GIANT MAGNETORESISTANCE EFFECT IN THE LAYERED PEROVSKITES (Ca,La)₄Mn₃O₁₀ F.J.Lincoln, Research Centre for Advanced Mineral and Materials Processing, University of Western Australia, Nedlands, W.A. Australia 6907, P. Goodman, and N. S.Witte, School of Physics, University of Melbourne, Parkville, Australia 3052, R.H.March, Physics Department, Dalhousie University, Halifax, Canada B3H3J5

Recent observations of giant magnetoresistance (GMR) in ABO₃ perovskites where B is Mn³⁺/Mn⁴⁺ and A is a rare earth/alkaline earth mix¹, and more recently, of similar observations within the family La_nSrMn_nO_3n+1, for n = 1,2 & ², has encouraged us to re-examine data collected recently³ on a different but related series. In above series²,the compounds start with Mn in the Mn³⁺ state and achieve a finite Mn⁴⁺ population by Sr doping. Our approach was the reverse: we start from an initial Mn⁴⁺compound and introduce an Mn³⁺population by La³⁺ doping of the Ca²⁺ site. Using a combination of AC susceptibility, resistivity and neutron diffraction observations we examined three phases Ca_(n+1)-xLa_xMn_nO_3n+1, with n=3, and x values 0, 0.01 & 0.1.

With increasing doping we find a drop in peak resistivity of 10⁷ . Although all three samples have semiconducting character following the thermal activation law above 100K, between 77K and 100K this law cannot account for our data. Also we find antiferromagnetic ordering, present in the undoped sample, disappearing in the doping interval 0.01 to 0.1. We predict that with higher La³⁺ doping a paramagnetic metallic phase will emerge, and that at this phase boundary the system will exhibit Giant Magnetoresistance.

1. Raveau, Maignan, & Caignaert (1995), J.Sol.State.Chem.117,424.

2. Moritomo, Asamitsu, Kuwahara & Tokura (1996) Nature 380, 141.

3. Rossell, Goodman, Bulcock, March, Kennedy, White, Lincoln & Murray (1996), Australian J. of Chemistry 49, 205-217.