Co-existence of giant magnetoresistance and large magnetocaloric effect near room temperature in nanocrystalline La 0.7 Te 0.3 MnO 3 Rabindra Nath Mahato n , K. Sethupathi, V. Sankaranarayanan, R. Nirmala Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India article info Article history: Received 29 January 2010 Received in revised form 22 March 2010 Available online 27 March 2010 Keywords: Oxide Magnetoresistance Magnetocaloric effect abstract Sol–gel prepared nanocrystalline La 0.7 Te 0.3 MnO 3 has rhombohedral crystal structure (space group R3 ¯ C) at room temperature and orders ferromagnetically at 280 K (T C ). A large magnetic entropy change of 12.5 J kg 1 K 1 is obtained near T C for a field change of 50 kOe. This magnetocaloric effect could be explained in terms of Landau theory. The temperature dependence of electrical resistivity shows metal– insulator transition at T C and a giant magnetoresistance of  52% in 50 kOe. The co-existence of giant magnetoresistance and large magnetocaloric effect near room temperature makes nanocrystalline La 0.7 Te 0.3 MnO 3 a promising material for magnetic refrigeration and spintronic device applications. & 2010 Elsevier B.V. All rights reserved. 1. Introduction Perovskite manganites with the general formula ABMnO 3 (where A ¼rare earth and B ¼alkaline-earth ions) have attracted a wide attention for their possible use in spintronic devices [1–4]. Currently, magnetocaloric effect (MCE) offers an alternate tech- nology for refrigeration, with enhanced efficiency and without environmental hazards [5,6]. As physicists strive hard to achieve room temperature magnetic refrigeration [7–10], it is of great importance to explore the compounds which exhibit large magnetic entropy changes for small applied fields near room temperature. It is also of equal importance to explore materials which show large magnetoresistance (MR) for spintronics devices [11,12]. MCE and MR in the perovskite oxides have been studied in the last ten years but the challenge to get suitable materials, which can be used at room temperature, still remains. Recently Patra et al. reported [13] on self doping La 1d MnO 3 (d ¼0.1), a maximum magnetic entropy change 4.9 J kg 1 K 1 for 20 kOe field change and MR  55% for a field change of 50 kOe at magnetic transition temperature of  254 K. In this self-doped material, La-deficiency leads to creation of Mn 4+ ions in the system that plays a key role in structural and transport properties. Aiming to obtain large MCE and MR around room temperature, we have doped Te at the La-site to enhance the T C , because tetravalent tellurium ion doping at La-site of LaMnO 3 system has led to observation of good colossal magnetoresistance (CMR) behavior in their bulk form [14,15]. Also, the decrease of grain size in La 0.9 Te 0.1 MnO 3 has been found to lead to an enhanced T C and to increase the magnetization values in the ferromagnetically ordered state and is attributed to the changes in Mn–O bond lengths and Mn–O–Mn bond angles [16]. This has motivated us to study Te-doped LaMnO 3 compound in its nanocrystalline form. In the present work, we study nanocrystalline La 0.7 Te 0.3 MnO 3 for their MR and MCE properties. Indeed we find large MCE coexisting with giant magnetoresistance in this compound close to room temperature. 2. Experimental details Nanocrystalline La 0.7 Te 0.3 MnO 3 compound was prepared by sol–gel method. Crystal structure and unit cell dimensions were determined by powder X-ray diffraction using Cu K a radiation (l ¼1.5405 ˚ A) at room temperature. The morphology, size and chemical composition of the samples were examined by scanning electron microscopy (SEM) attached with the energy dispersive X- ray analysis (EDAX) (FEI, Quanta-200) and high resolution transmission electron microscope. The magnetic measurements were performed using vibrating sample magnetometer (PPMS, Quantum Design) in the temperature range of 5–300 K. The electrical resistivity measurements were performed in the pre- sence of magnetic field using the conventional four probe method (PPMS, Quantum Design). The nanocrystalline powder has been compacted into a pellet for making electrical resistivity measure- ments. 3. Results and discussion The room temperature XRD data confirm single phase nature of the sample and the La 0.7 Te 0.3 MnO 3 compound has rhombohe- dral crystal structure with space group R3 ¯ C. The crystallite size of ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2010.03.015 n Corresponding author. E-mail address: rabindraiitm@gmail.com (R. Nath Mahato). Journal of Magnetism and Magnetic Materials 322 (2010) 2537–2540