Multiple magnetic transitions, dynamical magnetic liquid and magnetic glass in La1-x-yPryCaxMnO3 (x approximate to 0.42, y approximate to 0.40) thin films: A thickness dependent study

The influence of substrate induced strain and its relaxation on the evolution of the multiple magnetic transitions and ensuing modifications in the degree of phase separation, the nature of the dynamical magnetic liquid, the randomly frozen glass and insulator-metal transitions have been investigated in single crystalline La1-x-yPryCaxMnO3 (x approximate to 0.42, y approximate to 0.40) in t similar to 20-140 nm thick films deposited On LaAlO3 (001) substrates. The ferromagnetic (FM) transition temperature (T-C) first decreases as the film thickness is increased from t similar to 20 nm to t similar to 60 nm and then increases with increasing film thickness. In contrast the charge ordering (CO), antiferromagnetic (AFM) and glass transition temperatures shift towards higher values with increasing film thickness. The field cooled cooling (FCC) and field cooled warming (FCW) magnetization (M-T) of films having t >= 60 nm shows pronounced hysteresis and Delta T-C=T-C(FCW) T-C(FCC) decreases concomitantly from 46 K to 35 K as the thickness increases from similar to 60 to similar to 140 nm. The thinnest film shows insulator to metal transitions (IMT) only at magnetic field H > 40 kOe. Films with t >= T-C show sharp hysteretic IMT, with Delta T-IM=T-IM(W)-T-IM(C) decreasing from similar to 70 K to similar to 50 K as the thickness increases from similar to 60 nm to similar to 140 nm. Such strong hysteresis is a characteristic of first order phase transition and also a signature of magnetic liquid like phase created by the magnetic frustration created by the delicate balance between FM and AFM/CO phases. The H induced AFM/CO to FM transition reduces Delta T-IM and at higher fields the phase transition appears akin to the second order. The observed difference in the magnetic and transport properties have been explained in terms of the substrate induced strain at lower film thickness and its relaxation at higher thickness.