DCMPMS Seminars

Physical properties of 3d-electron based correlated systems Mn1-xFexSi and Fe1-yCoySi : Specific heat and resistivity investigations

by Mr. S. Shanmukharao Samatham (Research Scholar, Low Temperature Laboratory, UGC-DAE CSR, Indore)

Tuesday, April 28, 2015 from to (Asia/Kolkata)
at AG80
Description
Investigation of effect of magnetic fields on the physical properties (resistivity and specific heat) of 3d-electron based correlated systems is presented. In MnSi, the presence of skyrmions and chiral modulation crossovers and phase transitions of MnSi in the vicinity of long range magnetic ordering temperature (Tc~29.7 K) are investigated. The notable anomalies in specific heat as a function of magnetic fields which directly correspond to the speculated chiral modulations in the precursor region are observed. The magneto-thermal (H-T) phase diagram reveals the existence of repulsive, attractive and confined skyrmion phases. Resistivity analysis suggests strong electron-magnon coupling as well as the possibility of strong electron correlations in MnSi supported by Kadowaki-Woods ratio (A/γ2).
Low temperature ground state properties of Mn1-xFexSi (x=0.25) are investigated based on T- and H-dependent specific heat and resistivity. Paramagnon spin fluctuations assisted non-Fermi liquid is suppressed by magnetic fields and gradual evolution of field-tuned Fermi liquid is described. Magnetic field (H) induced crossover is illustrated by suitable specific heat scaling which reveals quantum critical phenomenon (QCP). At H=0 T, Kadowaki-Wood's Ratio (KWR) A/γ2 is about 8.5 μΩ cm.mol2.K2.J-2 which is 85% close to the originally proposed KWR and it becomes 100% under moderate fields of about 0.7 T. An unusual QCP is observed in an electron correlated paramagnet in two steps. Firstly, suppression of magnetic ordering by chemical doping (Fe at Mn site in MnSi) and secondly converting non-Fermi liquid to Fermi liquid by external magnetic fields.
Qualitative analysis of electron doped correlated semiconductor, Fe1-yCoySi is carried out based on resistivity and specific heat. The estimated Sommerfeld parameter γ exactly follows the calculated density of states as a function of doping. Studies under magnetic fields reveal positive magnetoresistance for the entire solid solution Fe1-yCoySi. Decrease of γ0 with fields may corroborate with the observed positive magnetoresistance. Zero magnetic fields investigation of thermodynamic and transport investigations on CoSi reveal the existence of pseudogap of about 13 meV.