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Physica B 327 (2003) 307–310 Structure and magnetic properties of Gd4(Mn0.05Sb0.95)3 Manh-Huong Phana, Nguyen Ngoc Chaub, Suhk Kun Oha,*, Seong-Cho Yua b a Department of Physics, Chungbuk National University, Cheongju 361-763, South Korea Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Viet Nam Abstract This work studies the structure and magnetic properties of Gd4(Mn0.05Sb0.95)3 with the aim to clarify the role played by the magnetic Mn atom Upon substitution of Mn for Sb in the parent Gd4Sb3 compound, it is found that the inverted Th3P4-like structure has been somewhat expanded The Curie temperature is increased while magnetic moment, measured in the field of 50 kOe at 200 K, is slightly reduced The ferromagnetic semiconductor, Gd4(Mn0.05Sb0.95)3, undergoes a ferromagnetic to paramagnetic transition at 270 K Observed anomalies occur in the magnetization vs temperature curves measured in a very low magnetic field They are attributed to magnetic inhomogeneities resulting from a structural modification in Gd4(Mn0.05Sb0.95)3 r 2002 Elsevier Science B.V All rights reserved PACS: 75.50.Pp; 75.30.Cr Keywords: Gd4(Mn0.05Sb0.95)3; Structure; Inhomogeneity; Magnetic phase transition Introduction Following the recent discovery of III–V-based diluted magnetic semiconductors, which can be prepared by molecular-beam epitaxy by substitution of Mn for Ga in GaAs, many interesting phenomena that are combinations of electrical, optical and magnetic properties are observed Of special interest is the possibility to incorporate magnetic effects in semiconductors to develop effects needed for devices applications [1–2] As reported in Ref [3], the Curie temperature of the diluted magnetic semiconductor (Ga,Mn)N can be tuned in the wide temperature range of 228–370 K by varying the Mn content It is noteworthy that, in the ferromagnetic semiconductors (Ga,Mn)N [3] and Ga0.98Mn0.02As [4], it cannot be shown which are the Mn atoms participating in the ferromagnetism and which are the paramagnetic Mn atoms This is thought to be attributed to magnetic inhomogeneity in the material, which is caused by the partial participation of Mn atoms in the ferromagnetic ordering [4] Thus, it is desirable to further clarify the role of Mn in magnetic semiconductors In the present work, the effects of Mn substitution for Sb on the magnetic and structural properties of Gd4(Mn0.05Sb0.95)3 were investigated Experimental *Corresponding author Tel.: +82-43-261-2270; fax: +8243-274-7811 E-mail address: skoh@chungbuk.ac.kr (S.K Oh) Gd4(Mn0.05Sb0.95)3 was prepared by arc-melting The alloy was annealed at 11001C The details 0921-4526/03/$ - see front matter r 2002 Elsevier Science B.V All rights reserved PII: S - ( ) 7 - 308 M.-H Phan et al / Physica B 327 (2003) 307–310 of the sample preparation will be reported elsewhere [5] Structural analyses were made based on the extended X-ray absorption fine structure (EXAFS) and X-ray diffraction EXAFS experiments were carried out at the 7C EC EXAFS beam line of the Pohang Light Source (PLS) in Korea The magnetization was measured in a Quantum Design MPMS-5 SQUID magnetometer from to 300 K in magnetic fields up to 50 kOe Measurements of the real and imaginary parts of the AC susceptibility were carried out from 70 to 300 K in a Lakeshore 7000 Susceptometer atomic radius of Mn in comparison with Sb is probably the origin of the increased lattice constant of Gd4(Mn0.05Sb0.95)3 with respect to the pure Gd4Sb3 compound In order to study the influence of Mn substitution in Gd4Sb3, we have studied the magnetic properties of both Gd4Sb3 and Gd4(Mn0.05Sb0.95)3 In Fig 1, the temperature dependence of the magnetization of both compounds is shown, measured in an applied field of 100 Oe from to 300 K For both Gd4Sb3 and Gd4(Mn0.05Sb0.95)3 samples, there is a prominent difference between the FC (field-cooled) and ZFC (zero-field-cooled) magnetization below TC ; indicative of magnetic frustration arising from the competition between ferromagnetic and antiferromagnetic interactions [10] Obviously, both Gd4Sb3 and Gd4(Mn0.05Sb0.95)3 are ferromagnetic in the whole temperature range below the Curie temperature The TC values were determined to be 259 and 270 K for Gd4Sb3 and Gd4(Mn0.05Sb0.95)3, respectively Substitution of Mn for Sb in the parent Gd4Sb3 compound not only increases the volume of the unit cell but also increases the TC : This is consistent with the result reported earlier by Holtzberg et al [7] The M vs T curve Gd4(Mn0.05Sb0.95)3 exhibits slightly anomalous behavior in the temperature region from 150 to 255 K suggesting some kind of phase transition To further clarify this situation, measurements of the real and imaginary parts of the AC susceptibility were performed As can be seen in Fig 2, the real (w0 ) and imaginary (w00 ) parts of the AC susceptibility of the sample reveal similar unusual behavior Since no anomalous behavior is found in the temperature dependence of the parent compound Gd4Sb3, the small anomalies in the M vs T curves of Gd4(Mn0.05Sb0.95)3 can safely Results and discussions Compared with the parent Gd4Sb3 compound [7–9], we found that the inverted Th3P4-like structure has been somewhat expanded and the lattice constant of Gd4(Mn0.05Sb0.95)3 was deter( For comparison, we have mined to be 9.402 A summarized in Table the lattice constants of Gd4Sb3 and Gd4(Mn0.05Sb0.95)3 from several different studies One can see that partial replacement of Sb by Mn in the parent Gd4Sb3 compound increases the volume of the unit cell Similar behavior was observed in Ga1ÀxMnxAs [6] and Gd4(SbxBi1Àx)3 [7] compounds As reported in Ref [7], in Gd4(SbxBi1Àx)3 compounds, as the doping concentration x is increased, the lattice ( for Gd4Bi3 to constant a0 decreases from 9.38 A ( for Gd4Sb3 Additionally, a the value 9.22 A decrease of the Curie temperature TC with increasing Sb content has been reported [7] The decrease of TC and a0 with increasing Sb content in Gd4(SbxBi1Àx)3 may be due to the smaller atomic radius of Sb compared to Bi The larger Table Lattice constant a0 ; the magnetization M50 kOe ; measured in 50 kOe at 200 K and the Curie temperature TC for Gd4Sb3 and Gd4(Mn0.05Sb0.95)3 Composition Gd4Sb3 Gd4(Mn0.05Sb0.95)3 ( a0 (A) 9.224 9.224(5) 9.228–9.232 9.223(4) 9.402 M50 kOe (emu/g) 96 94.1 TC (K) Ref 260 [7] [8] [9] This work This work 259 270 M.-H Phan et al / Physica B 327 (2003) 307–310 H = 100 Oe Gd4Sb3 TC= 259 K ZFC FC 50 100 150 200 250 300 T (K) H = 100 Oe M (emu/g) be attributed to the presence of Mn in this sample The presence of very small amount of about 0.14% Mn (confirmed by EXAFS analysis) causes a structural modification in the sample, which in turn causes magnetic inhomogeneities They may be the origin of the anomalous behavior of the magnetization in the temperature region from 150 to 255 K, before the onset of ferromagneticparamagnetic phase transition The value of magnetic moment of Gd4(Mn0.05Sb0.95)3, measured in the field of 50 kOe at 200 K, is only slightly a bit smaller than that of Gd4Sb3 (Fig 3), but the presence of Mn in Gd4Sb3 causes the material to exhibit much softer ferromagnetic behavior (Fig 1) A similar effect has been reported for Gd4(SbxBi1Àx)3 compounds by doping with Bi [7] Gd4(Mn0.05Sb0.95)3 ZFC FC 0 50 100 TC= 270 K 100 150 T (K) 200 250 80 300 M (emu/g) M (emu/g) 309 Fig Temperature dependence of the magnetization at 100 Oe for both zero-field-cooled (ZFC) and field-cooled (FC) Gd4Sb3 (top panel) and Gd4(Mn0.05Sb0.95)3 (bottom panel) Gd4Sb3 60 T = 200 K 40 20 0.7 10000 20000 30000 40000 50000 60000 H (Oe) 0.6 100 Gd4(Mn0.05Sb0.95)3 80 0.2 0.1 χ (arb units ) 0.3 0.012 0.008 M (emu/g) 0.016 0.4 , χ (arb units) 0.5 HAC = 10 Oe f = 80 Hz T = 200 K 40 0.004 0.000 50 20 100 150 200 250 300 T (K) 0.0 50 Ga4(Mn0.05Sb0.95)3 60 100 150 200 250 300 Temperature (K) Fig Temperature dependence of the real (w0 ) and imaginary (w00 ) parts of the AC susceptibility of Gd4(Mn0.05Sb0.95)3 10000 20000 30000 40000 50000 60000 H (Oe) Fig Magnetic-field dependence of the magnetization at 200 K for both Gd4Sb3 (top panel) and Gd4(Mn0.05Sb0.95)3 (bottom panel) M.-H Phan et al / Physica B 327 (2003) 307–310 310 M (emu/g) 150 10 K 100 K 160 K 200 K 220 K 240 K 260 K 265 K 270 K 275 K 280 K 285 K 290 K 300 K 100 50 0 10000 20000 30000 40000 50000 60000 magnetic behavior The ferromagnetic semiconundergoes the ductor, Gd4(Mn0.05Sb0.95)3 ferromagnetic to paramagnetic transition at 270 K The observed anomalies in the magnetization vs temperature curves, measured in a very low magnetic field, are likely to be attributed to magnetic inhomogeneities resulting from a structural modification in Gd4(Mn0.05Sb0.95)3 Acknowledgements H (Oe) Fig Magnetization vs field for Gd4(Mn0.05Sb0.95)3 at various temperatures in fields up to 50 kOe The temperatures of the isotherms are indicated In order to further elucidate the nature of the magnetic transition, magnetization vs magnetic field isotherms of Gd4(Mn0.05Sb0.95)3 were measured in the vicinity of TC : As can be seen in Fig 4, the M2H curves show a normal monotonic decrease of the magnetization with increasing temperature This might be due to a monotonic phase transition and a weak coupling between spin and lattice in the magnetic ordering process arising from inhomogeneity in the sample [11] Similar behavior has also been observed for the parent compound Gd4Sb3 [7] Conclusions The structural and magnetic properties of Gd4(Mn0.05Sb0.95)3 were investigated The partial replacement of Sb by Mn in the parent compound Gd4Sb3 causes an expansion of the inverted Th3P4like structure and an increase of the Curie temperature of about 10 K The presence of Mn in Gd4Sb3 causes a small anomaly in the ferro- This work was supported by the Korea Research Foundation Grant (KRF-2001-005D20010) References [1] A Oiwa, S Katsumoto, A Endo, M Hirasawa, Y Iye, H Ohno, F Matsukura, A Shen, Y Sugawara, Solid State Commun 103 (1997) 209 [2] F Matsukara, H Ohno, A Shen, Y Sugawara, Phys Rev B 57 (1998) R2037 [3] M.L Reed, N.A El-Masry, H.H Stadelmaier, M.K Ritums, M.J Reed, C.A Parker, J.C Roberts, S.M Bedair, Appl Phys Lett 79 (2001) 3473 [4] H Ohldag, V Sonilus, F.U Hillebrecht, J.B Goedkoop, M Finazzi, F Matsukura, H Ohno, Appl Phys Lett 76 (2001) 2928 [5] Nguyen Ngoc Chau, Manh-Huong Phan, to be published [6] S.J Potashnik, K.C Ku, S.H Chun, J.J Berry, N Samarth, P Schiffer, Appl Phys Lett 79 (2001) 1495 [7] F Holtzberg, T.R McGuire, S Methfessel, J.C Suits, J Appl Phys 35 (1964) 1033 [8] R.J Gambino, J Less-Common Metals 12 (1967) 344 [9] G Borzone, M.L Fornasini, N Parodi, R Ferro, Intermetallics (2000) 189 [10] J.G Park, M.S Kim, H.C Ri, K.H Kim, T.W Noh, S.W Cheong, Phys Rev B 60 (1999) 14804 [11] S.E Lofland, K.V Ramanujachary, W.H McCarroll, J Magn Magn Mater 238 (2002) 22 ... Gd4(Mn0.05Sb0.95)3 at various temperatures in fields up to 50 kOe The temperatures of the isotherms are indicated In order to further elucidate the nature of the magnetic transition, magnetization vs magnetic. .. value of magnetic moment of Gd4(Mn0.05Sb0.95)3, measured in the field of 50 kOe at 200 K, is only slightly a bit smaller than that of Gd4Sb3 (Fig 3), but the presence of Mn in Gd4Sb3 causes the material... the FC (field-cooled) and ZFC (zero-field-cooled) magnetization below TC ; indicative of magnetic frustration arising from the competition between ferromagnetic and antiferromagnetic interactions
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