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Magnetic and Mössbauer study of some transition metal based nitroprussides
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) e753–e754
. Magnetic and Mossbauer study of some transition metal based nitroprussides ! b, Zuzana Mitroov ! a! a, Ma! ria Zentkova! a,*, Maria! n Mihalika, Igna! c Toth Anton Zentkoa, Martin Sendeka, Jozef Kova! Wa, Ma! ria Luka! Wova! a, Miroslav Mary&skoc, Marcel Miglierinib a
b
Institute of Experimental Physics Slovak Academy of Sciences, Watsonova 47, Ko$sice 043 53, Slovak Republic Slovak University of Technology, Department of Nuclear Physics & Technology, Ilkovicˇova 3, Bratislava 812 19, Slovak Republic c Institute of Physics Academy of Science of Czech Republic, Na Slovance 2 Prague, Czech Republic
Abstract Susceptibility data of freshly precipitated nitroprussides TM[Fe(CN)5NO] n H2O (TM=Mn, Fe, Co, Ni, Cu) follow very well modified Curie–Weiss law down to T ¼ 5 K indicating paramagnetic state; nitroprusside (NP) containing Zn is diamagnetic with a sign of paramagnetic contribution. Deviation from Curie–Weiss law and magnetization measurements on MnNP, FeNP and CoNP below T ¼ 5 K can indicate ferrimagnetic ordering at low temperatures. A hysteresis behaviour in ZFC and FC magnetisation with the temperature of bifurcation Tb ¼ 6 K was found for CoNP . and FeNP. Mossbauer spectra taken at room temperature (besides FeNP) consist of a single symmetric quadrupolesplit doublet with parameters d and D typical for FeII ions in octahedral sites. A more complicated spectrum of FeNP is a consequence of different Fe environments. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Xx; 76.80.+y . Keywords: Molecular magnets; Nitroprussides; Magnetic ordering; Hysteresis behaviour; Mossbauer spectrometry
Nitroprussides display very interesting photo-induced transitions to the long-lived metastable states [1]. An interesting light induced magnetic ordering effect was found in Ni[Fe(CN)5NO] n H2O [2]. The charge transfer from FeII to NO+ group, due to irradiation by light of the wavelength 475 nm, induces two antiferromagnetically coupled spins on FeII and NO+. In our contribu. tion we report on magnetic properties and Mossbauer spectroscopy results of Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+ NP in their freshly precipitated form. The investigated compounds were prepared by mixing of saturated aqueous solution of Na2[Fe(CN)5NO] with aqueous solution of divalent transition metal ions. The precipitated powder samples have been studied by X-ray *Corresponding author. Tel.: +421556338115; +421556336292. E-mail address: [email protected] (M. Zentkov!a).
fax:
diffraction and characterized as face-centred cubic (FCC) structures [3] (Mn2+, Fe2+, Co2+, Ni2+ and Zn2+), while Cu2+ salt has FCC structure with tetragonal distortion. The number n of H2O molecules was determined from TGA performed with SETARAM TG/DTA 92 equipment. Typical number of water molecules for freshly prepared samples is n ¼ 5: Magnetisation measurements were carried out with SQUID magnetometer (Quantum Design) in the magnetic field up to m0 H ¼ 5 T down to T ¼ 1:9 K. 57Fe . Mossbauer spectra were recorded at room and liquid nitrogen temperature by a constant acceleration spectrometer with a 57Co/Rh source. A tendency to saturation of magnetization was found on MnNP, FeNP and CoNP below T ¼ 5 K as it is demonstrated in Fig. 1 for CoNP sample. The value of saturated magnetisation Ms is determined by the electronic structure of transition metal ion TM, because
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.626
ARTICLE IN PRESS M. Zentkova! et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e753–e754 35
3.5
30
3.0 2.5
20 15 CoNP T=2K T=3K T=5K T=10 K
10 5 0 0
1
2
µ0H(T)
3
4
χ (m3/kg)x105
M(Am2/kg)
25
5
MnNP FeNP
CoNP NiNP
CuNP ZnNP
5.43 5.9 0.3 o3 1.853 0.017 Ferri?
2.26 3.8 1.7 o3 1.906 0.012 Ferri?
— 1.9 1.7 — 1.639 0.019 Par
2.96 4.9 1.8 o3 1.931 0.015 Ferri?
— 2.9 1.0 — 1.944 0.013 Par
— — — — 1.875 0.034 Dia+Par
the ground state of the FeII (S ¼ 2; L ¼ 0) in the octahedral environment is a magnetically inactive singlet. ms was determined from M vs. 1=m0 H dependence in extrapolation to infinite magnetic field. With increasing atomic number of TM the value of ms decreases as can be seen from Table 1. NP containing Zn2+ is diamagnetic with a pronounced paramagnetic component at low temperatures. The temperature dependence of susceptibility follows a modified Curie–Weiss law w ¼ w0 þ C=ðT YÞ down to T ¼ 5 K (see Fig. 2.). The effective magnetic moment meff decreases with increasing atomic number of TM ion (Table 1). Negative value of the paramagnetic Curie temperature (Table 1) indicates antiferromagnetic coupling in TMNP. Hysteresis behaviour between zero field cooled (ZFC) magnetisation and field cooled magnetisation (FC) with the temperature of bifurcation Tb B6 K was found for NP containing Fe and Co (inset in Fig. 2.). Deviation from modified Curie–Weiss law and a tendency to saturation of magnetization below T ¼ 5 K together with an antiferromagnetic coupling in samples with Mn, Fe and Co can indicate that these samples order ferrimagnetic at low temperatures. M.ossbauer spectra of Mn, Co, Ni, Cu, and Zn containing NPs depict quadrupole doublets characteristic for low spin FeII located in the nitroprusside anion.
Co[Fe(CN)5NO] . n H2O H=100 Oe H=50 Oe
0.06
1.5
0.04
0.02
1.0
0.00
4
6
8
10
12
14
T(K)
0.0 0
20
40
60
80
100
T(K) Fig. 2. Temperature dependence of the mass susceptibility. Solid lines represent the best fit to modified Curie–Weiss law. Inset shows hysteresis of magnetisation in ZFC and FC curves; arrows show the temperature of bifurcation.
D1
D2
D3
1.00 relative transmission
Table 1 . Magnetic and Mossbauer spectra parameters of TMNP (D-quadrupole splitting, d-isomer shift)
2.0
0.08
0.5
Fig. 1. Magnetisation curves taken on CoNP.
mS ðmB Þ meff ðmB Þ Y (K) TC (K) D (mm/s) d (mm/s) Order
MnNP FeNP CoNP NiNP CuNP
M(Am2/kg)
e754
D4 0.95
0.90
0.85 -2
-1
0 1 velocity (mm/s)
2
3
. Fig. 3. Mossbauer spectrum of Fe[Fe(CN)5NO] at 300 K.
Isomer shifts d (relative to Na2NP at 300 K) and quadrupole splitting D values are listed in Table 1. Four types of Fe sites (Fig. 3) were identified, in consistency with [4], in FeNP providing d and D values of 1.382, 1.397; 1.403, 2.589, and 1.384, 0.398 mm/s for D2, D3, and D4, correspondingly (for D1 parameters see Table 1). This work was supported by VEGA-2/1168/01, 1/ 8305/01 and APVT-20-009902 grants. SQUID magnetization measurements below T ¼ 5 K were taken in W. / by R. Gorzelniak. Trzebiatowski ILTS PAN Wroclaw
References [1] [2] [3] [4]
P. Gutlich, . et al., Coord. Chem. Rev. 219–221 (2001) 839. Z.Z. Gu, et al., J. Phys. Chem. 100 (1996) 18289. M. Sendek, et al., J. Elec. Eng. 53 (2002) 199. E. Reguera, et al., Hyperfine Interactions 77 (1993) 1.
Journal of Magnetism and Magnetic Materials 272–276 (2004) e753–e754
. Magnetic and Mossbauer study of some transition metal based nitroprussides ! b, Zuzana Mitroov ! a! a, Ma! ria Zentkova! a,*, Maria! n Mihalika, Igna! c Toth Anton Zentkoa, Martin Sendeka, Jozef Kova! Wa, Ma! ria Luka! Wova! a, Miroslav Mary&skoc, Marcel Miglierinib a
b
Institute of Experimental Physics Slovak Academy of Sciences, Watsonova 47, Ko$sice 043 53, Slovak Republic Slovak University of Technology, Department of Nuclear Physics & Technology, Ilkovicˇova 3, Bratislava 812 19, Slovak Republic c Institute of Physics Academy of Science of Czech Republic, Na Slovance 2 Prague, Czech Republic
Abstract Susceptibility data of freshly precipitated nitroprussides TM[Fe(CN)5NO] n H2O (TM=Mn, Fe, Co, Ni, Cu) follow very well modified Curie–Weiss law down to T ¼ 5 K indicating paramagnetic state; nitroprusside (NP) containing Zn is diamagnetic with a sign of paramagnetic contribution. Deviation from Curie–Weiss law and magnetization measurements on MnNP, FeNP and CoNP below T ¼ 5 K can indicate ferrimagnetic ordering at low temperatures. A hysteresis behaviour in ZFC and FC magnetisation with the temperature of bifurcation Tb ¼ 6 K was found for CoNP . and FeNP. Mossbauer spectra taken at room temperature (besides FeNP) consist of a single symmetric quadrupolesplit doublet with parameters d and D typical for FeII ions in octahedral sites. A more complicated spectrum of FeNP is a consequence of different Fe environments. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Xx; 76.80.+y . Keywords: Molecular magnets; Nitroprussides; Magnetic ordering; Hysteresis behaviour; Mossbauer spectrometry
Nitroprussides display very interesting photo-induced transitions to the long-lived metastable states [1]. An interesting light induced magnetic ordering effect was found in Ni[Fe(CN)5NO] n H2O [2]. The charge transfer from FeII to NO+ group, due to irradiation by light of the wavelength 475 nm, induces two antiferromagnetically coupled spins on FeII and NO+. In our contribu. tion we report on magnetic properties and Mossbauer spectroscopy results of Mn2+, Fe2+, Co2+, Ni2+, Cu2+ and Zn2+ NP in their freshly precipitated form. The investigated compounds were prepared by mixing of saturated aqueous solution of Na2[Fe(CN)5NO] with aqueous solution of divalent transition metal ions. The precipitated powder samples have been studied by X-ray *Corresponding author. Tel.: +421556338115; +421556336292. E-mail address: [email protected] (M. Zentkov!a).
fax:
diffraction and characterized as face-centred cubic (FCC) structures [3] (Mn2+, Fe2+, Co2+, Ni2+ and Zn2+), while Cu2+ salt has FCC structure with tetragonal distortion. The number n of H2O molecules was determined from TGA performed with SETARAM TG/DTA 92 equipment. Typical number of water molecules for freshly prepared samples is n ¼ 5: Magnetisation measurements were carried out with SQUID magnetometer (Quantum Design) in the magnetic field up to m0 H ¼ 5 T down to T ¼ 1:9 K. 57Fe . Mossbauer spectra were recorded at room and liquid nitrogen temperature by a constant acceleration spectrometer with a 57Co/Rh source. A tendency to saturation of magnetization was found on MnNP, FeNP and CoNP below T ¼ 5 K as it is demonstrated in Fig. 1 for CoNP sample. The value of saturated magnetisation Ms is determined by the electronic structure of transition metal ion TM, because
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.626
ARTICLE IN PRESS M. Zentkova! et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e753–e754 35
3.5
30
3.0 2.5
20 15 CoNP T=2K T=3K T=5K T=10 K
10 5 0 0
1
2
µ0H(T)
3
4
χ (m3/kg)x105
M(Am2/kg)
25
5
MnNP FeNP
CoNP NiNP
CuNP ZnNP
5.43 5.9 0.3 o3 1.853 0.017 Ferri?
2.26 3.8 1.7 o3 1.906 0.012 Ferri?
— 1.9 1.7 — 1.639 0.019 Par
2.96 4.9 1.8 o3 1.931 0.015 Ferri?
— 2.9 1.0 — 1.944 0.013 Par
— — — — 1.875 0.034 Dia+Par
the ground state of the FeII (S ¼ 2; L ¼ 0) in the octahedral environment is a magnetically inactive singlet. ms was determined from M vs. 1=m0 H dependence in extrapolation to infinite magnetic field. With increasing atomic number of TM the value of ms decreases as can be seen from Table 1. NP containing Zn2+ is diamagnetic with a pronounced paramagnetic component at low temperatures. The temperature dependence of susceptibility follows a modified Curie–Weiss law w ¼ w0 þ C=ðT YÞ down to T ¼ 5 K (see Fig. 2.). The effective magnetic moment meff decreases with increasing atomic number of TM ion (Table 1). Negative value of the paramagnetic Curie temperature (Table 1) indicates antiferromagnetic coupling in TMNP. Hysteresis behaviour between zero field cooled (ZFC) magnetisation and field cooled magnetisation (FC) with the temperature of bifurcation Tb B6 K was found for NP containing Fe and Co (inset in Fig. 2.). Deviation from modified Curie–Weiss law and a tendency to saturation of magnetization below T ¼ 5 K together with an antiferromagnetic coupling in samples with Mn, Fe and Co can indicate that these samples order ferrimagnetic at low temperatures. M.ossbauer spectra of Mn, Co, Ni, Cu, and Zn containing NPs depict quadrupole doublets characteristic for low spin FeII located in the nitroprusside anion.
Co[Fe(CN)5NO] . n H2O H=100 Oe H=50 Oe
0.06
1.5
0.04
0.02
1.0
0.00
4
6
8
10
12
14
T(K)
0.0 0
20
40
60
80
100
T(K) Fig. 2. Temperature dependence of the mass susceptibility. Solid lines represent the best fit to modified Curie–Weiss law. Inset shows hysteresis of magnetisation in ZFC and FC curves; arrows show the temperature of bifurcation.
D1
D2
D3
1.00 relative transmission
Table 1 . Magnetic and Mossbauer spectra parameters of TMNP (D-quadrupole splitting, d-isomer shift)
2.0
0.08
0.5
Fig. 1. Magnetisation curves taken on CoNP.
mS ðmB Þ meff ðmB Þ Y (K) TC (K) D (mm/s) d (mm/s) Order
MnNP FeNP CoNP NiNP CuNP
M(Am2/kg)
e754
D4 0.95
0.90
0.85 -2
-1
0 1 velocity (mm/s)
2
3
. Fig. 3. Mossbauer spectrum of Fe[Fe(CN)5NO] at 300 K.
Isomer shifts d (relative to Na2NP at 300 K) and quadrupole splitting D values are listed in Table 1. Four types of Fe sites (Fig. 3) were identified, in consistency with [4], in FeNP providing d and D values of 1.382, 1.397; 1.403, 2.589, and 1.384, 0.398 mm/s for D2, D3, and D4, correspondingly (for D1 parameters see Table 1). This work was supported by VEGA-2/1168/01, 1/ 8305/01 and APVT-20-009902 grants. SQUID magnetization measurements below T ¼ 5 K were taken in W. / by R. Gorzelniak. Trzebiatowski ILTS PAN Wroclaw
References [1] [2] [3] [4]
P. Gutlich, . et al., Coord. Chem. Rev. 219–221 (2001) 839. Z.Z. Gu, et al., J. Phys. Chem. 100 (1996) 18289. M. Sendek, et al., J. Elec. Eng. 53 (2002) 199. E. Reguera, et al., Hyperfine Interactions 77 (1993) 1.