Structural, magnetic and magnetocaloric properties of the compound La 0.94 Bi 0.06 MnO 3 T. Izgi, V.S. Kolat n , N. Bayri, H. Gencer, S. Atalay Inonu University, Science and Arts Faculty, Physics Department, 44280 Malatya, Turkey article info Article history: Received 5 May 2014 Received in revised form 26 June 2014 Available online 1 August 2014 Keywords: Perovskite-type La 1Àx Bi x MnO 3 Jahn–Teller effect Magnetocaloric effect abstract In this study, the magnetocaloric properties of lightly doped La 0.94 Bi 0.06 MnO 3 were investigated in detail. Polycrystalline manganite with the chemical composition La 0.94 Bi 0.06 MnO 3 was prepared by a standard solid-state process. An X-ray diffraction measurement indicated that the sample crystallised into a single phase, the orthorhombic structure. Magnetic measurements showed that relatively small amount of Bi doping in LaMnO 3 could cause ferromagnetic ordering. The Curie temperature was determined to be 209 K. The sample also exhibited a large magnetic entropy change |ΔS m | ¼1.58 J/kg K under a 1T magnetic field near the Curie temperature. Using the Landau theory and Arrott plots, the phase transition was determined to be first order. & 2014 Elsevier B.V. All rights reserved. 1. Introduction The study of perovskite manganites is undergoing intensive development, not only because these materials have considerable potential in technological applications related to the colossal magnetoresistance effect (CMR) [1] and the magnetocaloric effect (MCE) [2] but also because they have many fascinating magnetic and electronic properties. One of the most extensively studied systems is the La 1 Àx A x MnO 3 series of compounds, for which A constitutes divalent cations. It has been discovered that these systems have a rich variety of electronic and magnetic phases, such as ferromagnetic metal (FM-M), antiferromagnetic insulator (AFM-I), ferromagnetic insulator (FM-I), orbital order (OO) and charge order (CO) ground states [3,4]. The parent compound LaMnO 3 is an antiferromagnetic insula- tor. By substitution of divalent cations (A ¼ Ca 2 þ , Sr 2 þ , Ba 2 þ ) for La 3 þ , some of the Mn 3 þ ions are transformed into Mn 4 þ ions (which is called a mixed valence state), resulting in a transition from the antiferromagnetic insulating state to a ferromagnetic metallic state [5]. It is clear that using cations that have different ionic radii and oxidation states in such systems makes it possible to change the carrier density (Mn 3 þ /Mn 4 þ ) and the average ionic radii ( or A 4) of the A-sites, which control the Mn–O–Mn angle. The origin of ferromagnetism and antiferromagnetism, as well as the transport properties in these systems, has been explained well by a double-exchange (DE) interaction (between the Mn 3 þ and Mn 4 þ ions) and a super-exchange (SE) interaction (between the Mn 3 þ (4 þ ) and Mn 3 þ (4 þ) ions) [6]. However, the DE interactions promote FM spin ordering, and the SE interactions favour an AFM spin arrangement. The resultant magnetic and transport proper- ties of these systems are determined by a competition between the DE and SE interactions. Previous studies have shown that the strength of the DE and the SE interactions in doped manganites is very sensitive to variation in the Mn–O–Mn bond angle and the carrier concentration determined by the Mn 3 þ /Mn 4 þ ratio [7]. In recent studies, it has been shown that Bi 3 þ substitution for La 3 þ in manganites exhibits unusual magnetic and electrical properties compared to those of common compounds [8–16]. Whereas LaMnO 3 has antiferromagnetic ordering, BiMnO 3 is characterised by ferromagnetic ordering of the spin magnetic moment of the Mn 3 þ ions [17,18]. The Bi 3 þ ion has a similar ionic radius and the same oxidation state as La 3 þ . In this case, neither the average ionic radii (〈r A 〉) nor the charge balance (Mn 3 þ /Mn 4 þ ) is expected to vary. However, previous studies on Bi-doped manganites have revealed that these compounds have dissimilar magnetic and electrical properties. The interesting point here is the cause of this change in the magnetic and transport properties, despite the very similar ionic radii and oxidation states of the La 3 þ and Bi 3 þ ions. All the above mentioned properties make this compound very special compared to other manganites perovs- kites. Therefore, a large amount of work has already been performed on Bi-doped manganites [8–18]. Despite this, the results are contradictory. The fundamental magnetic characteris- tics of Bi-doped manganites have not been clarified yet. Although Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2014.07.037 0304-8853/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ90 4223773797; fax: þ90 4223410037. E-mail address: veli.kolat@inonu.edu.tr (V.S. Kolat). Journal of Magnetism and Magnetic Materials 372 (2014) 112–116