Paramagnetic anomalies above the Curie temperature and colossal magnetoresistance in optimally doped manganites

Electron paramagnetic resonance measurements for (La,Y)2/3(Ca,Ba)1/3MnO3

“…4 for four representative samples. Similar behavior has been generally reported on manganese perovskites [17][18][19]. As indicated in the figure, all samples show a common feature in linewidth: the DH pp first shows a linear decrease with lowering temperature, reaches a minimum at T min and then increases anomalously on further cooling.…”

“…Previous investigations on magnetic properties have generally placed emphasis upon measurements of magnetization below and susceptibility above T c : From these measurements, one concludes that the Ln 2=3 A 1=3 MnO 3 compounds with /r A SX/r A S c show PM behavior above and FM behavior below T c : However, experiments, such as neutron scattering [14] and small angle neutron scattering [15], demonstrate the presence of small FM clusters in the PM background; while the measurement of scanning tunneling spectroscopy [16] directly confirms the coexistence of PM and FM regions around T c : On the other hand, several reports [17][18][19] on the measurements of electron paramagnetic resonance (EPR) have shown that PM anomalies occur upon cooling towards T c : These observations suggest that the question of the ground state around T c should be subtle. In the present work, we report a systematic study of EPR for a series of ðLa 1Àx Y x Þ 2=3 A 1=3 MnO 3 perovskite compounds with /r A S basically covering the whole region of /r A SX/r A S c ; where A= Ca and Ba.…”

Unusual magnetic and transport properties above the Curie temperature in La2/3Ca1/3MnO3

“…For the optimum composition with xw1/ 3, the largest CMR appears near a temperature T IM at which the insulator-metal (I-M) transition occurs [4]. It is further noted [4] that the CMR near T IM is found to exhibit Tdependent behavior similar to that for the resistivity (r) versus T dependence measured in zero magnetic field, suggesting a close correlation in the underlying physical origin of both the CMR and the I-M transition. Clearly, in order to reveal the true nature of CMR, one first needs to understand the origin of the I-M transition.…”

“…Although the CMR has been intensively studied, the physical mechanism is still controversial [3]. For the optimum composition with xw1/ 3, the largest CMR appears near a temperature T IM at which the insulator-metal (I-M) transition occurs [4]. It is further noted [4] that the CMR near T IM is found to exhibit Tdependent behavior similar to that for the resistivity (r) versus T dependence measured in zero magnetic field, suggesting a close correlation in the underlying physical origin of both the CMR and the I-M transition.…”

Effect of Eu doping on structural and magneto-electrical properties of La0.7Ca0.3MnO3 manganites

“…The growth of interest in their properties stems in large part from their wide range of technological applications such as read heads for magnetic information storage, low and high field magnetic sensors and more recently spintronic applications [4][5][6]. Numerous studies have been devoted in the rare earth manganite perovskite with the series of (La 1−x RE x ) 2/3 Ca 1/3 MnO 3 (RE is trivalent rare earth elements such as Y, Pr, Eu, and Sm) which are exhibiting colossal magnetoresistance (CMR) properties [7,8]. These compounds are Mn 3+ rich and doping with divalent atoms introduces mixture valency of Mn 3+ and Mn 4+ ions that plays a major role in the double exchange (DE) ferromagnetic interaction coupled with metallic resistivity [9].…”