Spectacular Effect of Doping upon Magnetism and Conductivity in Manganites

Bernard RAVEAU 


Manganites are very sensitive to the presence of impurities on the Mn sites of the perovskite structure. In this respect, the doping of orbital-charge ordered manganites, such as Ln0.5Ca0.5MnO3 or Ln0.4Ca0.6MnO3 by various elements is spectacular. Starting from the antiferromagnetic CE-type insulator, two classes of materials can be generated, depending on the nature of the dopant : for non magnetic elements (Al, Ga, Ti, Sn, In, Sc, Mg) and iron, spin glass insulators are obtained whereas for magnetic cations (Cr, Co, Ni, Cu, Rh, Ir, Ru), metallic ferromagnets are generated. As a consequence, the doping at Mn sites modifies dramatically the magnetic phase diagrams of the manganites, even for the LaMnO3 phase alone which by doping with varioius cations (Zn, Li, Mg, Co, Ni) becomes ferromagnetic, due to valency effects.
At very low temperature, (T - 5K) anomalies in the magnetic and transport properties are induced in the charge ordered manganites, either by doping at the manganese sites with various cations, or by doping at the calcium sites with larger cations like barium and strontium. Plotting the magnetization versus the applied magnetic field, a step like behaviour is observed which is strongly influenced by the nature of the dopant, its content, thermal cycling etc. Importantly, a correlated effect is observed on the resistivity which can vary by several orders of magnitude in the form of steps. This effect is also detected on the variation of the specific heat versus the applied magnetic field. These properties are closely related to the phase separation phenomena that appear in the manganites. This peculiar behaviour also detected from neutron diffraction data, can be interpreted by a martensic like mechanism.


Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium D, by Bernard RAVEAU
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-26 14:34
Revised:   2009-06-08 12:55