Disorder-induced melting of the charge order in thin films of

¹ Kamerlingh Onnes Laboratory, Leiden University P.O. Box 9504, Leiden, the Netherlands
² Nijmegen High Field Magnet Laboratory Toernooiveld 1, 6525 ED Nijmegen, the Netherlands

Received: 20 December 2001
Accepted: 29 March 2002

Abstract

We have studied the magnetic-field–induced melting of the charge order in thin films of Pr_0.5Ca_0.5MnO₃ (PCMO) films on SrTiO₃ (STO) by X-ray diffraction, magnetization and transport measurement. At small thickness (25 nm) the films are under tensile strain and the low-temperature melting fields are of the order of 20 T or more, comparable to the bulk value. With increasing film thickness the strain relaxes, which leads to a strong decrease of the melting fields. For a film of 150 nm, with in-plane and out-of-plane lattice parameters closer to the bulk value, the melting field has reduced to 4 T at 50 K, with a strong increase in the hysteretic behavior and also an increasing fraction of ferromagnetic material. Strain relaxation by growth on YBa₂Cu₃O or by post-annealing yields even stronger reduction of the melting field. Apparently, strained films behave bulk-like. Relaxation leads to an increasing suppression of the CO state, presumably due to an atomic-scale disorder produced by the relaxation process.