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Colossal magnetoresistance of perovskite Nd0.67Sr0.33Mn1−xFexO3 single crystals
Journal of Magnetism and Magnetic Materials 226}230 (2001) 884}885
Colossal magnetoresistance of perovskite Nd Sr Mn Fe O single crystals \V V Jun Takeuchi*, Seitaro Hirahara, Tara P. Dhakal, Kiyotaka Miyoshi, Kenji Fujiwara Department of Material Science, Shimane University, Matsue 690-8504, Japan
Abstract The e!ect of Fe doping on the Mn site in the ferromagnetic phases of the perovskite Nd Sr Mn Fe O single \V V crystals grown by the #oating zone method has been studied. Conduction and ferromagnetism are suppressed by Fe doping. The material with x"0.1 shows a cluster glass-like behavior with spin freezing temperature ¹ "70 K instead of a long-range ferromagnetic order for mother material (x"0) with ¹ "240 K. The resistivity for x"0.1 has a very large peak near ¹ , where a metal}insulator transition takes place. Besides, the magnetic "eld causes the colossal magnetoresistance near ¹ . The "eld of 7 T suppresses the resistivity by an order of magnitude 3 for x"0.1 single crystal, which is to be compared with reduction of an order of magnitude 1.5 for the sister material, and much larger than the suppression of resistivity near ¹ for x"0 single crystal. Further doped material with x"0.2 shows the spin-glass-like and insulating behaviors with rather small magnetoresistance. These results are ascribed to the frustration of random competing ferromagnetic and antiferromagnetic interactions with the introduction of Fe> ions, which do not participate in the double-exchange process. 2001 Elsevier Science B.V. All rights reserved. Keywords: Magnetoresistance*giant; Spin glass*behavior; Phase transitions* metal}insulator; Doping e!ects
There has been renewed interest in physical properties of hole-doped perovskite manganites La Sr MnO , \V V since these materials show exotic electronic transport and magnetic properties and colossal magnetoresistance (CMR) (for a review, see Ref. [1]). Double-exchange (DE) interactions between Mn>/Mn> pairs and the lattice distortion are believed to play an important role in the properties of these materials. Though many works have been done through doping of the La sites, far fewer studies have been made in doping Mn sites, which are at the heart of the DE [2}4]. Further, these fewer studies have been done on sintered polycrystals, where the transport properties at low temperatures might have been a!ected by grain boundaries. In this work, we have undertaken a study of the e!ect of Fe doping on the Mn site in Nd Sr Mn Fe O single crystals. Single \V V
* Corresponding author. Fax: #81-852-32-6409. E-mail address: [email protected] (J. Takeuchi).
crystals with x"0, 0.1 and 0.2 were successfully grown by the #oating zone furnace with four pairs of ellipsoidal mirror and halogen lumps. The magnetization was measured by using a SQUID magnetometer. The resistivity with magnetic "eld up to 7 T was measured with the standard four-probe method. The temperature dependence of the magnetization for Nd Sr Mn Fe O at a "eld of 0.1 T is shown in \V V Fig. 1. The material with x"0.1 shows a cluster glasslike behavior with spin freezing temperature ¹ "70 K, below which there is a large di!erence between the "eldcooled (FC) and zero-"eld-cooled (ZFC) magnetization in contrast to a long-range ferromagnetic order for mother material (x"0) with ¹ "240 K. Further doped material with x"0.2 has greatly suppressed magnetization (data values in Fig. 1 for x"0.2 are magni"ed 5 times) and shows a spin glass-like behavior. The temperature dependence of the resistivity for Nd Sr Mn Fe O is shown in Fig. 2. The resis \V V tivity for x"0 shows a metallic behavior in the whole temperature region below ¹ . The resistivity for x"0.1
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 6 3 7 - 5
J. Takeuchi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 884}885
Fig. 1. Temperature dependence of the magnetization for Nd Sr Mn Fe O at a "eld of 0.1 T. \V V
Fig. 2. Temperature dependence Nd Sr Mn Fe O . \V V
of
the
resistivity
for
increases as temperature decreases, especially increasing steeply below 100 K, where the magnetization increases largely, and reaches maximum near ¹ , and then de creases as temperature decreases further showing a metallic behavior. It is noticeable that the magnetic "eld causes the colossal magnetoresistance near ¹ . The "eld of 7 T suppresses the resistivity by an order of magnitude 3 for x"0.1 single crystal, which is to be compared with reduction of an order of magnitude 1.5 for the sister material [4], and much larger than the suppression of resistivity near ¹ for mother (x"0) single crystal. Fur ther doped material with x"0.2 shows an insulating behavior with rather small magnetoresistance. The value of resistivity at 50 K for x"0.2 is over 8 orders of magnitude higher than that for x"0. The magnetic "eld dependence of the resistivity for Nd Sr Mn Fe O is shown in Fig. 3. Data are taken after zero-"eld cooling from room temperature to each measured temperature. As can be seen, there exists very large hysteresis. The resistivity at ¹"10 K once
885
Fig. 3. Magnetic "eld dependence of the resistivity for Nd Sr Mn Fe O .
decreased by 3 order of magnitude by the applying 7 T "eld recovers only 1% and keeps small value by 2 order of magnitude when H is decreased to zero again. The resistivity at ¹"60 K recovers 90% in the same process. The large hysteresis in isothermal magnetoresistance as well as the di!erence between FC and ZFC magnetization for x"0.1 material supports that this material is in a cluster-like state below ¹ , which could explain the appearance of CMR of this material. An external magnetic "eld tends to align the spins of ferromagnetic clusters and enhance the double-exchange interaction, thus giving rise to the CMR. The appearance of this cluster glass-like behaviors can be ascribed to the frustration of random competing ferromagnetic and antiferromagnetic interactions with the introduction of Fe> ions, which do not participate in the double-exchange process. As Fe doping becomes higher, the ferromagnetic coupling between Mn ions becomes weaker. The material with x"0.2 would be in a spin-glass-like state with no appreciable number of clusters and will not exhibit large CMR.
References [1] C.N.R. Rao, B. Raveau (Eds.), Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides, World Scienti"c, Singapore, 1998. [2] K.H. Ahn, X.W. Wu, K. Liu, C.L. Chien, Phys. Rev. B 54 (1996) 15299. [3] N. Gayathri, A.K. Raychaudhuri, S.K. Tiwary, R. Gundakaram, A. Arulraj, C.N.R. Rao, Phys. Rev. B 56 (1997) 1345. [4] J. Takeuchi, A. Uemura, K. Miyoshi, K. Fujiwara, Physica B 284}288 (2000) 1444.
Colossal magnetoresistance of perovskite Nd Sr Mn Fe O single crystals \V V Jun Takeuchi*, Seitaro Hirahara, Tara P. Dhakal, Kiyotaka Miyoshi, Kenji Fujiwara Department of Material Science, Shimane University, Matsue 690-8504, Japan
Abstract The e!ect of Fe doping on the Mn site in the ferromagnetic phases of the perovskite Nd Sr Mn Fe O single \V V crystals grown by the #oating zone method has been studied. Conduction and ferromagnetism are suppressed by Fe doping. The material with x"0.1 shows a cluster glass-like behavior with spin freezing temperature ¹ "70 K instead of a long-range ferromagnetic order for mother material (x"0) with ¹ "240 K. The resistivity for x"0.1 has a very large peak near ¹ , where a metal}insulator transition takes place. Besides, the magnetic "eld causes the colossal magnetoresistance near ¹ . The "eld of 7 T suppresses the resistivity by an order of magnitude 3 for x"0.1 single crystal, which is to be compared with reduction of an order of magnitude 1.5 for the sister material, and much larger than the suppression of resistivity near ¹ for x"0 single crystal. Further doped material with x"0.2 shows the spin-glass-like and insulating behaviors with rather small magnetoresistance. These results are ascribed to the frustration of random competing ferromagnetic and antiferromagnetic interactions with the introduction of Fe> ions, which do not participate in the double-exchange process. 2001 Elsevier Science B.V. All rights reserved. Keywords: Magnetoresistance*giant; Spin glass*behavior; Phase transitions* metal}insulator; Doping e!ects
There has been renewed interest in physical properties of hole-doped perovskite manganites La Sr MnO , \V V since these materials show exotic electronic transport and magnetic properties and colossal magnetoresistance (CMR) (for a review, see Ref. [1]). Double-exchange (DE) interactions between Mn>/Mn> pairs and the lattice distortion are believed to play an important role in the properties of these materials. Though many works have been done through doping of the La sites, far fewer studies have been made in doping Mn sites, which are at the heart of the DE [2}4]. Further, these fewer studies have been done on sintered polycrystals, where the transport properties at low temperatures might have been a!ected by grain boundaries. In this work, we have undertaken a study of the e!ect of Fe doping on the Mn site in Nd Sr Mn Fe O single crystals. Single \V V
* Corresponding author. Fax: #81-852-32-6409. E-mail address: [email protected] (J. Takeuchi).
crystals with x"0, 0.1 and 0.2 were successfully grown by the #oating zone furnace with four pairs of ellipsoidal mirror and halogen lumps. The magnetization was measured by using a SQUID magnetometer. The resistivity with magnetic "eld up to 7 T was measured with the standard four-probe method. The temperature dependence of the magnetization for Nd Sr Mn Fe O at a "eld of 0.1 T is shown in \V V Fig. 1. The material with x"0.1 shows a cluster glasslike behavior with spin freezing temperature ¹ "70 K, below which there is a large di!erence between the "eldcooled (FC) and zero-"eld-cooled (ZFC) magnetization in contrast to a long-range ferromagnetic order for mother material (x"0) with ¹ "240 K. Further doped material with x"0.2 has greatly suppressed magnetization (data values in Fig. 1 for x"0.2 are magni"ed 5 times) and shows a spin glass-like behavior. The temperature dependence of the resistivity for Nd Sr Mn Fe O is shown in Fig. 2. The resis \V V tivity for x"0 shows a metallic behavior in the whole temperature region below ¹ . The resistivity for x"0.1
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 6 3 7 - 5
J. Takeuchi et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 884}885
Fig. 1. Temperature dependence of the magnetization for Nd Sr Mn Fe O at a "eld of 0.1 T. \V V
Fig. 2. Temperature dependence Nd Sr Mn Fe O . \V V
of
the
resistivity
for
increases as temperature decreases, especially increasing steeply below 100 K, where the magnetization increases largely, and reaches maximum near ¹ , and then de creases as temperature decreases further showing a metallic behavior. It is noticeable that the magnetic "eld causes the colossal magnetoresistance near ¹ . The "eld of 7 T suppresses the resistivity by an order of magnitude 3 for x"0.1 single crystal, which is to be compared with reduction of an order of magnitude 1.5 for the sister material [4], and much larger than the suppression of resistivity near ¹ for mother (x"0) single crystal. Fur ther doped material with x"0.2 shows an insulating behavior with rather small magnetoresistance. The value of resistivity at 50 K for x"0.2 is over 8 orders of magnitude higher than that for x"0. The magnetic "eld dependence of the resistivity for Nd Sr Mn Fe O is shown in Fig. 3. Data are taken after zero-"eld cooling from room temperature to each measured temperature. As can be seen, there exists very large hysteresis. The resistivity at ¹"10 K once
885
Fig. 3. Magnetic "eld dependence of the resistivity for Nd Sr Mn Fe O .
decreased by 3 order of magnitude by the applying 7 T "eld recovers only 1% and keeps small value by 2 order of magnitude when H is decreased to zero again. The resistivity at ¹"60 K recovers 90% in the same process. The large hysteresis in isothermal magnetoresistance as well as the di!erence between FC and ZFC magnetization for x"0.1 material supports that this material is in a cluster-like state below ¹ , which could explain the appearance of CMR of this material. An external magnetic "eld tends to align the spins of ferromagnetic clusters and enhance the double-exchange interaction, thus giving rise to the CMR. The appearance of this cluster glass-like behaviors can be ascribed to the frustration of random competing ferromagnetic and antiferromagnetic interactions with the introduction of Fe> ions, which do not participate in the double-exchange process. As Fe doping becomes higher, the ferromagnetic coupling between Mn ions becomes weaker. The material with x"0.2 would be in a spin-glass-like state with no appreciable number of clusters and will not exhibit large CMR.
References [1] C.N.R. Rao, B. Raveau (Eds.), Colossal Magnetoresistance, Charge Ordering and Related Properties of Manganese Oxides, World Scienti"c, Singapore, 1998. [2] K.H. Ahn, X.W. Wu, K. Liu, C.L. Chien, Phys. Rev. B 54 (1996) 15299. [3] N. Gayathri, A.K. Raychaudhuri, S.K. Tiwary, R. Gundakaram, A. Arulraj, C.N.R. Rao, Phys. Rev. B 56 (1997) 1345. [4] J. Takeuchi, A. Uemura, K. Miyoshi, K. Fujiwara, Physica B 284}288 (2000) 1444.