Spin Nematicity and Large Low‐Field Positive Magnetoresistance in a Half‐Doped Manganite: An Approach Exploiting Cation Size Disorder

Abstract

ELC states should arise from strong electron correlations. However, a clear picture is still far from completed, especially for transition metal oxides where the interplay between spin, charge and orbital degrees of freedom is ineluctably complex. On the other hand, how essentially the ELC states would grant exotic physical properties remains to be elucidated in spite of relentless efforts.In general ELC states are expected to stay away from even a weak material disorder. [ 2,21 ] In this work, we however report an exploring of spin nematic phase in perovskite manganites (La 1-x Y x ) 0.5 (Ca 1-y Sr y ) 0.5 MnO 3 (LYCS) by increasing cation size disorder ( σ 2 ), quantifi ed by q r rwhere q i is the fractional occupancies of A-site species in the ABO 3 type structure, r i and r A are the individual and mean ionic radius, respectively. [ 22,23 ] The parent oxide La 0.5 Ca 0.5 MnO 3 is a prototypical half-doped manganite and is well known for its antiferromagnetic (AFM) charge-exchange (CE) type charge-orbital ordering (COO). [ 24,25 ] Recently, a real-space imaging study of this compound by Tao et al. reveals a nanoscale phase separation, presenting as randomly distributed charge disordering (CD) droplets in the AFM-COO matrix. [ 11 ] It is therefore of keen interest to see if the CD droplets could be elongated and textured, and with possible enhanced spin moments driven by magnetic symmetry breaking. Note that there exist the following relations for the cation ionic size: r r [ 23 ] A cation size mismatch and disorder already presents at x = y = 0 ( σ 2 = 0.0003 Å 2 ). By tuning the (Y,Sr) ratios at the A site in LYCS, one can fi x r A and the hole doping while increase the cation size disorder, [ 26 ] which would further break the AFM-COO symmetry and thus create an expanded CD phase in ELC states. Here, with detailed magnetic and electrical measurements, we demonstrate that a spin nematic phase can be indeed separated from the weakened AFM-COO matrix by a minor σ 2 = 0.001 Å 2 , and remarkably, such an ELC state can yield large positive as well as negative magnetoresistance under external magnetic fi elds much lower than that required for the conventional colossal magnetoresistance (CMR).In principle, material disorder such as random dopants disfavors the long range electronic liquid crystal (ELC) order in quantum matters. It is reported that a minor A site cation size disorder ( σ 2 = 0.001 Å 2 ) in half-doped manganites (La 1-x Y x ) 0.5 (Ca 1-y Sr y ) 0.5 MnO 3 interestingly leads to spin nematicity which is accompanied by a large positive magnetoresistance (up to 40%) at fi elds ( H ≤ 1 kOe at 60 K) much lower than that ( H cr ≈ 35 kOe) critical for melting the weakened antiferromagnetic charge-orbital ordering (AFM-COO). The spin nematicity, emerging with a suppressed orthorhombicity, is ascribed to the destabilization of the d 3 x 2 -r 2 / d 3 y 2 -r 2 orbital stripe alternation and the consequent magnetic symmetry breaking. The non-trivial low fi eld magnetoresistance is found to be determined by the spi...

Emergence of ferromagnetism and metallicity in Pr0.5Sr0.5MnO3 nanoparticles

“…[1][2][3][4] The exotic physical and magnetic properties arising from these states can be controlled by small external perturbations like a magnetic and electric field, hydrostatic pressure and/or stoichiometric chemistry of the compound, which could have the drastic impact in the area of fundamental research and for spintronic applications. [5][6][7] Quite interestingly, by reduction of particle size in the nanometric scale similar fascinating properties can be obtained, which emphasize a strong ligature between two. [8][9][10][11][12][13] Recently, Jirak et al 14 at room temperature probing X-ray and neutron scattering experiments, which revealed that structural parameters remain almost unaffected with reduction of particle size.…”

Facile Synthesis, Magnetic and Electric Characterization of Mixed Valence La0.75K0.25AMnTiO6 (A = Sr and Ba) Perovskites

“…Thus, more in-depth studies should be carried out on such Ti-doped system and new room-temperature ferromagnetic materials can be expected by ion doping. In view of the great influence of the oxidation state on the structure and properties in manganite perovskites, − up to now, most efforts have been devoted to adjusting the stoichiometric ratio or vacancies of Ln 1– x A x ­Mn­TiO 6 . However, alkaline-metal doping is another efficient route to tune the properties of manganites to desired functionalities, such as enhanced ferromagnetism in La 1– x Na x ­MnO 3 ( T C ∼ 327 K) and increased magneto-resistance in La 1– x K x ­MnO 3 .…”