Room temperature magnetic entropy change and magnetoresistance in La0.70(Ca0.30−xSrx)MnO3:Ag 10% (x=0.0−0.10)

Abstract

The magnetic and magnetocaloric properties of polycrystalline La 0.70 x Sr x )MnO 3 :Ag 10% manganite have been investigated. All the compositions are crystallized in single phase orthorhombic Pbnm space group. Both, the Insulator-Metal transition temperature (T IM ) and Curie temperature (T c ) are observed at 298 K for x = 0.10 composition. Though both T IM and T c are nearly unchanged with Ag addition, the MR is slightly improved. The MR at 300K is found to be as large as 31% with magnetic field change of 1Tesla, whereas it reaches up to 49% at magnetic field of 3Tesla for La 0.70 Ca 0.20 Sr 0.10 MnO 3 :Ag 0.10 sample. The maximum entropy change (∆S Mmax ) is 7.6 J.Kg -1 .K -1 upon the magnetic field change of 5Tesla, near its T c (300.5 K). IntroductionManganites are considered to be promising candidate for the technological applications such as bolometer and magnetic refrigeration [1][2][3][4][5][6][7]. Along with the all other fascinating properties, the presence of magnetocaloric nature makes them more outstanding material. Practically one desires to have higher Temperature coefficient of resistance (TCR), MR and magnetic entropy change near room temperature i.e. at around 300 K. It is seen that the maximum MR as well as TCR in hole-doped manganites occur near the insulator-metal (IM) transition T IM being accompanied with ferromagnetic (FM)-paramagnetic (PM) transition (Curie Temperature T c ).The steep transition about IM crossover determines the sensitivity as well as active zone for these sensors. Since magnetic refrigeration has a lot of advantages over gas refrigeration, manganites have been getting attention [4,[6][7]. Also, since the magnetic properties of perovskite 2 manganites, Curie temperature and saturation magnetization, are strongly doping-dependent, these typical materials are believed to be good candidates for magnetic refrigeration at various temperatures [5][6][7][8][9][10][11]. The magnetocaloric effect (MCE) is an isothermal magnetic entropy change or an adiabatic temperature change (∆T ad ) of a magnetic material caused by an applied magnetic field. The adiabatic temperature change ∆T ad is mainly affected by the magnetic entropy change |∆S M | [12]. The magnetic entropy change |∆S M | induced by a magnetic field change is another important parameter to describe the magnetocaloric effect. A constant magnetic entropy change over the working temperature range is required in an ideal Ericsson refrigeration cycle [13]. It has been observed that heavy rare-earth and their compounds are good candidates for finding a large MCE, due to their large magnetic moments [14,15]. The highest MCE involving a secondorder transition is found in gadolinium, which can be used to achieve cooling between 270 and 310 K [14]. However, the cost of a magnetic refrigerant using gadolinium is quite expensive, which limits the usage of it as an active magnetic refrigerant (AMR) in magnetic refrigerators. Further efforts to investigate new materials exhibiting large MCE in relatively low applied field a...

Investigation of the critical behavior in Mn0.94Nb0.06CoGe alloy by using the field dependence of magnetic entropy change

“…Typical representative materials include Gd 5 (Si 1Àx Ge x ) 4 7 and Ni-Mn-Ga. 8 Perovskite manganites are also considered to be promising candidate for the magnetic refrigeration. [9][10][11] Since the magnetic properties of perovskite manganites, Curie temperature and saturation magnetization, are strongly doping-dependent, these typical materials are believed to be good candidates for magnetic refrigeration at various temperatures. 12,13 However, for different reasons, none of these materials have yet been employed in a commercial refrigerator.…”

Observance of Improved Magneto-resistance and Magnetic Entropy Change in La0.7(Ca0.2Sr0.1)MnO3:Pd Composite

“…Considerable improvement in both the magnetic (MR) and magneto-caloric (MCE) properties of the pristine La 0.7 (Ca 0.2 Sr 0.1 )MnO 3 (LCSMO) has been observed with PdO addition. The maximum MR of 12.9 % (1 T) and 19.6 % (2 T) has been observed close to its T c (309 K) in the pristine LCSMO which The maximum values of magnetic entropy change | S M | of 11.7 J kg −1 K −1 (H = 3 T), 8.2 J kg −1 K −1 (H = 2 T) and 4.4 J kg −1 K −1 (H = 1 T) for LCSMO:Pd10 are found to be much higher than in the LCSMO single crystal and the corresponding LCSMO:Ag composite reported earlier [10,15]. LCSMO:Pd composite material possessing a sizable MR and high magnetic entropy value therefore shows an excellent possibility of a potential magnetic sensor and magnetic refrigerant close to room temperature.…”

“…The temperature dependence of the magnetic entropy change is shown in Fig. 7 [5,10,15]. These low field entropy values are also much higher when compared to manganites reported in the literature [5,14,16].…”

“…Efforts are being carried out to obtain sizable MR values at low fields (LFMR) and near room temperature [8,9]. Several manganite materials like LCBMO, LCSMO, PBMO and their composites with Ag 2 O and PdO have been investigated to explore their potential for magnetic sensing applications [8][9][10][11][12][13]. Besides, manganites have also shown good potential as active magnetic refrigerant (AMR) near room temperature [10,[14][15][16][17].…”

“…Thus we can expect to obtain enhanced properties in the composite material. Various manganite composites have been investigated for their efficacy towards magnetic sensing and refrigeration applications [8][9][10][11][12][13][14][15][16][17] 3 and MnO 2 (all with 5 N purity). These ingredients were ground thoroughly, calcined at several steps of 900 • C for 18 h, 1100 • C for 18 h, 1300 • C for 18 h, respectively, and finally sintered at 1400 • C. Thus prepared sample was powdered and PdO was added and pelletized.…”