TY - JOUR
T1 - Raman scattering studies of the temperature- and field-induced melting of charge order in Lax Pry Ca1-x-y MnO3
AU - Kim, M.
AU - Barath, H.
AU - Cooper, S. L.
AU - Abbamonte, P.
AU - Fradkin, E.
AU - Rübhausen, M.
AU - Zhang, C. L.
AU - Cheong, S. W.
PY - 2008/4/3
Y1 - 2008/4/3
N2 - We present Raman scattering studies of the structural and magnetic phases that accompany temperature- and field-dependent melting of charge- and orbital-order (COO) in La0.5 Ca0.5 MnO3 and La0.25 Pr0.375 Ca0.375 MnO3. Our results show that thermal and field-induced COO melting in La0.5 Ca0.5 MnO3 exhibits three stages in a heterogeneous melting process: At low temperatures and fields we observe a long-range, strongly Jahn-Teller (JT) distorted-COO phase; at intermediate temperatures and/or fields, we find a coexistence regime comprising both strongly JT distorted-COO and weakly JT distorted/ferromagnetic metal (FMM) phases; and at high temperatures and/or high fields, we observe a weakly JT distorted homogeneous paramagnetic (PM) or ferromagnetic (FM) phase. In the high field-high temperature regime of La0.5 Ca0.5 MnO3 and La0.25 Pr0.375 Ca0.375 MnO3, we identify a clear structural change to a weakly JT distorted phase that is associated with either a Imma or Pnma structure. We are able to provide a complete structural phase diagram of La0.5 Ca0.5 MnO3 for the temperature and field ranges 6≤T≤170 K and 0≤H≤9 T. Significantly, we provide evidence that the field-induced melting transition of La0.5 Ca0.5 MnO3 is first-order, and resembles a crystallization transition of an "electronic solid." We also investigate thermal and field-induced melting in La0.25 Pr0.375 Ca0.375 MnO3 to elucidate the role of disorder in melting of COO. We find that while thermal melting of COO in La0.25 Pr0.375 Ca0.375 MnO3 is quite similar to that in La0.5 Ca0.5 MnO3, field-induced melting of COO in the two systems is quite different in several respects: The field-induced transition from the COO phase to the weakly JT-distorted-FM phase in La0.25 Pr0.375 Ca0.375 MnO3 is very abrupt, and occurs at significantly lower fields (H∼2 T at T∼0 K) than in La0.5 Ca0.5 MnO3 (H∼30 T at T=0 K); the intermediate coexistence regime is much narrower in La0.25 Pr0.375 Ca0.375 MnO3 than in La0.5 Ca0.5 MnO3; and the critical field Hc increases with increasing temperature in La0.25 Pr0.375 Ca0.375 MnO3, in contrast to the decrease in Hc observed with increasing temperature in La0.5 Ca0.5 MnO3. To explain these differences, we propose that field-induced melting of COO in La0.25 Pr0.375 Ca0.375 MnO3 is best described as the field-induced percolation of FM domains, and we suggest that Griffiths phase physics may be an appropriate theoretical model for describing the unusual temperature- and field-dependent transitions observed in La0.25 Pr0.375 Ca0.375 MnO3.
AB - We present Raman scattering studies of the structural and magnetic phases that accompany temperature- and field-dependent melting of charge- and orbital-order (COO) in La0.5 Ca0.5 MnO3 and La0.25 Pr0.375 Ca0.375 MnO3. Our results show that thermal and field-induced COO melting in La0.5 Ca0.5 MnO3 exhibits three stages in a heterogeneous melting process: At low temperatures and fields we observe a long-range, strongly Jahn-Teller (JT) distorted-COO phase; at intermediate temperatures and/or fields, we find a coexistence regime comprising both strongly JT distorted-COO and weakly JT distorted/ferromagnetic metal (FMM) phases; and at high temperatures and/or high fields, we observe a weakly JT distorted homogeneous paramagnetic (PM) or ferromagnetic (FM) phase. In the high field-high temperature regime of La0.5 Ca0.5 MnO3 and La0.25 Pr0.375 Ca0.375 MnO3, we identify a clear structural change to a weakly JT distorted phase that is associated with either a Imma or Pnma structure. We are able to provide a complete structural phase diagram of La0.5 Ca0.5 MnO3 for the temperature and field ranges 6≤T≤170 K and 0≤H≤9 T. Significantly, we provide evidence that the field-induced melting transition of La0.5 Ca0.5 MnO3 is first-order, and resembles a crystallization transition of an "electronic solid." We also investigate thermal and field-induced melting in La0.25 Pr0.375 Ca0.375 MnO3 to elucidate the role of disorder in melting of COO. We find that while thermal melting of COO in La0.25 Pr0.375 Ca0.375 MnO3 is quite similar to that in La0.5 Ca0.5 MnO3, field-induced melting of COO in the two systems is quite different in several respects: The field-induced transition from the COO phase to the weakly JT-distorted-FM phase in La0.25 Pr0.375 Ca0.375 MnO3 is very abrupt, and occurs at significantly lower fields (H∼2 T at T∼0 K) than in La0.5 Ca0.5 MnO3 (H∼30 T at T=0 K); the intermediate coexistence regime is much narrower in La0.25 Pr0.375 Ca0.375 MnO3 than in La0.5 Ca0.5 MnO3; and the critical field Hc increases with increasing temperature in La0.25 Pr0.375 Ca0.375 MnO3, in contrast to the decrease in Hc observed with increasing temperature in La0.5 Ca0.5 MnO3. To explain these differences, we propose that field-induced melting of COO in La0.25 Pr0.375 Ca0.375 MnO3 is best described as the field-induced percolation of FM domains, and we suggest that Griffiths phase physics may be an appropriate theoretical model for describing the unusual temperature- and field-dependent transitions observed in La0.25 Pr0.375 Ca0.375 MnO3.
UR - http://www.scopus.com/inward/record.url?scp=41749107124&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=41749107124&partnerID=8YFLogxK
U2 - 10.1103/PhysRevB.77.134411
DO - 10.1103/PhysRevB.77.134411
M3 - Article
AN - SCOPUS:41749107124
SN - 1098-0121
VL - 77
JO - Physical Review B - Condensed Matter and Materials Physics
JF - Physical Review B - Condensed Matter and Materials Physics
IS - 13
M1 - 134411
ER -