phys. stat. sol. (c) 1, No. 7, 1660–1663 (2004) / DOI 10.1002/pssc.200304451

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Ferromagnetic behaviour in PrKMnMoO6 double perovskite oxide

S. Megdiche*, 1, M. Ellouze1, A. Cheikh-Rouhou1, and R. Madar2 1 Laboratoire de Physique des Matériaux, Faculté des Sciences de Sfax, B.P. 802, 3018 Sfax, Tunisie 2 Laboratoire des Matériaux et de Génie Physique, (UMR 5628 CNRS) ENSPG, B.P. 46, 38402 Saint

Martin d’Hères, France

Received 31 August 2003, accepted 31 December 2003 Published online 25 March 2004

PACS 71.30.+h, 75.60.Ef, 81.20.Ev

PrKMnMoO6 powder sample has been elaborated using the solid state technique at 1100 °C. Structural studies at room temperature show that our sample crystallizes in the orthorhombic structure with P222 space group. Magnetization measurements versus temperature of PrKMnMoO6 sample show a ferromag-netic behaviour at T ≤ 80 K. The critical exponent γ, defined by Msp = Msp(0) (1–(T/TC))γ and deduced from magnetization measurements versus magnetic applied field at several temperatures below TC, is found to be 0.31.

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

1 Introduction

A2FeMoO6 and A2FeReO6 (A = Ca, Sr, Ba) double perovskite compounds have attracted recent attention because they may be half metals with high magnetic transition temperatures and have spin-dependent transport properties which may be useful in magnetic devices [1–3]. These compounds were discovered in the 1960s [4–6], and are members of the broad class of A2B’B”O6 double perovskites [7]. More gen-erally, a survey of double perovskite A2B’B”O6 compounds shows that several of them are ferrimagnetic. Among them A2FeMoO6 (A = Ca, Sr, and Ba) are known to be ferrimagnetic with critical temperatures TC above room temperature [8]. Sr2MnMoO6 and Sr2CoMoO6 do not show any trace of ferromagnetic transition down to 5 K [9]. However LaKMnMoO6 exhibits a paramagnetic-ferromagnetic transition [10]. In this paper, we report the structural and magnetic properties of PrKMnMoO6 double perovskite oxide.

2 Experimental

Polycrystalline PrKMnMoO6 sample has been elaborated using the standard ceramic processing tech-nique by mixing Pr6O11, K2CO3, MnO2 and MoO3 up to 99.9% purity in the desired proportions accord-ing to the reaction

1/6 Pr6O11 + 0.5 K2CO3 + MnO2 + MoO3 → PrKMnMoO6 + δ CO2.

The precursors were mixed in an agate mortar and then sintered in air at about 950 °C for 72 hours with intermediate regrinding. A systematically annealing at high temperature is necessary to ensure a com-plete reaction. In fact the powder is pressed into pellets (of about 1mm thickness) and sintered at 1100 °C in air for 48 hours. Finally these pellets were rapidly quenched at room temperature in air. This step was

* Corresponding author: e-mail: smaiha@yahoo.fr, Phone: 00 216 74 274 923, Fax: 00 216 74 274 437

phys. stat. sol. (c) 1, No. 7 (2004) / www.pss-c.com 1661

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

done in order to retain the structure achieved at high temperature. In fact the magnetic properties depend strongly on the quenching method. Phase purity, homogeneity and cell dimensions were determined by powder X – ray diffraction at room temperature using a SIEMENS diffractometer with Fe radiation (λ = 1.936 Å). The cell parameters were obtained by least-squares calculations. Magnetization measurements versus temperature were recorded by a vibrating sample magnetometer in the temperature range 50–300 K in an applied field of 500 Oe. Magnetization measurements versus magnetic applied field up to 7 T at different temperatures has been preformed using an extraction magne-tometer.

3 Results and discussions

3.1 X-ray diffraction analysis

X-ray diffraction patterns at room temperature of PrKMnMoO6 sample are shown in Fig. 1. Our sample is single phase and no impurity was detected. PrKMnMoO6 sample crystallizes in the orthorhombic sys-tem with P222 space group, the same as LaKMnMoO6 [10]. The lattice parameters are found to be: a = 10.4155 Å, b = 9.8541 Å, c = 13.145 Å. The unit cell volume is equal to 1349.14 Å3. The unit cell vol-ume of LaKMnMoO6 is found to be V = 1360.32 Å [10], this result can be explained by the average ionic radius of La3+ which is larger than Pr3+ one (r[Pr3+] = 1.28 Å and r[La3+] = 1.32 Å) [11].

20 30 40 50 60 70 80

Inte

nsit

y (

a. u

.)

020

022

031

114

320

204

231

303

040 331

412

332

241

135

144

235

145

027

514

307

603162

444

213

Fig. 1 The X-ray diffraction patterns at room temperature for PrKMnMoO6 sample.

3.2 Magnetic properties

Figure 2 shows the temperature dependence of the magnetization for PrKMnMoO6 double perovskite oxide. Our sample exhibits an ordered state at low temperatures. The transition temperature is found to be 80 K. Previous study [10] showed that LaKMnMoO6 exhibits a paramagnetic to ferromagnetic transi-tion with decreasing temperature. The Curie temperature TC is found to be 180 K. This result can be probably explained by the average ionic radius of lanthanum which is larger than praseodymium one. It

2θ (°)

1662 S. Megdiche et al.: Ferromagnetic behaviour in PrKMnMoO6 double perovskite oxide

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

may be also explained by the praseodymium magnetic moment which leads to a weakness of the ferro-magnetic component. Our result may indicate that the Curie temperature TC depends strongly on the nature of the average ionic radius <rA> of the A cation site.

0.0

0.1

0.2

0.3

25 50 75 100 125 150

M (

em

u/g

)

T (K)

Fig. 2 Magnetization evolution versus temperature at 500 Oe for PrKMnMoO6 sample. In order to study the magnetic transition at low temperature, we performed magnetization measure-ments versus magnetic applied field up to 7 T at several temperatures for PrKMnMoO6 sample (Fig. 3).

0.0

0.5

1.0

1.5

2.0

2.5

0 1 2 3 4 5 6 7 8

300K

280K

260K

240K

240K

220K

200K

180K

150K

140K

120K

100K

80K

60K

40K

20K

10K

M (µB/m

ole

)

µ0H (Tesla)

Fig. 3 Magnetization evolution versus magnetic applied field at different temperatures for PrKMnMoO6 sample. Magnetization, at low temperatures (T < TC) increases sharply with magnetic applied field for H < 1 T but does not seem to saturate even for high magnetic applied field. Such result may indicate a spin canted state at low temperatures. The Curie temperature deduced from the Arrott curves (M2 versus H/M) [13] (Fig. 4) is found to be 80 K.

phys. stat. sol. (c) 1, No. 7 (2004) / www.pss-c.com 1663

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

0

1

2

3

4

5

6

0 2 4 6 8 10 12

10K

20K

40K

60K

80 K

100K

120K

140K

150K

M2 (µB/m

ole

)2

µ0H / M (Tesla/(µ

B/mole))

Fig. 4 Arrott curves for PrKMnMoO6 sample. The spontaneous magnetization of PrKMnMoO6 is found to be 1.29 Bµ /mole at 10 K. This value is

lower than that obtained in LaKMnMoO6 (3.25 Bµ /mole at 10 K). The critical exponent γ defined by

Msp = Msp (0) ( )C

C

T T

Tγ−

is equal to 0.31 for PrKMnMoO6 and 0.33 for LaKMnMoO6. The difference

may be explained by the praseodymium magnetic moment.

4 Conclusion

The structural and magnetic properties of PrKMnMoO6 double perovskite sample have been investi-gated. Our synthesized sample crystallizes in the orthorhombic system with P222 space group and exhib-its a paramagnetic to spin canted state transition with decreasing temperature. The transition temperature is found to be 80K, which is lower than that obtained in LaKMnMoO6. The critical exponent γ deduced from spontaneous magnetization versus temperature is found to be 0.31 for PrKMnMoO6.

Acknowledgements This study has been supported by the Tunisian Ministry of High Education, Scientific Re-search and Technology and by the CMCU collaboration (01 / F-1127).

References

[1] K. I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, and Y. Tokura, Nature 395, 677 (1998). [2] K. I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, and Y. Tokura, Phys. Rev B 59, 11159 (1999). [3] W. Prellier and V. Smolyaninova, J. Phys. C 12, 965 (2000). [4] F. K. Patterson, C. W. Moeller, and R. Wald, Inorg. Chem. 2, 196 (1963). [5] A. W. Sleigt and R. Ward, J. Am. Chem. Soc. 83, 1088 (1961). [6] T. Nakagawa, J. Phys. Soc. Jpn. 24, 806 (1968). [7] M. T. Anderson, K. B. Greenword, G. A. Taylor, and K. R. Peoppelmeier Prog. Solid State Chem. 22, 197

(1993). [8] F. Galasso, F. C. Douglas, and R. Kasper, J. Chem. Phys. 44, 1672 (1966). [9] Y. Moritomo, Sh. Xu, A. Machida, T. Akimoto, E. Nishibori, M. Takata, and M. Sakata, Phys. Rev. B 61, 7827

(2000). [10] S. Megdiche, M. Ellouze, A. Cheikh-rouhou, and R. Madar, J. Alloy. Comp. 347, 56 (2002). [11] R. D. Shannon, Acta crystal. B 25, 925 (1969). [12] A. W. Sleigt and J. F. Weiher, J. Phys. Chem. Solids 33, 679 (1972). [13] A. Arrott, Phys. Rev. 108, 1394 (1957).