phys stat sol (b) 241, No 7, 1744 – 1747 (2004) / DOI 10.1002/pssb.200304587 Large magnetocaloric effect in La0.845Sr0.155Mn1–xMxO3 (M = Mn, Cu, Co) perovskites Manh-Huong Phan1, The-Long Phan2, Seong-Cho Yu*, 2, Nguyen Duc Tho3, and Nguyen Chau3 Department of Aerospace Engineering, Bristol University, Queen’s Building, University Walk, Bristol, BS8 1TR, UK Department of Physics, Chungbuk National University, Cheongju, 361-763, South Korea Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Vietnam Received 10 November 2003, revised March 2004, accepted March 2004 Published online May 2004 PACS 75.30.Sg, 75.47.Lx We present the results of an investigation on the magnetocaloric effect in the perovskites of La0.845Sr0.155Mn1–xMxO3 (M = Mn, Cu, Co) It is found that there was a large magnetic entropy change, i.e a large magneto-caloric effect, in all these samples Among them, the magnetic entropy change reaches a maximum value of 2.67 J/kg K at the applied field of 13.5 kOe for the Cu-doped sample, suggesting that this material would be a suitable candidate for the advanced magnetic refrigeration technology The large magnetic entropy change produced by the abrupt reduction of magnetization is attributed to the strong coupling between spin and lattice that occurs in the vicinity of the ferromagnetic-paramagnetic transition temperature (TC) – which is experimentally verified by electron paramagnetic resonance study © 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Introduction Recently, a large magnetocaloric (LMC) effect, which is defined as changes of the entropy related to the temperature change of a magnetic substance associated with an external magnetic field change in an adiabatic process, discovered in such perovskite manganites has attracted considerable interest in the science community, owing to its excellent potential for magnetic refrigeration applications [1 –4] Generally, there are two crucial factors for a magnetic material to possess a LMC One is a large enough spontaneous magnetization (belongs to a class of heavy rare-earth metals, for example, Gd metal) and the other is a sharp drop in magnetization with increasing temperature, associated with the ferromagnetic-paramagnetic transition at the Curie temperature (being found in such perovskite manganites) Apart from the above, it should be noted that most of the famous LMC materials were found to undergo a first-order magnetic transition (FOMT) [5, 6] As reported in Ref [6], the magnitude of the magnetic entropy change, ∆SM, around the first-order transition is about three times larger than that obtained around the second-order transition in the same compound of Nd0.5Sr0.5MnO3 The large entropy change in a FOMT originates from a difference in the degree of magnetic ordering between two adjacent magnetic phases The FOMT from a ferromagnetic state to paramagnetic one is therefore expected to show a LMC effect By far, Tian et al [7] have reported a larger magnetic entropy change in a La0.7Ca0.3MnO3 single crystal than in its polycrystalline material It is interesting to note that the ∆SM distribution in this single crystal has been found to be much more uniform than that of pure Gd metal and polycrystalline perovskite materials This feature is very desirable for an Ericson-cycle magnetic refrigerator Owing to its superior magnetocaloric properties, the lanthanum manganite single crystal is being expected to be one of the * Corresponding author: e-mail: scyu@chungbuk.ac.kr, Phone: +82 43 261 2269, Fax: 82 43 275 6416 © 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim phys stat sol (b) 241, No (2004) / www.pss-b.com 1745 most active magnetic refrigerants as working substances in magnetic refrigerators [8] Nevertheless, further efforts to search for poly-crystalline perovskite materials, which exhibit a larger magnetocaloric effect, have been devoted, because of the fact that polycrystalline manganese oxide samples are easy to be obtained by the conventional ceramic technique In this context, a detaied study of the magneto-caloric effect in the perovskites of La0.845Sr0.155Mn1–xMxO3 (M = Mn, Cu, Co) has been made Results show that the presently investigated samples could be suitable candidates as working materials in magnetic refrigerators Experiment Ceramic polycrystalline samples: La0.845Sr0.155MnO3 (sample No 1), La0.845Sr0.155Mn0.9Cu0.1O3 (sample No 2), and La0.845Sr0.155Mn0.98Co0.02O3 (sample No 3) were prepared by the conventional solid-state reaction technique using a stoichiometric mixture of 3N La2O3, SrCO3, MnCO3, CuO and CoO The samples were sintered at 1250 °C for 15 hours The quality of the samples was confirmed using a Bruker X-ray Diffractometer D5005 Results show that the three samples are of single phase with orthorhombic structure Magnetic measurements were carried out with a Vibrating Sample Magnetometer (VSM) DMS880 Digital Measurement Systems in the field up to 13.5 kOe Results and discussion As shown in Fig 1, temperature dependences of the magnetization of a representative sample of La0.845Sr0.155Mn0.9Cu0.1O3 (sample No 2) were measured in the fields of 50 Oe and 10 kOe (in the insert of Fig 1) The Curie temperature is ~265 K and ~267 K at H = 50 Oe and 10 kOe, respectively The ferromagnetic ordering transition temperature TC, defined as the temperature at which the ∂M/∂T – T curve reaches a minimum, has been determined from the M–T curves It is found that partial substitution of Mn by Cu or Co in the precursor of La0.845Sr0.155MnO3 (sample No 1) led to a slight decrease in TC but enhanced magnetization Interestingly, at H = 10 kOe the TC is shifted to a higher temperature (~267 K) meanwhile the shape of the M–T curve remains almost unchanged As reported earlier in Ref [9] on the other hand, the LMC material MnAs0.9Sb0.1 indicated smooth temperature variation of the magnetization under high fields whereas the shape of the M–T curve for MnAs was almost unchanged, except the increase of magnetization and the shift of TC towards higher temperature as usual Consequently, MnAs was found to exhibit a larger magneto-caloric effect than that in MnAs0.9Sb0.1 In the present case, a more abrupt jump in magnetization associated with the ferromagnetic to paramagnetic transition at TC is observed for the two Cu- and Co-doped samples (samples No and 3, respectively), as compared to sample No Therefore, samples No and would be expected to show a larger magnetic entropy change than that observed in sample No In Fig 2, the isothermal magnetization of sample No was measured with a field step of 500 Oe in the field range of – 13.5 kOe and a temperature step of K in the temperature range of 100 –300 K It is adequate to consider the magnetization curves to be isothermal for a sufficiently low sweeping rate of the magnetic field To ensure the readability of the figure, only several of them are presented in Fig Obviously, there shows a drastic 60 M (emu/g) H = 50 Oe H = 10 kOe 40 20 TC = 267 K 110 165 220 275 TC = 265 K 100 150 200 250 300 350 400 450 Fig Temperature dependence of the magnetization under magnetic fields of H = 50 Oe and 10 kOe (in the inset) for Sample No T (K) © 2004 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 1746 M.-H Phan et al.: Large magnetocaloric effect in La0.845Sr0.155Mn1–xMxO3 (M = Mn, Cu, Co) perovskites 3.0 70 220 K 230 K 240 K 245 K 250 K 255 K 260 K 265 K 270 K 280 K 300 K 50 40 30 20 10 DSM (J/kg K) M (emu/g) Sample No Sample No Sample No 2.5 60 2.0 1.5 1.0 0.5 0 12 16 H (kOe) Fig Isothermal magnetization for Sample No measured at different temperatures around TC 180 210 240 270 300 330 360 T (K) Fig Magnetic–entropy change plotted against temperature for the three samples, ∆H = 13.5 kOe change of the magnetization curves around the TC, indicating a large magnetic entropy change around the TC It is worth noting that the main part of changes of the magnetization curves occurs in a relative lowfield range (