Programmable Velocity equipment was used to perform a Mössbauer Thermal Scans to allow a quasi-continuous temperature study of the magnetic transition between the low-spin and a high-spin configurations in [Fe(Htrz)2(trz)](BF4) system. The material was studied both in bulk as in nanoparticles sample forms.Facultad de Ciencias ExactasInstituto de Física La PlataInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Cabrera, Alejandra Fabiana

Ceolín, Marcelo Raúl

Coronado Miralles, E.

Galan Mascaros, J. R.

Mendoza Zélis, Pedro

Monrabal Capilla, M.

Pasquevich, Alberto F.

Sánchez, Francisco Homero

Veiga, Alejandro Luis

Journal of Physics Conference Series

Pasquevich, Alberto Felipe

Servicio de Difusión de la Creación Intelectual

Journal of Physics: Conference SeriesRelated contenth a ■ ■ _ _ I _ ji _ _ _ | _ _ _ _ < i - - Mössbauer spectroscopy. Raman-and IR-Mössbauer th ©rm a I scan study of a spin crossover microscopy studies of hysteric behaviourin spincrossover systemssystem A Ahrens-Botzong, K Muffler, S M Stuppy et al.To cite this article: P Mendoza Zelis et al 2010 J. Phys.: Conf. Ser. 217 012017- Room temperature hvsteretic spin transition in 1D iron(ll) coordination polymersMarinela M DTrtu, Anil D Naik, Jacqueline Marchand-Brynaert et al.View the article online for updates and enhancements. - Mössbauer Spectroscopic Studies of z,3/Nd in frozen nitric acid solution M Nakada, J Wang, T Kitazawa et al.Recent citations- Resonance Raman Study of Spin- Crossover [Fe(Htrz)2 (trz)1(BF4 ) H2 O Particles Coated with GoldYeny A. Tobon et al- Triazole-Based One-Dimensional Spin- Crossover Coordination Polymers Olivier Roubeau- Smooth driving of Mössbauer electromechanical transducers A. Veiga et al¡booksBringing you innovative digital publishing with leading voices to create your essential collection of books in STEM research.Start exploring the collection - download the first chapter of every title for free.This content was downloaded from IP address 163.10.34.204 on 26/08/2019 at 19:03International Conference on the Applications of the Mössbauer Effect (ICAME 2009) IOP PublishingJournal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017Mössbauer thermal scan study of a spin crossover systemP Mendoza Zélis12, G A Pasquevich12, F H Sánchez12, A Veiga1, M Ceolin3, A F Cabrera12, E Coronado-Miralles4, M Monrabal-Capilla4, J R Galan-Mascaros4.1 Departamento de Física, FCE-UNLP, La Plata, Argentina2 Instituto de Física La Plata, CONICET,La Plata, Argentina3 Instituto de Investigaciones Físico-Químicas Teóricas y Aplicadas (UNLP-CONICET), La Plata, Argentina4 Instituto de Ciencias Moleculares, Universidad de Valencia, Valencia, EspañaE-mail: pmendoza@fisica.unlp.edu.arAbstract. Programmable Velocity equipment was used to perform a Mössbauer Thermal Scans to allow a quasi-continuous temperature study of the magnetic transition between the low-spin and a high-spin configurations in [Fe(Htrz)2(trz)](BF4) system. The material was studied both in bulk as in nanoparticles sample forms.1. IntroductionMössbauer Thermal Scans (MTS) were usually used to determine order temperatures [1,2]. Recently the technique was applied to obtain information on the temperature dependence of relative phase abundances, hyperfine and other spectrum parameters [3,4], In these works different scans at one selected Doppler energy were done. The recent development of Programmable Velocity Scaler equipments [5], which allow to measure at arbitrary energies and for arbitrary times, highly improved the versatility of MTS techniques [6],The experimental system developed in our laboratory allows the selection of Regions Of Interest (ROIs) in any spectral region, with a very high flexibility[7], while it undergoes changes due to the variation of an external parameter such as temperature, magnetic field, etc. The ROI can be composed of any number of points (up to 4096) with a freely selectable energy and live time for each point. We called the working mode of this equipment the Programmable Velocity Mode (PVM), to differentiate it from the conventional constant acceleration mode and constant velocity mode.In this work we show that PVM can be used to perform Mössbauer Thermal Scans allowing a quasi-continuous temperature study of a thermally activated transition. In this case we study a spin crossover between a low-spin (LS) and a high-spin (HS) configuration.Spin Crossover systems [8] are very interesting materials because of the ability to change their electronic state, between LS and HS configuration, under the influence of external stimuli (temperature, electromagnetic irradiation, pressure, etc.) being potential candidates e.g. for memory devices.Among them, the [Fe(Htrz)n(trz)3.n]Xm family (trz: triazole derivative) is a promising candidate for exhibiting bistability [9], For the specific case of [Fe(Htrz)2(trz)](BF4), the Fe(II) ions are coordinated by the ligands forming a 1-D polymeric structure exhibiting a cooperative spin transition from LS (5=0) to HS (5=2). Our study is performed with this material.©2010 IOP Publishing Ltd 1International Conference on the Applications of the Mössbauer Effect (ICAME 2009) TOP PublishingJournal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/0120172. Experimental procedure[Fe(Htrz)2(trz)](BF4) was prepared as bulk material and as 11 nm nanoparticles following the protocols described in reference [10] for compound la and using conventional reverse micelle techniques [11],The experimental setup for a MTS consists of a conventional pulse height selection branch, a commercial driving system and two recently developed NIM modules serially interfaced with a computer. The first one is a previously introduced programmable constant-velocity scaler [5] that replaces the usual multiscaler. This module allows the independent acquisition of every spectrum channel based on a constant-velocity strategy and consequently the acquisition of partial Mössbauer spectra in selected energy regions. The second module is an analog input/output interface used to record the temperature and to command a linear DC power source that is used to modify the temperature of the sample. Both NIM modules communicate serially with the PC that runs a high-level technical computing language that can interact directly with hardware. A previously developed interactive environment for data visualization and data analysis was used in the workstation. In this way the programmable scaler and the temperature control could be fully operated and re-programmed as required.The MTS and the conventional Mössbauer spectroscopy were obtained with a 25 mCi ^CoRh. Both calibrations were performed recording a complete ot-Fe spectrum at RT.3. Mössbauer spectroscopyThe LS and HS states of iron(II) can clearly be distinguished by Mössbauer spectroscopy by means of its hyperfine parameters (see figure 1). Both states are represented by a quadrupolar interaction but with a very different hyperfine parameters, while the LS state is characterized by an isomer shift of 0.42 mm/s and quadrupolar splitting of 0.27 mm/s at 298K, the HS state is characterized by an isomer shift of 0.97mm/s and quadrupolar splitting of 2.3 mm/s at 400K. Then these states can be clearly differentiated in the Mössbauer spectrum. It was noted that at temperatures beyond transition about 10% of the spectral area corresponds to LS phase.Velocity (mm/s)Figure 1. Mössbauer spectra of [Lc(11trz)2( trz)](13L|) bulk sample. The LS and HS states of iron(II) are clearly distinguished. Each state is represented by a quadrupolar interaction.4. Mössbauer Thermal ScansWe performed a Mössbauer thermal scan using a fixed ROI that was selected in order to include the patterns of the LS and HS phases, based on information previously obtained from Mössbauer Spectra taken at RT and 400 K. For the present case a ROI of 51 equally spaced points in the range from -1 to +3 mm/s, approximately centered at the isomer shift of the high temperature phase was chosen; and one additional point at an energy corresponding to background transmission (-8 mm/s) for control and normalization purposes was also incorporated. The ROI was periodically swept at 2 s/point while the sample was warmed up from RT to 411 K, and then cooled back to RT at rates of about ± 0.23 K/min. The whole experimental time was 16 h. Both scans of a [Fe(Htrz)2(trz)](BF4) bulk material absorber (6% effect at RT) are shown in figures 2-a and 2-b. This approach provided a detailed temperature and Doppler energy observation of the transition leading to a wealth of experimental information.2International Conference on the Applications of the Mössbauer Effect (1CAME 2009) IOP PublishingJournal of Physics: Conference Series 217 (2010) 012017 doi:10.1088/1742-6596/217/1/012017Figure 2. Mössbauer thermal scan (dots) for the [Fe(Htrz)2(trz)](BF4) bulk material absorber using a fixed ROI (51 points) in the range from -1 to +3 mm/s and one additional point at an energy corresponding to background transmission (-8 mm/s) not shown in the figure. The ROI was periodically swept at 2 s/point while the sample was warmed up (a) to 411 K from RT, and then cooled back (b) to RT at rates of about ± 0.23 K/min. The continuous lines are the level curves of the fitted surface.The whole set of MTS data was analyzed as an absorption surface F(T,v) against velocity and temperature using an appropriate function. This consists of two quadrupolar interactions, each one with a fixed line width, but with temperature dependent isomer shift (S(T) = So+ T Si ), quadrupolar splitting (A(9(T) = AO0 (1+T '2 )) and spectral areas. The spectra area temperature dependence was modeled considering the product of the Mossbauer-Lamb factor temperature dependence (assumed linear within the small scanned temperature interval) and the temperature evolution of the phases relative abundancesy(T).The results obtained in figures 2-a and 2-b confirm the presence of thermal hysteresis in the transition. This hysteresis is due to the metastability of the high temperature configuration. For the time being we have decided to ignore metastability and treat the spin crossover transition within an equilibrium approach. A two level system with energy difference E and multiplicities 1 and Q is proposed for the polymeric chain. The low spin configuration (5=0) has multiplicity 1, while the high spin one has multiplicity Q = ©A, where co = 3x(25+l) = 15 (assuming that t2g group is degenerate from where factor 3 arises[ 12]). N is the number of Fe atoms in the polymeric chain. Then3International Conference on the Applications of the Mössbauer Effect (ICAME 2009) IOP PublishingJournal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017fHS(T) = (1)1 + Qe,-F"T’We define the transition temperature T05 through the condition / (7,0J)=l/2 and the temperature transition width AT7 by f (Tos) AT=1 . From these, it follows that ios(i2) = «kAT AT(2)Since the transition presents hysteresis, at least two different T05 values will be required to reproduce the experimental data. However, the E and Q values on the heating up process are not very different from those of the cooling down one. Owing this, we may take them as representative of the physics of the problem. The fitting parameters corresponding to the temperature evolution of the two phases relative abundances are Eup (heating up), Edown (cooling down) and Q. The obtained values are: Eup = 4.1 eV, Edown = 4.5 eV , and Q = 7xl06" corresponding to 371K (ATup=10K) and 341K (ATdown=7K) for T05 in the heating up and cooling down respectively, and N~ 50.The experimental result and the level curves of the fitted surface corresponding to the warming and cooling process are shown in figure 2-a and 2-b. The level curves demonstrate the goodness of the fit.In addition, in figure 3 we present temperature intersects of the previous figure at different temperature to show the agreement between experimental data and the fitted surface. In each graph are shown: the values measured in an interval of ±2K around the specified temperature (open blue circles), the measure average in this temperature interval (filled red points) and the intersect of the fitted surface (black line). In these intersects the presence at high temperature of the previously mentioned remnant LS phase fraction was clearly observed (see for example the 382 K intersect). As this fraction was not observed to be temperature dependent it was not considered in the analysis of the absorption surface F(T,v) evolution.° ° ®o o * ' - - A "heating \♦ \.310K•A //) \ * \ /IM340K 340KAV370K 370KOO ° O o ° 8 -1 0 1 2 3A ¿AA-/ 4ÏV v cooling382KVelocity (mm/s)Figure 3. Temperature intersects of the MTS at different temperature. In each graph are shown the values measured in an interval of ±2K around the specified temperature (blue circles), the measure average in this temperature interval (red points) and the intersect of the fitted surface (black line).4International Conference on the Applications of the Mössbauer Effect (ICAME 2009) IOP PublishingJournal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017The Mössbauer Spectra of the nanoparticles sample (not shown) indicate that the hyperfine parameters of both samples are similar (isomer shift: 0.44 mm/s, quadrupolar splitting: 0.35 mm/s at 298K for the LS phase and isomer shift: 1.0 mm/s, quadrupolar splitting: 2.6 mm/s at 41 IK for the HS phase). Mössbauer thermal scan of the nanoparticles warmed up to 415 K from RT is shown in figure 4 (the cooling back to RT is not shown). The whole experimental time was 80 hs. A 47 channels ROI plus background, and a time/channel ratio of 8 seconds were chosen. The data are analyzed as a absorption surface against velocity and temperature using the mentioned function. The level curves of the fitted surface corresponding to the warming process are shown in figure 4. The experimental result confirm the presence of magnetic bistability even in nanoparticles samples. The values of T05 determined in the fitting procedure are 372 K and 341 K corresponding to the heating up and cooling down respectively.Figure 4. Mössbauer thennal scan of the nanoparticles wanned up from RT to 415K (dots). The continuous line are the level curves of the fitted surface.5. ConclusionsProgrammable Velocity Scaler equipment was used to perform Mössbauer Thermal Scans to follow up the magnetic transition through a quasi-continuous temperature study of the low-to-high spin transition of the [Fe(Htrz)2(trz)] (BF4) system. The study was made in bulk material and 11 nm nanoparticles. With information retrieved from conventional Mössbauer spectra, the ROI was chosen. Fitting the experimental data with an appropriate function, an absorption vs. energy®temperature surface was reconstructed. In this way a detailed quasi continuous observation of the spin thermal transition vs. temperature in terms of phases absorption spectral line intensities and positions was accomplished.References[1] Chien C L 1963 Phys. Rev. B 18 ppl003.[2] Gonser U, Meechan C J. Muir C J. WiedersichH 1963 J. Appl. Phys. 34 pp2373.[3] Mendoza Zélis P, Pasquevich G A, Sánchez F H, Martínez N, Veiga A 2002 Phys. Lett. A 298 pp 55.[4] Pasquevich G A, Mendoza Zélis P, Fernandez van Raap M B, Sánchez F H 2004 Physica B 31 pp369.[5] Veiga A, Martínez N, Mendoza Zélis P, Pasquevich G A, Sánchez F H 2006 Hyperfine Interact. 167 pp905.[6] Veiga A, Martínez N, Mendoza Zélis P, Pasquevich G A, Sánchez F H 2009 Hyperfine Interact. 188 ppl37.[7] Mendoza Zélis P, Pasquevich G A, Veiga A, Fernández van Raap M B and Sánchez F H 2009 HyperfineInteract. 195ppl61.[8] Gütlich P, van Koningsbruggcn P J. Renz F 2004 Struct. Bonding 107 pp27.[9] Haasnoot J G 2000 Coord. Chem. Rev.. 200 ppl31.[10] Krober J, Audiere J P, Claude R. Kahn O. Codjovi E, Haasnoot JG. Groliere F, Jay C. Bosseksou. A,Linares J. Varret F, Gonthier-Vasal A 1994 Chem.Matter. 6 ppl404.[11] Coronado E, Galán-Mascaros J R. Monrabal-Capilla M, Garcia-Martinez J, Pardo-Ibáñez P 2007Adv.Mater. 19 ppl359.[12] Koudriavtsev A B, Jameson R F, Linert W 2001 The Law of Mass Action (Berlin: Springer)5

Mössbauer thermal scan study of a spin crossover system

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Related content
h a ■ ■ _ _ I _ ji _ _ _ | _ _ _ _ < i - - Mössbauer spectroscopy. Raman-and IR-Mössbauer th ©rm a I scan study of a spin crossover microscopy studies of hysteric behaviour
in spincrossover systems
system A Ahrens-Botzong, K Muffler, S M Stuppy et al.
To cite this article: P Mendoza Zelis et al 2010 J. Phys.: Conf. Ser. 217 012017
- Room temperature hvsteretic spin 
transition in 1D iron(ll) coordination 
polymers
Marinela M DTrtu, Anil D Naik, Jacqueline 
Marchand-Brynaert et al.
View the article online for updates and enhancements. - Mössbauer Spectroscopic Studies of z,3/Nd in frozen nitric acid solution 
M Nakada, J Wang, T Kitazawa et al.
Recent citations
- Resonance Raman Study of Spin- 
Crossover [Fe(Htrz)2 (trz)1(BF4 ) H2 O 
Particles Coated with Gold
Yeny A. Tobon et al
- Triazole-Based One-Dimensional Spin- 
Crossover Coordination Polymers 
Olivier Roubeau
- Smooth driving of Mössbauer 
electromechanical transducers 
A. Veiga et al
¡books
Bringing you innovative digital publishing with leading voices 
to create your essential collection of books in STEM research.
Start exploring the collection - download the first chapter of 
every title for free.
This content was downloaded from IP address 163.10.34.204 on 26/08/2019 at 19:03
International Conference on the Applications of the Mössbauer Effect (ICAME 2009) IOP Publishing
Journal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017
Mössbauer thermal scan study of a spin crossover system
P Mendoza Zélis12, G A Pasquevich12, F H Sánchez12, A Veiga1, M Ceolin3, A F 
Cabrera12, E Coronado-Miralles4, M Monrabal-Capilla4, J R Galan-Mascaros4.
1 Departamento de Física, FCE-UNLP, La Plata, Argentina
2 Instituto de Física La Plata, CONICET,La Plata, Argentina
3 Instituto de Investigaciones Físico-Químicas Teóricas y Aplicadas (UNLP-CONICET), La 
Plata, Argentina
4 Instituto de Ciencias Moleculares, Universidad de Valencia, Valencia, España
E-mail: pmendoza@fisica.unlp.edu.ar
Abstract. Programmable Velocity equipment was used to perform a Mössbauer Thermal Scans 
to allow a quasi-continuous temperature study of the magnetic transition between the low-spin 
and a high-spin configurations in [Fe(Htrz)2(trz)](BF4) system. The material was studied both 
in bulk as in nanoparticles sample forms.
1. Introduction
Mössbauer Thermal Scans (MTS) were usually used to determine order temperatures [1,2]. Recently 
the technique was applied to obtain information on the temperature dependence of relative phase 
abundances, hyperfine and other spectrum parameters [3,4], In these works different scans at one 
selected Doppler energy were done. The recent development of Programmable Velocity Scaler 
equipments [5], which allow to measure at arbitrary energies and for arbitrary times, highly improved 
the versatility of MTS techniques [6],
The experimental system developed in our laboratory allows the selection of Regions Of Interest 
(ROIs) in any spectral region, with a very high flexibility[7], while it undergoes changes due to the 
variation of an external parameter such as temperature, magnetic field, etc. The ROI can be composed 
of any number of points (up to 4096) with a freely selectable energy and live time for each point. We 
called the working mode of this equipment the Programmable Velocity Mode (PVM), to differentiate 
it from the conventional constant acceleration mode and constant velocity mode.
In this work we show that PVM can be used to perform Mössbauer Thermal Scans allowing a 
quasi-continuous temperature study of a thermally activated transition. In this case we study a spin 
crossover between a low-spin (LS) and a high-spin (HS) configuration.
Spin Crossover systems [8] are very interesting materials because of the ability to change their 
electronic state, between LS and HS configuration, under the influence of external stimuli 
(temperature, electromagnetic irradiation, pressure, etc.) being potential candidates e.g. for memory 
devices.
Among them, the [Fe(Htrz)n(trz)3.n]Xm family (trz: triazole derivative) is a promising candidate for 
exhibiting bistability [9], For the specific case of [Fe(Htrz)2(trz)](BF4), the Fe(II) ions are coordinated 
by the ligands forming a 1-D polymeric structure exhibiting a cooperative spin transition from LS 
(5=0) to HS (5=2). Our study is performed with this material.
©2010 IOP Publishing Ltd 1
International Conference on the Applications of the Mössbauer Effect (ICAME 2009) TOP Publishing
Journal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017
2. Experimental procedure
[Fe(Htrz)2(trz)](BF4) was prepared as bulk material and as 11 nm nanoparticles following the 
protocols described in reference [10] for compound la and using conventional reverse micelle 
techniques [11],
The experimental setup for a MTS consists of a conventional pulse height selection branch, a 
commercial driving system and two recently developed NIM modules serially interfaced with a 
computer. The first one is a previously introduced programmable constant-velocity scaler [5] that 
replaces the usual multiscaler. This module allows the independent acquisition of every spectrum 
channel based on a constant-velocity strategy and consequently the acquisition of partial Mössbauer 
spectra in selected energy regions. The second module is an analog input/output interface used to 
record the temperature and to command a linear DC power source that is used to modify the 
temperature of the sample. Both NIM modules communicate serially with the PC that runs a high-level 
technical computing language that can interact directly with hardware. A previously developed 
interactive environment for data visualization and data analysis was used in the workstation. In this 
way the programmable scaler and the temperature control could be fully operated and re-programmed 
as required.
The MTS and the conventional Mössbauer spectroscopy were obtained with a 25 mCi ^CoRh. 
Both calibrations were performed recording a complete ot-Fe spectrum at RT.
3. Mössbauer spectroscopy
The LS and HS states of iron(II) can clearly be distinguished by Mössbauer spectroscopy by means of 
its hyperfine parameters (see figure 1). Both states are represented by a quadrupolar interaction but 
with a very different hyperfine parameters, while the LS state is characterized by an isomer shift of 
0.42 mm/s and quadrupolar splitting of 0.27 mm/s at 298K, the HS state is characterized by an isomer 
shift of 0.97mm/s and quadrupolar splitting of 2.3 mm/s at 400K. Then these states can be clearly 
differentiated in the Mössbauer spectrum. It was noted that at temperatures beyond transition about 
10% of the spectral area corresponds to LS phase.
Velocity (mm/s)
Figure 1. Mössbauer spectra of 
[Lc(11trz)2( trz)](13L|) bulk sample. The LS and 
HS states of iron(II) are clearly distinguished. 
Each state is represented by a quadrupolar 
interaction.
4. Mössbauer Thermal Scans
We performed a Mössbauer thermal scan using a fixed ROI that was selected in order to include the 
patterns of the LS and HS phases, based on information previously obtained from Mössbauer Spectra 
taken at RT and 400 K. For the present case a ROI of 51 equally spaced points in the range from -1 to 
+3 mm/s, approximately centered at the isomer shift of the high temperature phase was chosen; and 
one additional point at an energy corresponding to background transmission (-8 mm/s) for control and 
normalization purposes was also incorporated. The ROI was periodically swept at 2 s/point while the 
sample was warmed up from RT to 411 K, and then cooled back to RT at rates of about ± 0.23 K/min. 
The whole experimental time was 16 h. Both scans of a [Fe(Htrz)2(trz)](BF4) bulk material absorber 
(6% effect at RT) are shown in figures 2-a and 2-b. This approach provided a detailed temperature and 
Doppler energy observation of the transition leading to a wealth of experimental information.
2
International Conference on the Applications of the Mössbauer Effect (1CAME 2009) IOP Publishing
Journal of Physics: Conference Series 217 (2010) 012017 doi:10.1088/1742-6596/217/1/012017
Figure 2. Mössbauer thermal scan (dots) for the [Fe(Htrz)2(trz)](BF4) bulk 
material absorber using a fixed ROI (51 points) in the range from -1 to +3 
mm/s and one additional point at an energy corresponding to background 
transmission (-8 mm/s) not shown in the figure. The ROI was periodically 
swept at 2 s/point while the sample was warmed up (a) to 411 K from RT, 
and then cooled back (b) to RT at rates of about ± 0.23 K/min. The 
continuous lines are the level curves of the fitted surface.
The whole set of MTS data was analyzed as an absorption surface F(T,v) against velocity and 
temperature using an appropriate function. This consists of two quadrupolar interactions, each one 
with a fixed line width, but with temperature dependent isomer shift (S(T) = So+ T Si ), quadrupolar 
splitting (A(9(T) = AO0 (1+T '2 )) and spectral areas. The spectra area temperature dependence was 
modeled considering the product of the Mossbauer-Lamb factor temperature dependence (assumed 
linear within the small scanned temperature interval) and the temperature evolution of the phases 
relative abundancesy(T).
The results obtained in figures 2-a and 2-b confirm the presence of thermal hysteresis in the 
transition. This hysteresis is due to the metastability of the high temperature configuration. For the 
time being we have decided to ignore metastability and treat the spin crossover transition within an 
equilibrium approach. A two level system with energy difference E and multiplicities 1 and Q is 
proposed for the polymeric chain. The low spin configuration (5=0) has multiplicity 1, while the high 
spin one has multiplicity Q = ©A, where co = 3x(25+l) = 15 (assuming that t2g group is degenerate 
from where factor 3 arises[ 12]). N is the number of Fe atoms in the polymeric chain. Then
3
International Conference on the Applications of the Mössbauer Effect (ICAME 2009) IOP Publishing
Journal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017
fHS(T) = (1)
1 + Qe,-F"T’
We define the transition temperature T05 through the condition / (7,0J)=l/2 and the temperature 
transition width AT7 by f (Tos) AT=1 . From these, it follows that 
ios(i2) = «k
AT AT
(2)
Since the transition presents hysteresis, at least two different T05 values will be required to 
reproduce the experimental data. However, the E and Q values on the heating up process are not very 
different from those of the cooling down one. Owing this, we may take them as representative of the 
physics of the problem. The fitting parameters corresponding to the temperature evolution of the two 
phases relative abundances are Eup (heating up), Edown (cooling down) and Q. The obtained values are: 
Eup = 4.1 eV, Edown = 4.5 eV , and Q = 7xl06" corresponding to 371K (ATup=10K) and 341K 
(ATdown=7K) for T05 in the heating up and cooling down respectively, and N~ 50.
The experimental result and the level curves of the fitted surface corresponding to the warming and 
cooling process are shown in figure 2-a and 2-b. The level curves demonstrate the goodness of the fit.
In addition, in figure 3 we present temperature intersects of the previous figure at different 
temperature to show the agreement between experimental data and the fitted surface. In each graph are 
shown: the values measured in an interval of ±2K around the specified temperature (open blue circles), 
the measure average in this temperature interval (filled red points) and the intersect of the fitted 
surface (black line). In these intersects the presence at high temperature of the previously mentioned 
remnant LS phase fraction was clearly observed (see for example the 382 K intersect). As this fraction 
was not observed to be temperature dependent it was not considered in the analysis of the absorption 
surface F(T,v) evolution.
° ° ®o o * ' - - A "
heating \
♦ \.
310K
•A //
) \ * \ /
IM
340K 340K
A
V
370K 370K
OO ° O o ° 8 -1 0 1 2 3
A ¿AA-/ 4Ï
V v cooling
382K
Velocity (mm/s)
Figure 3. Temperature intersects of the MTS at 
different temperature. In each graph are shown the 
values measured in an interval of ±2K around the 
specified temperature (blue circles), the measure 
average in this temperature interval (red points) and 
the intersect of the fitted surface (black line).
4
International Conference on the Applications of the Mössbauer Effect (ICAME 2009) IOP Publishing
Journal of Physics: Conference Series 217 (2010) 012017 doi: 10.1088/1742-6596/217/1/012017
The Mössbauer Spectra of the nanoparticles sample (not shown) indicate that the hyperfine 
parameters of both samples are similar (isomer shift: 0.44 mm/s, quadrupolar splitting: 0.35 mm/s at 
298K for the LS phase and isomer shift: 1.0 mm/s, quadrupolar splitting: 2.6 mm/s at 41 IK for the HS 
phase). Mössbauer thermal scan of the nanoparticles warmed up to 415 K from RT is shown in figure 
4 (the cooling back to RT is not shown). The whole experimental time was 80 hs. A 47 channels ROI 
plus background, and a time/channel ratio of 8 seconds were chosen. The data are analyzed as a 
absorption surface against velocity and temperature using the mentioned function. The level curves of 
the fitted surface corresponding to the warming process are shown in figure 4. The experimental result 
confirm the presence of magnetic bistability even in nanoparticles samples. The values of T05 
determined in the fitting procedure are 372 K and 341 K corresponding to the heating up and cooling 
down respectively.
Figure 4. Mössbauer thennal scan of the 
nanoparticles wanned up from RT to 415K 
(dots). The continuous line are the level 
curves of the fitted surface.
5. Conclusions
Programmable Velocity Scaler equipment was used to perform Mössbauer Thermal Scans to follow up 
the magnetic transition through a quasi-continuous temperature study of the low-to-high spin transition 
of the [Fe(Htrz)2(trz)] (BF4) system. The study was made in bulk material and 11 nm nanoparticles. 
With information retrieved from conventional Mössbauer spectra, the ROI was chosen. Fitting the 
experimental data with an appropriate function, an absorption vs. energy®temperature surface was 
reconstructed. In this way a detailed quasi continuous observation of the spin thermal transition vs. 
temperature in terms of phases absorption spectral line intensities and positions was accomplished.
References
[1] Chien C L 1963 Phys. Rev. B 18 ppl003.
[2] Gonser U, Meechan C J. Muir C J. WiedersichH 1963 J. Appl. Phys. 34 pp2373.
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http://sedici.unlp.edu.ar/bitstream/handle/10915/82528/Documento_completo.pdf?sequence=1

Mössbauer thermal scan study of a spin crossover system

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