La <sub> 0.75 </ Sub> Sr <sub> 0.25-xy </ Sub> A <sub> X </ Sub> ¡õ <sub> Y </ Sub> Mno <sub> 3 </ Sub> (a = Cu, K) At Room Temperature Magnetoresistance Effect Study

Since the 90's in last century, When the colossal magneto-resistance effect in rare-earth manganite perovskites was found, it has attracted considerable attention in scientific studies due to its special physics mechanism and the potential application in fields of magnetic record and magnetic sensor and so on.However, the poor temperature dependence of MR, the low-temperature MR effect, and the ideal MR only in high field, severely limit their practical utilities. Many researches have thus been concentrated on making new material system that can provides low field magnetoresistance (LFMR) around room temperature. On the other hand, recent efforts to broaden the CMR temperature range have been made by means of the different element substitution.In this paper, La_0.75Sr_0.25x-7A_xâ–¡_yMnO₃(A=Cu, K,â–¡ represents vacancy) samples were prepared by sol-gel method , their structure ^ electrical and magnetic properties were researched in detail.There are several interesting results we have got:1. The phase identification of samples has been carried out by the X-ray diffraction (XRD) with a Rigaku max-RB dififractometer with Cu K? radiation. The results indicate that the materials are a single phase rhombohedral perovskite structure without any other secondary phase. When the dope content x<0.07, the lattice parameter a, c and the cell volume v of La_0.75Sr_0.25xA_xMnO₃ (A=Cu, K) samples without vacancy monotonically increased with the dope content x. When x = 0.10 , the cell volume of the La_0.75Sr₀₁₅K_0.10MnO₃ sample decreased in some measure. For the samples La_0.75Sr_0.25-x-yCu_xâ–¡_yMnO₃ and La_0.75Sr_0.25x-yK_xâ–¡_yMnO₃ (â–¡ represent vacancy) with different x and y, the change of a , c and v have themselves characters .2. The granule morphology in powder samples was obtained by S-570 scanning electron microscopy (SEM). The results show that the particles in powder samples are closed to globular shape and the particle size which doped by different element is different .The size of Cu-doped sample is about 95nm, while it of K-doped sample is about 120nm.3. From the magnetic measurement result, we find that all the samples are soft magnetic...