced ribbon of the (Fe2.85Co1)77Mo8Cu1B14 MG is XRD amorphous.
Due to its sensitivity, XRD has some limitations in unveiling surface crystallization. The presence of crystallites amounting to less than about 2-3%...

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Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

Here, we present a protocol to describe ex situ and in situ investigations of structural transformations in metallic glasses. We employed nuclear-based analytical methods which inspect hyperfine interactions. We demonstrate the applicability of M&#246;ssbauer spectrometry and nuclear forward scattering of synchrotron radiation during temperature-driven experiments.

Methods of Ex Situ and In Situ Investigations of Structural Transformations: The Case of Crystallization of Metallic Glasses

We demonstrate the use of two nuclear-based analytical methods that can follow the modifications of microstructural arrangement of iron-based metallic ...

This method can help answer key questions on the evolution of crystallization in iron-based metallic glasses with respect to varying time and/or temperature. The main advantage of this procedure is the use of two complementary nuclear-based analytical methods that can follow structural and magnetic transformations through hyperfine interactions. Mossbauer spectroscopy performed ex situ describes how the structural arrangement and magnetic microstructure appears after annealing at certain temperature and time, so it reflects a static situation.The method of nuclear forward scattering of synchrotron radiation provides data which are recorded in situ during dynamically changing temperature and thus inspects transient states. Demonstrating the procedure will be Dr.Irena Janatova, a junior research fellow from our laboratory. First cast a previously-prepared melt upon the rotating quenching wheel of an apparatus for planar flow casting under ambient conditions.Check the amorphous nature of the produced ribbons by performing X-ray diffraction in Bragg-Brentano geometry. Use a copper anode and record the diffraction pattern from 20 to 100 degrees of 2-theta with an angular step of 0.05 degrees and acquisition of 20 seconds for one point. Next prepare small pieces of the produced ribbons with a total mass of about three to five milligrams and place them into a DSC instrument.Perform the DSC experiment with a temperature ramp of 10 Kelvin per minute at a temperature range of 50 to 700 degrees Celsius under argon atmosphere. Determine the temperature of the onset of crystallization, which is taken at the kink of the most pronounced peak on the DSC curve. Choose five temperatures of annealing that cover both the pre-crystallization and crystallization regions on the DSC for further ex situ annealing.Following this, prepare five groups of seven-centimeter long pieces of the as-quenched ribbon. For ex situ annealing, set the destination temperature on a furnace and wait for 15 minutes for its stabilization. Following this, insert pieces of the ribbon into the evacuated and thermally-stabilized zone by opening a seven to 10-millimeter gap between the two blocks and sliding the ribbons directly into the center of the heated zone.Close the gap immediately so that the temperature of the sample achieves the furnace temperature in less than five seconds within a 0.1 Kelvin difference. After annealing, remove the heated ribbons and place them on a cold substrate inside the vacuum system to ensure fast cooling of the samples to room temperature. Prepare six to eight pieces of one-centimeter long ribbons for each sample for Mossbauer spectrometry experiments.Assemble the ribbons side-by-side using adhesive tape over the ends of the ribbons. Attach them to an aluminum holder to form a compact area of about one by one centimeters squared. Note the different appearance of both sides of the ribbons.Be sure that all ribbons are positioned on the aluminum holder with the same side upwards. Next insert the aluminum holder with the sample into the detector of the instrument. Prior to the measurement, thoroughly wash the inner detector volume with a stream of the detection gas for 10 to 15 minutes to expel all residual air.After washing, adjust the gas flow through the detector by a needle valve to three milliliters per minute. Next connect a high voltage to the detector. Record the CEMS and CXMS Mossbauer spectra using a constant acceleration spectrometer equipped with a Cobalt 57 radioactive source embedded in a rhodium matrix.Operate the spectrometer with a gas detector at room temperature according to the manual. For NFS experiments, place an approximately six-millimeter long ribbon of the investigated metallic glass in a vacuum furnace. Following this, record the NFS time-domain patterns during continuous heating of the sample to a temperature of up to 700 degrees Celsius with a ramp of 10 degrees per minute, using one-minute time intervals for acquisition of experimental data during the entire in situ annealing process.Finally, evaluate the NFS experimental data using suitable software. Mossbauer spectrometry allows direct identification of the type of structural arrangement, specifically crystalline versus amorphous as shown here. CEMS spectra taken from the air and wheel sides of the ribbons are displayed here.They show increasing contribution of the crystalline components after ex situ annealing. Comparison of the amounts of crystallites from CEMS and CXMS techniques is shown here. The crystallization starts after annealing at 410 degrees Celsius.NFS patterns that contain in time domain the same information on hyperfine interactions as Mossbauer spectra in energy domain but are recorded over a shorter time are shown here. The contour plot of NFS time domain patterns recorded during in situ heating of as-quenched ribbons is shown here. It exhibits a magnetic transition at the Curie temperature and the onset of crystallization.Examples of NFS patterns are shown here. The evolution of the total relative amount of nanocrystals with temperature is shown here. The onset of crystallization is marked with TX1.Total number of counts of the individual NFS time domain patterns with respect to the temperature of the in situ NFS experiment show three well distinguished regions that evolve during dynamically changing temperature. Mossbauer spectrometry unveils fine details of structural and/or magnetic transformations induced by heat treatment. However, the time needed for recording one spectrum can extend over several hours, which limits this technique to ex situ experiments.Using ex situ Mossbauer experiments, we can investigate the local structure and magnetic arrangement in a material under static conditions. These can be inspected before and/or after temperature treatment. Following the procedure of nuclear forward scattering, rapid data acquisition is ensured by extremely brilliant synchrotron radiation.Thus, in situ experiments can be performed during temperature treatment and immediate states of a material can be inspected under dynamic conditions. After watching this video, you should have a good understanding of benefits of the in situ nuclear forward scattering technique of synchrotron radiation. It is complementary with ex situ Mossbauer spectroscopy from the viewpoint of the obtained results and conditions under which they are achieved.These techniques pave the way for researchers in other fields that are associated with structural and/or magnetic transitions, especially when existence of intermediate states is foreseen.

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8.4K visualizações.  Slovak University of Technology in Bratislava, Slovakia. This method can help answer key questions on the evolution of crystallization in iron-based metallic glasses with respect to varying time and/or temperature. The main advantage of this procedure is the use of two complementary nuclear-based analytical methods that can follow structural and magnetic transformations through hyperfine interactions. Mossbauer spectroscopy performed ex situ describes how the structural arrangement and magnetic microstructure appears after annealing at certain temp...