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Magnetic properties of a cermet on the base of Al2O3
Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
Magnetic properties of a cermet on the base of Al O
C. Tien , E.V. Charnaya *, V.M. Gropyanov, I.S. Mikhailova, C.S. Wur , A.A. Abramovich Department of Physics, National Cheng Kung University, Tainan 701, Taiwan Institute of Physics, St. Petersburg State University, Petrodvorets, St. Petersburg 198904, Russia St. Petersburg State Technological University of Plant Polymers, St. Petersburg 198092, Russia Received 8 March 2000; received in revised form 23 June 2000
Abstract The zero-"eld-cooled and "eld-cooled magnetizations, magnetization versus "eld, and remanent magnetization were measured for a cermet on the base of Al O using a SQUID magnetometer in the temperature range of 2}360 K. It was shown that magnetic properties of the cermet are determined by independent ferromagnetic, paramagnetic and spin-glass contributions. The spin-glass behavior was studied. 2000 Elsevier Science B.V. All rights reserved. PACS: 81.05.M; 75.50.Lk; 75.30.Cr Keywords: Cermet; Magnetic properties; Spin glass; SQUIDS
Ceramic materials are used in various technical applications. Recently there has been an increasing interest in the metal}ceramic materials (cermets) on the base of oxides of metals such as Al O , ZrO , Y O sintered together with some metal or alloy powder because of their extreme strength and chemical and heat resistance [1}3]. In particular, cermets consisting of Al O grains with inclusions from refractory alloys can be utilized as an insert for rocket nozzles; as cores for regulation of the molten metal #ow; as #ame stabilizers in the combustion chamber of jet engines; as a material for the * Corresponding author. Institute of Physics, St. Petersburg State University, Tel.: #7-812-428-4330; fax: #7-812-4287240. E-mail address: [email protected], charnaya@ paloma.spbu.ru (E.V. Charnaya).
manufacture of bearings, and so on. While mechanical, thermal, and chemical properties of the cermets on the base of aluminum oxide are fairly well studied, their magnetic properties are very poorly known. It was assumed that magnetic features of the cermets are similar to those of the mix before sintering. However, the heat-treatment is known to change the chemical composition of starting compounds and then might in#uence the physical properties of cermets. In the present paper we report results of the "rst magnetic studies of a commonly employed cermet with the composition Al O -aus tenitic stainless-steel alloy. The measurements were carried out using a Quantum Design superconducting quantum interference device (SQUID) magnetometer with a 7T solenoid in the temperature range of 2}360 K. The zero-"eld-cooled (ZFC) and "eld-cooled (FC)
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 4 7 6 - 5
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C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
magnetization was measured at various magnetic "elds as well as the magnetization versus "eld dependences and the remanent magnetization. To avoid the in#uence of temperature overshoots near 4.2 K on the ZFC magnetization, we used a special program described in Ref. [4]. The cermet under study was obtained by pressing at room temperature and sintering at 1940 K in vacuum of the Al O powder with particle size ranging from 0.5 to 2.0 lm and steel powder of composition Fe Cr Ni Ti (stainless steel 12X18H10 T) formed as a result of aluminum oxide milling by steel balls. The average steel grain size after sintering was 1.4 lm, sizes of 75% of the grains ranged between 1.1 and 1.6 lm. The composition of the starting powder before pressing and sintering was 81% of Al O and 19% of steel. The micro structure of the cermet after sintering is shown in Fig. 1. The pores, steel inclusions, and Al O grains can be clearly seen. However, the X-ray powder di!raction pattern of the cermet shows, in addition to Al O and steel, the spectra corresponding to the spinel FeO(Cr O ,Al O ) and to a-Fe. These compounds were formed during sintering since their spectra did not appear in the X-ray powder di!raction pattern of the starting powder. The sample for magnetic studies has the form of a cylinder with a diameter of 3 mm and a length of 8 mm. Temperature dependences of the ZFC and FC magnetizations obtained in the magnetic "eld of 100 Oe are shown in Fig. 2. One can see from Fig. 2 that both ZFC and FC magnetizations are almost
independent of temperature above 50 K and near identical. The value of magnetization is rather small. Below 14 K the curves show a sharp breakaway. At lower temperatures the ZFC and FC magnetizations increase noticeably. The weak and temperature-independent magnetism above 50 K can be explained by the predominant contribution of a small amount of ferromagnetic a-Fe in the cermet. The increase in magnetization below 5 K obviously arises due to the paramagnetic contribution which stands out against the ferromagnetic background at low temperatures. The sharp breakaway of the ZFC and FC magnetizations near 14 K is similar to the magnetic behavior of spin glasses [5}7]. This became more clear when we subtracted the ferromagnetic and paramagnetic contributions from the ZFC and FC magnetizations (Fig. 3). The ferromagnetic contribution has been assumed to be temperature independent below 50 K and the usual 1/¹ dependence was used for the paramagnetic contribution. Thus, the temperature of the breakaway could be identi"ed with the temperature of spin freezing ¹ in the & magnetic "eld H"100 Oe [6]. Spin glass can be formed in the steel inclusions within the cermet sample. The possibility of the spin-glass formation
Fig. 1. Microstructure of the cermet under study. White, gray, and black sections are steel inclusions, aluminum oxide grains, and pores, respectively.
Fig. 2. Temperature dependence of magnetization for the cermet at a magnetic "eld of 100 Oe. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
Fig. 3. Temperature dependence of magnetization for the cermet at a magnetic "eld of 100 Oe after excluding the ferromagnetic and paramagnetic contributions as described in the text. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
in the Fe Cr Ni Ti steel was not studied, as far as we know. However, the spin-glass state was observed in some steels of similar composition (see Ref. [8], and references therein). Actually, our measurements on magnetization in the Fe Cr Ni Ti steel at 100 Oe revealed the spin-glass-like breakaway of the ZFC and FC magnetizations (Fig. 4). In contrast to the cermet, this breakaway occurred at about 43 K. The di!erence in freezing temperatures for the steel and the cermet might be a result of sintering which led to internal stresses and to some alterations in the alloy composition due to the formation of pure Fe and FeO(Cr O ,Al O ) solid solutions. To study the spin-glass-like behavior for the cermet in detail, we measured the ZFC and FC magnetizations at various magnetic "elds in the temperature range of 2}40 K. As an example, results for 10 and 1000 Oe are shown in Fig. 5. Similar dependences were obtained for other magnetic "elds in the range from 5 to 1000 Oe. One can see in Figs. 3 and 5 that the ZFC curve for small magnetic "elds exhibited a well-de"ned peak, but the peak broadened with increasing "eld and the breakaway of the ZFC and FC curves shifted to low temper-
149
Fig. 4. Temperature dependence of magnetization for the stainless steel 12X18H10 T at a magnetic "eld of 100 Oe. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
Fig. 5. Temperature dependence of magnetization for the cermet at a magnetic "eld of 10 Oe (circles) and of 1000 Oe (diamonds) measured in the temperature range of 2}40 K. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
atures. Such measurements allowed us to "nd the temperatures of the breakaway ¹ at di!erent & magnetic "elds with an accuracy better than 0.5 K. The dependence of ¹ on magnetic "eld can be &
150
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
Fig. 6. Temperature dependence of the remanent magnetization for the cermet.
Fig. 7. Magnetization versus magnetic "eld at 2 (open circles), 3.5 (closed circles), 10 (open diamonds), 13 (closed diamonds), 20 (open triangles), and 50 K (closed triangles) for the cermet.
well "tted by the relation ¹ !¹ JHa, (1) & where ¹ (the freezing temperature in zero "eld) is equal to 14.2 K and a"0.90$0.06. Relationship (1) is similar to that following from the mean-"eld theory [6], however, the exponent 0.90 di!ers from the mean-"eld prediction . The isothermal remanent magnetization was also measured as a magnetization in zero "eld after the application of a magnetic "eld of 7 T. First, the sample was cooled down to a target temperature in zero "eld, then the "eld was increased step by step until the upper limit and switched o!, the magnetization was measured in 30 s after stabilizing the "eld. The temperature dependence of the remanent magnetization is presented in Fig. 6. The increase of remanence with decreasing temperature below 14 K agrees with the suggestion about formation of spin glass in the cermet sample. One can see from Fig. 6 that the ferromagnetic contribution to the remanence is small. The magnetization versus magnetic "eld was measured for the cermet at several temperatures between 2 and 50 K. Results are shown in Fig. 7. For the temperature range under study, the saturation "eld was practically the same and equal to
Fig. 8. Magnetization at 2 (open circles), 3.5 (closed circles), 10 (open diamonds), 13 (closed diamonds), and 20 K (open triangles) minus magnetization at 50 K versus magnetic "eld divided by temperature for the cermet.
6500 Oe. Below the saturation "eld, the magnetization was a linear function of H and the magnetic susceptibility was equal to about 3.8;10\ emu/g. It was mainly related with ferromagnetic Fe inclusions since the paramagnetic and spin-glass
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
contributions are smaller in comparison (Fig. 2). Nevertheless, for low temperatures it was possible to separate these contributions by excluding the ferromagnetic magnetization. Assuming that the ferromagnetic contribution dominates at 50 K (see Fig. 2) and is temperature independent below this temperature, the other contributions can be calculated as the di!erence between the experimental magnetizations and the magnetization measured at 50 K. Results obtained in such a manner for several temperatures between 2 and 20 K are shown in Fig. 8 versus "eld divided by temperature. One can see from Fig. 8 that the magnetization curves calculated are superimposed for 10, 14, and 20 K as it should be in the case of paramagnetism while the curves for 2 and 3.5 K fall o! noticeably from them. This deviation agrees with the existence of the spin-glass state at low temperatures. In conclusion, magnetic studies of a cermet which was produced by sintering Al O and steel powders have shown that its magnetic properties are determined by ferromagnetic, paramagnetic, and spin-glass contributions, the former dominates above 50 K and the spin-glass has a freezing temperature near 14 K at zero "eld.
151
Acknowledgements The present work was supported by the National Science Council of Taiwan under Grant 89-2112-M-006-010 and by the Russian Foundation of Basic Researches under Grant 9902-16786. References [1] J.R. Tklepaugh, W.B. Crandall (Eds.), Cermets, Chapman and Hall, New York, 1960, p. 339. [2] A.P. Garshin, V.M. Gropyanov, G.P. Zaitsev, S.S. Semenov, Engineering Ceramics, St. Petersburg University, St. Petersburg, 1997, p. 726 (in Russian). [3] P.S. Kislyi et al. (Eds.), Cermets, Naukova Dumka, Kiev, 1985, p. 272 (in Russian). [4] E.V. Charnaya, C. Tien, K.J. Lin, C.S. Wur, Yu.A. Kumzerov, Phys. Rev. B 58 (1998) 467. [5] K. Binder, A.P. Young, Rev. Mod. Phys. 58 (1986) 801. [6] K.H. Fischer, J.A. Hertz, Spin Glasses, Cambridge University Press, Cambridge, UK, 1991. [7] M.J.P. Gingras, C.V. Stager, N.P. Raju, B.D. Gaulin, J.E. Greedan, Phys. Rev. Lett. 78 (1997) 947. [8] T.K. Nath, N. Sudhakar, E.J. McNi!, A.K. Majumdar, Phys. Rev. B 55 (1997) 12389.
Magnetic properties of a cermet on the base of Al O
C. Tien , E.V. Charnaya *, V.M. Gropyanov, I.S. Mikhailova, C.S. Wur , A.A. Abramovich Department of Physics, National Cheng Kung University, Tainan 701, Taiwan Institute of Physics, St. Petersburg State University, Petrodvorets, St. Petersburg 198904, Russia St. Petersburg State Technological University of Plant Polymers, St. Petersburg 198092, Russia Received 8 March 2000; received in revised form 23 June 2000
Abstract The zero-"eld-cooled and "eld-cooled magnetizations, magnetization versus "eld, and remanent magnetization were measured for a cermet on the base of Al O using a SQUID magnetometer in the temperature range of 2}360 K. It was shown that magnetic properties of the cermet are determined by independent ferromagnetic, paramagnetic and spin-glass contributions. The spin-glass behavior was studied. 2000 Elsevier Science B.V. All rights reserved. PACS: 81.05.M; 75.50.Lk; 75.30.Cr Keywords: Cermet; Magnetic properties; Spin glass; SQUIDS
Ceramic materials are used in various technical applications. Recently there has been an increasing interest in the metal}ceramic materials (cermets) on the base of oxides of metals such as Al O , ZrO , Y O sintered together with some metal or alloy powder because of their extreme strength and chemical and heat resistance [1}3]. In particular, cermets consisting of Al O grains with inclusions from refractory alloys can be utilized as an insert for rocket nozzles; as cores for regulation of the molten metal #ow; as #ame stabilizers in the combustion chamber of jet engines; as a material for the * Corresponding author. Institute of Physics, St. Petersburg State University, Tel.: #7-812-428-4330; fax: #7-812-4287240. E-mail address: [email protected], charnaya@ paloma.spbu.ru (E.V. Charnaya).
manufacture of bearings, and so on. While mechanical, thermal, and chemical properties of the cermets on the base of aluminum oxide are fairly well studied, their magnetic properties are very poorly known. It was assumed that magnetic features of the cermets are similar to those of the mix before sintering. However, the heat-treatment is known to change the chemical composition of starting compounds and then might in#uence the physical properties of cermets. In the present paper we report results of the "rst magnetic studies of a commonly employed cermet with the composition Al O -aus tenitic stainless-steel alloy. The measurements were carried out using a Quantum Design superconducting quantum interference device (SQUID) magnetometer with a 7T solenoid in the temperature range of 2}360 K. The zero-"eld-cooled (ZFC) and "eld-cooled (FC)
0304-8853/00/$ - see front matter 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 4 7 6 - 5
148
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
magnetization was measured at various magnetic "elds as well as the magnetization versus "eld dependences and the remanent magnetization. To avoid the in#uence of temperature overshoots near 4.2 K on the ZFC magnetization, we used a special program described in Ref. [4]. The cermet under study was obtained by pressing at room temperature and sintering at 1940 K in vacuum of the Al O powder with particle size ranging from 0.5 to 2.0 lm and steel powder of composition Fe Cr Ni Ti (stainless steel 12X18H10 T) formed as a result of aluminum oxide milling by steel balls. The average steel grain size after sintering was 1.4 lm, sizes of 75% of the grains ranged between 1.1 and 1.6 lm. The composition of the starting powder before pressing and sintering was 81% of Al O and 19% of steel. The micro structure of the cermet after sintering is shown in Fig. 1. The pores, steel inclusions, and Al O grains can be clearly seen. However, the X-ray powder di!raction pattern of the cermet shows, in addition to Al O and steel, the spectra corresponding to the spinel FeO(Cr O ,Al O ) and to a-Fe. These compounds were formed during sintering since their spectra did not appear in the X-ray powder di!raction pattern of the starting powder. The sample for magnetic studies has the form of a cylinder with a diameter of 3 mm and a length of 8 mm. Temperature dependences of the ZFC and FC magnetizations obtained in the magnetic "eld of 100 Oe are shown in Fig. 2. One can see from Fig. 2 that both ZFC and FC magnetizations are almost
independent of temperature above 50 K and near identical. The value of magnetization is rather small. Below 14 K the curves show a sharp breakaway. At lower temperatures the ZFC and FC magnetizations increase noticeably. The weak and temperature-independent magnetism above 50 K can be explained by the predominant contribution of a small amount of ferromagnetic a-Fe in the cermet. The increase in magnetization below 5 K obviously arises due to the paramagnetic contribution which stands out against the ferromagnetic background at low temperatures. The sharp breakaway of the ZFC and FC magnetizations near 14 K is similar to the magnetic behavior of spin glasses [5}7]. This became more clear when we subtracted the ferromagnetic and paramagnetic contributions from the ZFC and FC magnetizations (Fig. 3). The ferromagnetic contribution has been assumed to be temperature independent below 50 K and the usual 1/¹ dependence was used for the paramagnetic contribution. Thus, the temperature of the breakaway could be identi"ed with the temperature of spin freezing ¹ in the & magnetic "eld H"100 Oe [6]. Spin glass can be formed in the steel inclusions within the cermet sample. The possibility of the spin-glass formation
Fig. 1. Microstructure of the cermet under study. White, gray, and black sections are steel inclusions, aluminum oxide grains, and pores, respectively.
Fig. 2. Temperature dependence of magnetization for the cermet at a magnetic "eld of 100 Oe. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
Fig. 3. Temperature dependence of magnetization for the cermet at a magnetic "eld of 100 Oe after excluding the ferromagnetic and paramagnetic contributions as described in the text. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
in the Fe Cr Ni Ti steel was not studied, as far as we know. However, the spin-glass state was observed in some steels of similar composition (see Ref. [8], and references therein). Actually, our measurements on magnetization in the Fe Cr Ni Ti steel at 100 Oe revealed the spin-glass-like breakaway of the ZFC and FC magnetizations (Fig. 4). In contrast to the cermet, this breakaway occurred at about 43 K. The di!erence in freezing temperatures for the steel and the cermet might be a result of sintering which led to internal stresses and to some alterations in the alloy composition due to the formation of pure Fe and FeO(Cr O ,Al O ) solid solutions. To study the spin-glass-like behavior for the cermet in detail, we measured the ZFC and FC magnetizations at various magnetic "elds in the temperature range of 2}40 K. As an example, results for 10 and 1000 Oe are shown in Fig. 5. Similar dependences were obtained for other magnetic "elds in the range from 5 to 1000 Oe. One can see in Figs. 3 and 5 that the ZFC curve for small magnetic "elds exhibited a well-de"ned peak, but the peak broadened with increasing "eld and the breakaway of the ZFC and FC curves shifted to low temper-
149
Fig. 4. Temperature dependence of magnetization for the stainless steel 12X18H10 T at a magnetic "eld of 100 Oe. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
Fig. 5. Temperature dependence of magnetization for the cermet at a magnetic "eld of 10 Oe (circles) and of 1000 Oe (diamonds) measured in the temperature range of 2}40 K. Open symbols: FC magnetization; closed symbols: ZFC magnetization.
atures. Such measurements allowed us to "nd the temperatures of the breakaway ¹ at di!erent & magnetic "elds with an accuracy better than 0.5 K. The dependence of ¹ on magnetic "eld can be &
150
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
Fig. 6. Temperature dependence of the remanent magnetization for the cermet.
Fig. 7. Magnetization versus magnetic "eld at 2 (open circles), 3.5 (closed circles), 10 (open diamonds), 13 (closed diamonds), 20 (open triangles), and 50 K (closed triangles) for the cermet.
well "tted by the relation ¹ !¹ JHa, (1) & where ¹ (the freezing temperature in zero "eld) is equal to 14.2 K and a"0.90$0.06. Relationship (1) is similar to that following from the mean-"eld theory [6], however, the exponent 0.90 di!ers from the mean-"eld prediction . The isothermal remanent magnetization was also measured as a magnetization in zero "eld after the application of a magnetic "eld of 7 T. First, the sample was cooled down to a target temperature in zero "eld, then the "eld was increased step by step until the upper limit and switched o!, the magnetization was measured in 30 s after stabilizing the "eld. The temperature dependence of the remanent magnetization is presented in Fig. 6. The increase of remanence with decreasing temperature below 14 K agrees with the suggestion about formation of spin glass in the cermet sample. One can see from Fig. 6 that the ferromagnetic contribution to the remanence is small. The magnetization versus magnetic "eld was measured for the cermet at several temperatures between 2 and 50 K. Results are shown in Fig. 7. For the temperature range under study, the saturation "eld was practically the same and equal to
Fig. 8. Magnetization at 2 (open circles), 3.5 (closed circles), 10 (open diamonds), 13 (closed diamonds), and 20 K (open triangles) minus magnetization at 50 K versus magnetic "eld divided by temperature for the cermet.
6500 Oe. Below the saturation "eld, the magnetization was a linear function of H and the magnetic susceptibility was equal to about 3.8;10\ emu/g. It was mainly related with ferromagnetic Fe inclusions since the paramagnetic and spin-glass
C. Tien et al. / Journal of Magnetism and Magnetic Materials 220 (2000) 147}151
contributions are smaller in comparison (Fig. 2). Nevertheless, for low temperatures it was possible to separate these contributions by excluding the ferromagnetic magnetization. Assuming that the ferromagnetic contribution dominates at 50 K (see Fig. 2) and is temperature independent below this temperature, the other contributions can be calculated as the di!erence between the experimental magnetizations and the magnetization measured at 50 K. Results obtained in such a manner for several temperatures between 2 and 20 K are shown in Fig. 8 versus "eld divided by temperature. One can see from Fig. 8 that the magnetization curves calculated are superimposed for 10, 14, and 20 K as it should be in the case of paramagnetism while the curves for 2 and 3.5 K fall o! noticeably from them. This deviation agrees with the existence of the spin-glass state at low temperatures. In conclusion, magnetic studies of a cermet which was produced by sintering Al O and steel powders have shown that its magnetic properties are determined by ferromagnetic, paramagnetic, and spin-glass contributions, the former dominates above 50 K and the spin-glass has a freezing temperature near 14 K at zero "eld.
151
Acknowledgements The present work was supported by the National Science Council of Taiwan under Grant 89-2112-M-006-010 and by the Russian Foundation of Basic Researches under Grant 9902-16786. References [1] J.R. Tklepaugh, W.B. Crandall (Eds.), Cermets, Chapman and Hall, New York, 1960, p. 339. [2] A.P. Garshin, V.M. Gropyanov, G.P. Zaitsev, S.S. Semenov, Engineering Ceramics, St. Petersburg University, St. Petersburg, 1997, p. 726 (in Russian). [3] P.S. Kislyi et al. (Eds.), Cermets, Naukova Dumka, Kiev, 1985, p. 272 (in Russian). [4] E.V. Charnaya, C. Tien, K.J. Lin, C.S. Wur, Yu.A. Kumzerov, Phys. Rev. B 58 (1998) 467. [5] K. Binder, A.P. Young, Rev. Mod. Phys. 58 (1986) 801. [6] K.H. Fischer, J.A. Hertz, Spin Glasses, Cambridge University Press, Cambridge, UK, 1991. [7] M.J.P. Gingras, C.V. Stager, N.P. Raju, B.D. Gaulin, J.E. Greedan, Phys. Rev. Lett. 78 (1997) 947. [8] T.K. Nath, N. Sudhakar, E.J. McNi!, A.K. Majumdar, Phys. Rev. B 55 (1997) 12389.