Strain-induced time-dependent magnetic disorder in ultra-thin La sub(0.7)Ca sub(0.3)MnO sub(3) films

• Published in: Journal of magnetism and magnetic materials 1999-01, Vol.191 (3), p.359-367
• Main Authors: Blamire, M G, Teo, B-S, Durrell, J H, Mathur, N D, Barber, Z H, McManus Driscoll, J L, Cohen, L F, Evetts, J E
• Format: Article
• Language: English
• ISSN: 0304-8853

We report measurements of the electrical transport properties of films of La sub(0.7)Ca sub(0.3)MnO sub(3) deposited over a range of thicknesses on lanthanum aluminate and strontium titanate substrates. We find that the dependence of the resistance on temperature and magnetic field is very different in films with a thickness less than 10 nm which show a large mismatch-induced strain. We show that the hysteresis in the resistance of such films on changing the magnetic field is a consequence of logarithmic relaxation of the resistive state. We conclude these results, as well as similar data in the literature can be explained on the basis of a superparamagnetic state induced in ultra-thin films by local structural disorder. Since in the ultra-thin films a very high colossal magnetoresistance (CMR) > 1000% is maintained over a temperature range of over 200 K, films showing these effects may be more appropriate for applications than are thicker films in which the CMR effect is confined to a narrow temperature range near the Curie temperature.