Huge magnetoresistance and ultrasharp metamagnetic transition in polycrystalline Sm0.5Ca0.25Sr0.25MnO3

Large magnetoresistive materials are of immense interest for a number of spintronic applications, such as the development of high-density magnetic memory devices, magnetic sensors, and magnetic switches. Colossal magnetoresistance, in which the resistivity changes by several orders of magnitude (~ 104%) in an external magnetic field, occurs mainly in phase-separated oxide materials, namely, manganites, owing to the phase competition between the ferromagnetic metallic and antiferromagnetic insulating regions. Can the magnetoresistance be further enhanced by tuning the volume fraction of the two phases? In this work, we report a huge colossal magnetoresistance along with an ultrasharp metamagnetic transition in a half-doped Sm0.5Ca0.25Sr0.25MnO3 manganite compound by suitably tuning the volume fraction of the competing phases. The obtained magnetoresistance value at 10 K is as large as ~ 1013% in a 30 kOe external magnetic field and ~ 1015% in a 90 kOe external magnetic field and is several orders of magnitude higher than any other observed magnetoresistance value reported thus far. Using model Hamiltonian calculations, we have shown that the inhomogeneous disorder, deduced from tunneling electron microscopy, suppresses the CE-type phase and seeds the ferromagnetic metal in an external magnetic field. By tweaking the composition of magnetic materials, researchers have unlocked an enormous electrical switching effect useful for high-density data storage. When an external magnetic field is directed onto the materials consisting of manganese, samarium, strontium, and calcium, they can exhibit a property known as “colossal” magnetoresistance that transforms them from an insulating state to a state that is typically 10 thousand times more conductive. Indranil Das and Sanjib Banik from the Saha Institute of Nuclear Physics, Kolkata, India, and co-workers now report a technique to achieve quadrillion-fold differences in conductivity by optimizing concentrations of Mn, Sm, Sr, and Ca atoms. Electron microscopy revealed that the ”foreign” atoms create the regions of chemical disorder that seeded the growth of ferromagnetic phase, as shown by model Hamiltonian calculations, with metal-like conductivity after the magnetic field exposures and suppressed the formation of insulating phase. We observed huge magnetoresistance (~ 1015% in 90 kOe external magnetic field and 1013% in 30 kOe external magnetic field) at 10 K by engineering electronic phase separation in charge-ordered half-doped manganites. The observed huge value of magnetoresistance is explained by double-exchange model Hamiltonian calculations. Moreover, our electronic phase-controlled material, namely Sm0.5Ca0.25Sr0.25MnO3, shows an ultrasharp metamagnetic transition below 10 K, which is martensitic in nature. The many order of magnitudes higher magnetoresistance in Sm0.5Ca0.25Sr0.25MnO3 than any other magnetoresistive materials reported so far will motivate further experimental work.