Magnetoresistive memory in phase separated La_{0.5}Ca_{0.5}MnO_{3}

JOAQUIN SACANELL; F. PARISI; P. LEVY; L. GHIVELDER

Buenos Aires, Argentina

Workshop; At the frontiers of Condensed Matter 2004; 2004

CNEA

In this work we have studied the non-volatile memory effect the phase separated (PS) compound La0.5Ca0.5MnO3. Upon lowering temperature, this compound first undergoes a paramagnetic to ferromagnetic (FM) phase transition at TC ~ 225 K, and then to a charge ordered antiferromagnetic phase at Tco ~ 150 K, so this system has an important COAFM fraction at low T. We have shown that the response of the system to the application of a magnetic field depends on the temperature range involved, due to the existence of three well-differentiated PS regimes: ‘‘soft PS’’ for TC> T > 200 K , ‘‘intermediate’’ PS for 200 K > T > Tco , and ‘‘hard PS’’ for T < Tco. We have studied two ways of imprinting distinct values of H, hereafter referred as ZFC and FC procedures. ZFC procedure: The sample is cooled in zero field for resistivity measurements and in a low H0 (~ 0.1 T) for magnetization (M). Then different values of Hap (>H0 for M measurements) are applied and turned off during cycles of ~1 hour. Either r or M are measured during the whole experiment. For T > 200 K and T < 70 K, the system has no memory of the applied Hap and recovers its H=0 state once the field is turned off. For 150 K < T < 200 K, the compound shows a reduction of the r and an increase of M during the application of distinct values of Hap. Once the field is turned off, the system does not recover its H=0 state and its subsequent M and r values depends on the previous Hap. The physical properties show no changes if, after the application of Hap1, Hap2 < Hap1 is applied. From these results, we infer an increase of f after each Hap-on / Hap-off procedure. For 70 K < T < 150 K, the effect is similar but it’s at least one order of magnitude smaller. FC procedure: The sample is cooled in the field cooling procedure (FC) in HFC ~ 1 T. Then H is lowered by the “application” of different values of dHap < 0 that are “turned on” and “turned off” during cycles of ~1 hour. The HFC serves to force a highly FM state and the application of dHap < 0, results in a reduction of f. So in this procedure, the memory is imprinted in an increase of non – FM regions. For T > 200 K and T < 70 K, the system has no memory and the process of apply and turn off the dHap is reversible. For 70 K < T < 150 K, the compound shows a huge reduction of M during the application of distinct values of dHap. Once the dHap is turned off, the system does not recover its HFC state and its M value depend on the previous dHap. The physical properties show no changes if, after the application of dHap1, dHap2 (with |dHap2|< |dHap1|) is applied. From these results, we infer a reduction of f after each dHap – on / dHap – off procedure. During the application of dHap, an evolution of M can be seen that indicates the increase of non – FM regions (after the rapid change due to the misalignment of FM domains). For 150 K < T < 200 K, the effect is similar but it’s at least one order of magnitude smaller.We have obtained that the memory effect is greater when we apply the field in the FC procedure.