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Mo¨ssbauer study of iron sulfides doped with 3d-transition metals
Solid State Communications 135 (2005) 327–329 www.elsevier.com/locate/ssc
Mo¨ssbauer study of iron sulfides doped with 3d-transition metals Hyo Duk Nama, Eng Chan Kimb,*, Jong Soo Hanb a
School of Electronical Engineering and Computer Science, Yeungnam University, Gyongsan 712-749, South Korea b Department of Physics, Yeungnam University, Gyongsan 712-749, South Korea Received 28 January 2005; received in revised form 15 April 2005; accepted 2 May 2005 by J.A. Brum Available online 11 May 2005
Abstract It is found by Mo¨ssbauer measurements on M0.025Fe0.975S (MZSc, Ti, V, Cr, Mn, Co, Ni, Cu) that the 3d-transition metal impurities profoundly affect both the crystallographic and spin rotation transitions of iron sulfide. It is noteworthy that both V0.025Fe0.975S and Co0.025Fe0.975S have Morin transition temperatures TM which are distinctly different from that of FeS; furthermore, the directions of changes of TM are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. A vanadium impurity of 2.5% of the metal atoms in the iron sulfide makes the crystallographic transition take place rapidly in a narrow temperature region of about 15 K, while the a transition in FeS takes place over a wide temperature range of about 200 K. It is also found that the a transition for V0.025Fe0.975S has a hysteresis width of 5 K. q 2005 Elsevier Ltd. All rights reserved. PACS: 76.80Cy; 76.; 77.80Bh Keywords: A. 3d-Transition metal; A. Iron sulfide; D. Transition
Iron sulfide FeS exhibits interesting magnetic and crystallographic phase transitions. In the neighborhood of Tay400 K, a crystallographic phase transition appears, usually called the a transition. Bertaut [1] has shown that FeS exists with a hexagonal NiAs structure above Ta and transforms below Ta to a hexagonal superstructure having a unit cell six times as large in volume as that of the NiAs structure above Ta. Magnetic-susceptibility and neutron-diffraction measurements [2–4] show that the FeS is antiferromagnetic with a Ne´el temperature of about 600 K and that the spin direction changes from perpendicular to parallel with the c axis below Ta. However, Sparks, Mead, and Komoto [3] demonstrated through more accurate neutron-diffraction measurements
* Corresponding author. Tel.: C82 53 810 2343; fax: C82 53 810 4616. E-mail address: [email protected] (E.C. Kim).
0038-1098/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2005.05.003
that for Fe0.996S the spin-rotation transition (the Morin transition) takes place at a temperature TM higher by 31 K than Ta. Similar independence of the Morin and a transitions was reported by Thiel and van den Berg [5] using Mo¨ssbauer measurements for Fe0.996S, though they found that TM was lower by 28 K than Ta in contrast to the other results [6–8]. The purpose of this research is to report briefly the effects of 3d-transition metal ions on the a and Morin (spin-flip) transitions as well as on the super-exchange interactions in iron sulfide. M0.025Fe0.975S (MZSc, Ti, V, Cr, Mn, Co, Ni, Cu) samples were prepared by direct reaction of the elements (of high purity, better than 99.995%). Mixtures of the proper proportions of the elements sealed in evacuated quartz ampoules were heated to 600 8C for 1 day, to 1000 8C for 3 days, and then quenched down to room temperature. In order to obtain homogeneous material it was necessary grind the sample after the first firing and to press the powder into a pellet before annealing it for a
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H.D. Nam et al. / Solid State Communications 135 (2005) 327–329
second time in an evacuated and sealed quartz ampoule. A third firing similar to the second one was required to get the single-phase samples. All the samples were 57Fe enriched to 5 at.% of the metal atoms for Mo¨ssbauer measurements. Mo¨ssbauer spectra were recorded using a conventional Mo¨ssbauer spectrometer of the electromechanical type with a 57Co source in a rhodium matrix. To produce a uniform thickness over the area of Mo¨ssbauer absorber, each sample was mixed with boron nitride powder and clamped between thin boron nitride plates. Examination of the samples by X-ray diffraction at room temperature showed that each sample crystallized in a single phase with a hexagonal structure. Table 1 shows the hexagonal lattice parameters ao and Co for various M0.025Fe0.975S. It is evident that there is no definite relationship between the lattice parameters and the number of 3d electrons. However, it is noteworthy that V0.025Fe0.975S and Co0.025Fe0.975S have lattice parameters which are distinctly different from those of FeS; furthermore, the directions of changes of the lattice parameters are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. ao of V0.025Fe0.975S is much less than that of FeS, while ao of Co0.025Fe0.975S is much larger than that of FeS. However, Co of V0.025Fe0.975S is larger than that of FeS whereas Co of Co0.025Fe0.975S is less than that of FeS. Mo¨ssbauer spectra of the M0.025Fe0.975S samples were taken at various temperatures ranging between liquid nitrogen temperature and 600 K. Using a least-squares computer program, one set or two of the six Lorentzian lines were fitted to the Mo¨ssbauer spectra below the Ne´el temperature. Ta was obtained from the temperature dependence of the magnetic hyperfine field Hhf for M0.025Fe0.975S in Mo¨ssbauer parameters. When the crystallographic phase transition appears, the magnetic hyperfine fields for the two phases have different values, respectively, at Ta. TM was got from the temperature dependence of the quadrupole splitting EQ for M0.025Fe0.975S in Mo¨ssbauer parameters. The quadrupole shift jumps abruptly from minus to plus value at about TM corresponding to a change Table 1 Lattice parameters of M0.025Fe0.975S (MZSc, Ti, V, Cr, Mn, Co, Ni, Cu) M(3dn) 1
Sc(3d ) Ti(3d2) V(3d3) Cr(3d4) Mn(3d5) Fe(3d6) Co(3d7) Ni(3d8) Cu(3d9) a
˚) ao (A 5.9702 5.9692 5.9462 5.9792 5.9672 5.9682 5.9912 5.9652 5.9882
˚) Co (A a
11.695 11.695 11.835 11.735 11.725 11.745 11.545 11.715 11.665
Subscript below each number indicates estimated error in the last digit.
Fig. 1. Compositional dependence of Ne´el temperature TN, a transition temperature Ta, and the Morin transition temperature TM.
in the spin-rotation with increasing temperature. It can be seen in Fig. 1 that both the Ne´el temperature TN and the a-transition temperature Ta are almost unaffected by the 3dtransition metal impurities. In another words, both the superexchange interaction and the superstructure transition are insensitive to the number of 3d electrons of the transitionmetal impurities. However, the spin-rotation transition is very sensitive to the kind of impurities as can be seen in Fig. 1. It is noteworthy that both V0.025Fe0.975S and Co0.025Fe0.975S have Morin transition temperatures TM which are distinctly different from that of FeS; furthermore, the directions of changes of TM are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. TM of V0.025Fe0.975S is higher by 80 K than that of FeS while TM of Co0.025Fe0.975S is lower by 200 K than that of FeS. Comparison of the Morin transition temperatures with the lattice parameters for V0.025Fe0.975S and Co0.025Fe0.975S shows that there seems to be some correlation between the spin-rotation and the lattice parameters. It is very interesting that the crystallographic transition is independent of the lattice parameters while the spin-rotation transition is dependent on them. It is also noted that the crystallographic phase transition for V0.025Fe0.975S takes place a narrow temperature region of about 15 K more rapidly than that for other M0.025Fe 0.975S; furthermore, the a transition for V0.025Fe0.975S has a hysteresis [5] width of 4 K, whereas no hysteresis was observed for FeS. The sharpening of the crystallographic transition due to the vanadium impurities is in marked contrast to the broadening of the coexistence region by Co or Cr impurities.
Acknowledgements This research was supported by the Yeungnam University research grants in 2004.
H.D. Nam et al. / Solid State Communications 135 (2005) 327–329
References [1] F. Bertaut, Bull. Soc. Fr. Mineral. Crystallogr. 79 (1956) 276. [2] E. Hirahara, M. Murakami, J. Phys. Chem. Solids 7 (1958) 281. [3] J.T. Sparks, W. Mead, A.J. Kirschbaum, W. Marshall, J. Appl. Phys. 31 (1960) 356S. [4] A.F. Andresen, P. Torbo, Acta Chem. Scand. 21 (1967) 2841.
329
[5] R.C. Thiel, C.B. van den Berg, Phys. Status Solidi 29 (1968) 837. [6] J.T. Sparks, W. Mead, T. Komoto, J. Phys. Soc. Jpn. 17 (Suppl. B1) (1962) 249. [7] K.S. Baek, K.Y. Park, H.J. Kim, H.N. Ok, Phys. Rev. B 41 (1990) 9024. [8] H.N. Ok, K.S. Baek, H.J. Kim, J. Korean Phys. Soc. 25 (1992) 447.
Mo¨ssbauer study of iron sulfides doped with 3d-transition metals Hyo Duk Nama, Eng Chan Kimb,*, Jong Soo Hanb a
School of Electronical Engineering and Computer Science, Yeungnam University, Gyongsan 712-749, South Korea b Department of Physics, Yeungnam University, Gyongsan 712-749, South Korea Received 28 January 2005; received in revised form 15 April 2005; accepted 2 May 2005 by J.A. Brum Available online 11 May 2005
Abstract It is found by Mo¨ssbauer measurements on M0.025Fe0.975S (MZSc, Ti, V, Cr, Mn, Co, Ni, Cu) that the 3d-transition metal impurities profoundly affect both the crystallographic and spin rotation transitions of iron sulfide. It is noteworthy that both V0.025Fe0.975S and Co0.025Fe0.975S have Morin transition temperatures TM which are distinctly different from that of FeS; furthermore, the directions of changes of TM are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. A vanadium impurity of 2.5% of the metal atoms in the iron sulfide makes the crystallographic transition take place rapidly in a narrow temperature region of about 15 K, while the a transition in FeS takes place over a wide temperature range of about 200 K. It is also found that the a transition for V0.025Fe0.975S has a hysteresis width of 5 K. q 2005 Elsevier Ltd. All rights reserved. PACS: 76.80Cy; 76.; 77.80Bh Keywords: A. 3d-Transition metal; A. Iron sulfide; D. Transition
Iron sulfide FeS exhibits interesting magnetic and crystallographic phase transitions. In the neighborhood of Tay400 K, a crystallographic phase transition appears, usually called the a transition. Bertaut [1] has shown that FeS exists with a hexagonal NiAs structure above Ta and transforms below Ta to a hexagonal superstructure having a unit cell six times as large in volume as that of the NiAs structure above Ta. Magnetic-susceptibility and neutron-diffraction measurements [2–4] show that the FeS is antiferromagnetic with a Ne´el temperature of about 600 K and that the spin direction changes from perpendicular to parallel with the c axis below Ta. However, Sparks, Mead, and Komoto [3] demonstrated through more accurate neutron-diffraction measurements
* Corresponding author. Tel.: C82 53 810 2343; fax: C82 53 810 4616. E-mail address: [email protected] (E.C. Kim).
0038-1098/$ - see front matter q 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.ssc.2005.05.003
that for Fe0.996S the spin-rotation transition (the Morin transition) takes place at a temperature TM higher by 31 K than Ta. Similar independence of the Morin and a transitions was reported by Thiel and van den Berg [5] using Mo¨ssbauer measurements for Fe0.996S, though they found that TM was lower by 28 K than Ta in contrast to the other results [6–8]. The purpose of this research is to report briefly the effects of 3d-transition metal ions on the a and Morin (spin-flip) transitions as well as on the super-exchange interactions in iron sulfide. M0.025Fe0.975S (MZSc, Ti, V, Cr, Mn, Co, Ni, Cu) samples were prepared by direct reaction of the elements (of high purity, better than 99.995%). Mixtures of the proper proportions of the elements sealed in evacuated quartz ampoules were heated to 600 8C for 1 day, to 1000 8C for 3 days, and then quenched down to room temperature. In order to obtain homogeneous material it was necessary grind the sample after the first firing and to press the powder into a pellet before annealing it for a
328
H.D. Nam et al. / Solid State Communications 135 (2005) 327–329
second time in an evacuated and sealed quartz ampoule. A third firing similar to the second one was required to get the single-phase samples. All the samples were 57Fe enriched to 5 at.% of the metal atoms for Mo¨ssbauer measurements. Mo¨ssbauer spectra were recorded using a conventional Mo¨ssbauer spectrometer of the electromechanical type with a 57Co source in a rhodium matrix. To produce a uniform thickness over the area of Mo¨ssbauer absorber, each sample was mixed with boron nitride powder and clamped between thin boron nitride plates. Examination of the samples by X-ray diffraction at room temperature showed that each sample crystallized in a single phase with a hexagonal structure. Table 1 shows the hexagonal lattice parameters ao and Co for various M0.025Fe0.975S. It is evident that there is no definite relationship between the lattice parameters and the number of 3d electrons. However, it is noteworthy that V0.025Fe0.975S and Co0.025Fe0.975S have lattice parameters which are distinctly different from those of FeS; furthermore, the directions of changes of the lattice parameters are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. ao of V0.025Fe0.975S is much less than that of FeS, while ao of Co0.025Fe0.975S is much larger than that of FeS. However, Co of V0.025Fe0.975S is larger than that of FeS whereas Co of Co0.025Fe0.975S is less than that of FeS. Mo¨ssbauer spectra of the M0.025Fe0.975S samples were taken at various temperatures ranging between liquid nitrogen temperature and 600 K. Using a least-squares computer program, one set or two of the six Lorentzian lines were fitted to the Mo¨ssbauer spectra below the Ne´el temperature. Ta was obtained from the temperature dependence of the magnetic hyperfine field Hhf for M0.025Fe0.975S in Mo¨ssbauer parameters. When the crystallographic phase transition appears, the magnetic hyperfine fields for the two phases have different values, respectively, at Ta. TM was got from the temperature dependence of the quadrupole splitting EQ for M0.025Fe0.975S in Mo¨ssbauer parameters. The quadrupole shift jumps abruptly from minus to plus value at about TM corresponding to a change Table 1 Lattice parameters of M0.025Fe0.975S (MZSc, Ti, V, Cr, Mn, Co, Ni, Cu) M(3dn) 1
Sc(3d ) Ti(3d2) V(3d3) Cr(3d4) Mn(3d5) Fe(3d6) Co(3d7) Ni(3d8) Cu(3d9) a
˚) ao (A 5.9702 5.9692 5.9462 5.9792 5.9672 5.9682 5.9912 5.9652 5.9882
˚) Co (A a
11.695 11.695 11.835 11.735 11.725 11.745 11.545 11.715 11.665
Subscript below each number indicates estimated error in the last digit.
Fig. 1. Compositional dependence of Ne´el temperature TN, a transition temperature Ta, and the Morin transition temperature TM.
in the spin-rotation with increasing temperature. It can be seen in Fig. 1 that both the Ne´el temperature TN and the a-transition temperature Ta are almost unaffected by the 3dtransition metal impurities. In another words, both the superexchange interaction and the superstructure transition are insensitive to the number of 3d electrons of the transitionmetal impurities. However, the spin-rotation transition is very sensitive to the kind of impurities as can be seen in Fig. 1. It is noteworthy that both V0.025Fe0.975S and Co0.025Fe0.975S have Morin transition temperatures TM which are distinctly different from that of FeS; furthermore, the directions of changes of TM are opposite for V0.025Fe0.975S and Co0.025Fe0.975S. TM of V0.025Fe0.975S is higher by 80 K than that of FeS while TM of Co0.025Fe0.975S is lower by 200 K than that of FeS. Comparison of the Morin transition temperatures with the lattice parameters for V0.025Fe0.975S and Co0.025Fe0.975S shows that there seems to be some correlation between the spin-rotation and the lattice parameters. It is very interesting that the crystallographic transition is independent of the lattice parameters while the spin-rotation transition is dependent on them. It is also noted that the crystallographic phase transition for V0.025Fe0.975S takes place a narrow temperature region of about 15 K more rapidly than that for other M0.025Fe 0.975S; furthermore, the a transition for V0.025Fe0.975S has a hysteresis [5] width of 4 K, whereas no hysteresis was observed for FeS. The sharpening of the crystallographic transition due to the vanadium impurities is in marked contrast to the broadening of the coexistence region by Co or Cr impurities.
Acknowledgements This research was supported by the Yeungnam University research grants in 2004.
H.D. Nam et al. / Solid State Communications 135 (2005) 327–329
References [1] F. Bertaut, Bull. Soc. Fr. Mineral. Crystallogr. 79 (1956) 276. [2] E. Hirahara, M. Murakami, J. Phys. Chem. Solids 7 (1958) 281. [3] J.T. Sparks, W. Mead, A.J. Kirschbaum, W. Marshall, J. Appl. Phys. 31 (1960) 356S. [4] A.F. Andresen, P. Torbo, Acta Chem. Scand. 21 (1967) 2841.
329
[5] R.C. Thiel, C.B. van den Berg, Phys. Status Solidi 29 (1968) 837. [6] J.T. Sparks, W. Mead, T. Komoto, J. Phys. Soc. Jpn. 17 (Suppl. B1) (1962) 249. [7] K.S. Baek, K.Y. Park, H.J. Kim, H.N. Ok, Phys. Rev. B 41 (1990) 9024. [8] H.N. Ok, K.S. Baek, H.J. Kim, J. Korean Phys. Soc. 25 (1992) 447.