NGHIÊN CỨU CHUYỂN PHA VÀ CÁC TÍNH CHẤT ĐIỆN, TỪ TRONG CÁC HỢP CHẤT La2/3Ca1/3Mn1-xTMxO3- (TM = Cu VÀ Zn)

Abstract

STUDY ON PHASE TRANSITION, ELECTIC AND MAGNETIC PROPERTIES OF  La_2/3Ca_1/3Mn_1-xTM_xO_3-d (TM = Cu and Zn) COMPOUNDS

The perovskite La_1-xCa_xMnO₃ system has many particular properties with x = 1/3. At this doping concentration, the ferromagnetic-paramagnetic (FM-PM) phase transition temperature (T_C) and the metallic-insulator (M-I) phase transtion temperature (T_p) of the compound reach to maximum values. Besides, magnetoresistance effect of the compound is large at low magnetic field. To develop Mn-based perovskite compounds, direct substitutions of Mn by other 3d transition metals (TM) in the La_2/3Ca_1/3MnO₃ compound have been made. The previous studies show that the electronic and magnetic properties of La_2/3Ca_1/3Mn_1-xTM_xO₃ compounds are variously changed in comparison to these of the La_2/3Ca_1/3MnO₃ compound, but explanation in literature are not enough to shed light on physical mechanisms of these changes.

This paper showed new results of the electronic and magnetic properties of La_2/3Ca_1/3Mn_1-xTM_xO₃ (with TM = Cu and Zn) compounds, in order to clarify more about physical mechanisms underlying the various changes in properties of the compounds by substituting other TM for Mn. It is found that there are three important reasons to explain the changes in the electronic and magnetic properties of La_2/3Ca_1/3Mn_1-xTM_xO₃ compounds: (i) imperfect ferromagnetic ordering, (ii) decreasing mobility of e_g electrons, and (iii) increasing strength of Jahn-Teller distortion by substituting Cu or Zn for Mn.