Ferromagnetic ground state of the robust charge-ordered manganitePr0.5Ca0.5MnO3obtained by minimal Al substitution

Abstract

We show that minimal disturbance to the robust charge-ordered Pr 0.5 Ca 0.5 MnO 3 by 2.5% Al substitution on the Mn site drives the system toward a ferromagnetic ground state. The history-dependent coexisting phases observed are explained as the outcome of a hindered first-order transition with glasslike arrest of kinetics resulting in irreversibility. Consistent with a simple phase diagram having a ferromagnetic ground state, it is experimentally shown that these coexisting phases are far from equilibrium.

Conversion of a glassy antiferromagnetic-insulating phase to an equilibrium ferromagnetic-metallic phase by devitrification and recrystallization in Al substituted Pr0.5Ca0.5MnO3

“…3. This feature is consistent with T K , the temperature for glass-like arrest, falling as H rises 5,6 . It was shown earlier for variety of systems that broad H and T induced first-order transitions can be represented by quasi-continuum of supercooling (T*) lines, corresponding to spatial distribution of regions in the sample of the dimension of the correlation length, forming into T* bands in the H-T space.…”

“…5 . Hence, similar to LCMO, coexisting phases with different fractions of AF-I and FM-M phases can be created at low temperature in PCMAO 5,6 , one may be in equilibrium and the other in the 'magnetic glassy' state. The above mentioned measurements following the CHEF protocol shows that the AF-I phase partially transforms to FM-M on cooling, which is the converse of what is ob-served in LCMO.…”

“…It has been shown that minimal quench disorder in the magnetic lattice of Pr 0.5 Ca 0.5 MnO 3 in the form of 2.5% substitution of Al in Mn site 3 weakens the so called robust CO and 'finite size clusters' are formed 4 . It is shown that AF-I state of this system, Pr 0.5 Ca 0.5 Mn 0.975 Al 0.025 O 3 (PCMAO), can be converted to a FM-M state by moderate fields at low temperature 5 . However, the system does not get back to its original zero-field cooled (ZFC) state (AF-I) when the field is withdrawn isothermally.…”

“…Cooling in higher fields shows the AF-I to FM-M transformation with lowering temperature; the transition is hysteretic during warming. The fraction of the arrested AF-I phase can be tuned by cooling the sample in different fields (but at the same cooling rate), and this coexists with transformed FM-M phase at low temperature 5,6 .…”

“…Similar irreversibility in isothermal magnetization is observed in other half-doped manganites where it is proved that equilibrium phase at low temperature is AF-I 6,7 . Significantly, it is revealed from specially designed high field measurement protocols that this minimal substitutional disorder radically changes the low temperature AF-I equilibrium phase in the parent compound to FM-M in PCMAO 5,6 . 'Cooling and heating in equal field' (CHEF) shows that a fraction of AF-I phase transforms to FM-M phase with the decrease in temperature and the low temperature state shows coexisting FM-M and AF-I phases.…”