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

Abstract

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≈0.42, y≈0.40) in t~20–140nm thick films deposited on LaAlO3 (001) substrates. The ferromagnetic (FM) transition temperature (TC) first decreases as the film thickness is increased from t~20nm to t~60nm 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≥60nm shows pronounced hysteresis and ΔTC=TCFCW−TCFCC decreases concomitantly from 46K to 35K as the thickness increases from ~60 to ~140nm. The thinnest film shows insulator to metal transitions (IMT) only at magnetic field H>40kOe. Films with t≥TC show sharp hysteretic IMT, with ΔTIM=TIMW−TIMC decreasing from ~70K to ~50K as the thickness increases from ~60nm to ~140nm. 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 ΔTIM 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.