Electronic and Magnetic Properties of Sr and Ca Doped Lanthanum Manganites transfrom First-Principles

M.–H. Tsai*, Y.–H. Tang,H. Chou, and W. T. Wu

Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424 Taiwa


Abtract

The complicated electronic, magnetic, and colossal magnetoresistant (CMR) properties of Sr and Ca doped lanthanum manganites can be understood by spin-polarized first-principles calculations. The electronic propertiescan be attributed toadetailed balancing between Sr and Ca inducedmetal-likeO 2pand majority-spin (↑-spin) Mn eg delocalized states and the insulator-like minority-spin (↓-spin) Mn t2g band near the Fermi level (EF). The magnetic properties can be attributed toadetailed balancing between O mediated antiferromagnetic superexchange and delocalized↑-spin Mneg-state mediated ferromagnetic spin-spin couplings. While CMR can be attributed to the lining up of magnetic domains trigged by theapplied magnetic field, which suppresses thetrapping ability of the empty Mn t2g states that resists the motion of conducting Mn↑-spin eg electron.

https://arxiv.org/ftp/cond-mat/papers/0604/0604367.pdf 

 III. RESULTS AND DISCUSSION 

(a)Magnetic states

The total energies per Mn ion, i.e. the totalenergy per unit cell divided by the number of Mnions in the unit cell, of the mostfavorable antiferromagnetic state relative to that of theferromagnetic state are shown in Table I.The totalenergy results show that LaMnO3, La0.50Ca0.50MnO3, La0.50Sr0.50MnO3, La0.25Ca0.75MnO3 ,and La0.25Sr0.75MnO3 are A-typ eantiferromagnetic, La0.75Ca0.25MnO3 and La0.75Sr0.25MnO3 are ferromagnetic, and CaMnO3and SrMnO3are G-type antiferromagnetic.The A-type antiferromagnetic state of La0.25Sr0.75MnO3, which is only slightly more favorable than the C-type antiferromagnetic state by0.13eV per 40-atom unit cell, disagrees with the C-type antiferromagnetic state shown in the phase diagram of La1-xSrxMnO3.35 .This discrepancy may be due to the particular crystal structure used in this study. Except La0.25Sr0.75MnO3, the calculated magnetic states of these manganites agree with those shown in the phase diagrams of La1-xSrxMnO3 and La1-xCaxMnO3.