Coexisting tunable fractions of glassy and equilibrium long-range-order phases in manganites

Abstract

Antiferromagnetic-insulating(AF-I) and the ferromagnetic-metallic(FM-M) phases coexist in various half-doped manganites over a range of temperature and magnetic field, and this is often believed to be an essential ingredient to their colossal magnetoresistence. We present magnetization and resistivity measurements on Pr 0.5 Ca 0.5 Mn 0.975 Al 0.025 O 3 and Pr 0.5 Sr 0.5 MnO 3 showing that the fraction of the two coexisting phases at low-temperature in any specified measuring field H, can be continuously controlled by following designed protocols traversing field-temperature space; for both materials the FM-M fraction rises under similar cooling paths. Constant-field temperature variations however show that the former sample undergoes a 1st order transition from AF-I to FM-M with decreasing T, while the latter undergoes the reverse transition. We suggest that the observed path-dependent phase-separated states result from the low-T equilibrium phase coexisting with supercooled glass-like high temperature phase, where the low-T equilibrium phases are actually homogeneous FM-M and AF-I phases respectively for the two materials.

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.…”

“…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.…”

Martensite-like transition and spin-glass behavior in nanocrystalline Pr0.5Ca0.5MnO3

“…12 The reverse cycle (170 kOe→0) trace does not overlap with the warm up curve indicating a substantial magnetic hysteresis, 12 the effect being more pronounced at lower T. The observed M-H loop area gradually closes as the sample is warmed up to 70 K. Similar features were earlier reported 12 by conventional DC SQUID measurements performed on PCMO20, PCMO40, on Nd 0.5 Ca 0.5 MnO 3 nanoparticles 19 as well as on Al doped bulk PCMO. 20 Also, much sharper stair-case like metamagnetic transitions were seen in several other Pr and Nd based bulk manganites. 21,22 The possible reason 21 for the current broadened transition could be that the spins are strongly coupled to the lattice, hindering the kinetics of AFM to FM phase transitions.…”

First order magneto-structural transition and magnetocaloric effect in MnNiGe0.9Ga0.1

“…They speculated that the presence of some of the arrested FM phase fraction along with the AFM phase could also be responsible for such an increase in the overall M at low temperatures. In order to ascertain this, M (T ) was measured under cooling and heating in unequal magnetic field protocol [25] i.e. M (T ) was measured during heating under H = 1 T after cooling at different fields (H an ) [see Fig.…”