Influence of B - site Disorder in $La_{0.5}Ca_{0.5}Mn_{1-x}B_{x}O_{3}$ (B = Fe, Ru, Al and Ga) Manganites

TL;DR

This study investigates how different B-site dopants (Fe, Ru, Al, Ga) affect the structural and magnetic phases of La0.5Ca0.5MnO3, revealing complex doping-dependent magnetic transitions and phase coexistence.

Contribution

It provides a comprehensive analysis of the effects of various B-site dopants on the structural and magnetic properties of La0.5Ca0.5MnO3 using neutron diffraction, SANS, magnetization, and resistivity techniques.

Findings

Fe doping suppresses CE-type AFM and promotes ferromagnetic insulating phase.

Ru doping favors ferromagnetic metallic state with stable transition temperatures.

Al and Ga doping induce phase coexistence and eventually spin glass behavior.

Abstract

We have investigated the influence of B - site doping on the crystal and magnetic structure in $La_{0.5}Ca_{0.5}Mn_{1-x}B_{x}O_{3}$ (B= Fe, Ru, Al and Ga) compounds using neutron diffraction, SANS, magnetization and resistivity techniques. The B - site doped samples are isostructural and possess an orthorhombic structure in \textit{Pnma} space group at 300K. A structural transition from orthorhombic to monoclinic is found to precede the magnetic transition to CE - type antiferromagnetic state in few of these samples. On doping with Fe, charge and orbitally ordered CE - type antiferromagnetic state is suppressed, followed by the growth in ferromagnetic insulating phase in $0.02\leq x\leq0.06$ compounds. At higher Fe doping in $x>0.06$, the ferromagnetic state is also suppressed and no evidence of long range magnetic ordering is observed. In Ru doped samples $(0.01\leq x\leq0.05)$, the ferromagnetic metallic state is favored at $T{}_{C}\approx200K$ and $T_{MI}\approx125K$ and no significant change in $T_{C}$ and $T_{MI}$ as a function of Ru doping is found. In contrast, with non magnetic Al substitution for $0.01\leq x\leq0.03$, the charge ordered CE - type antiferromagnetic state coexists with the ferromagnetic metallic phase. With further increase in Al doping $(0.05\leq x\leq0.07)$, both CE - type antiferromagnetic and ferromagnetic phases are gradually suppressed. This behavior is accompanied by the evolution of A - type antiferromagnetic insulating state. Eventually, at higher Al doping $(0.10\leq x\leq0.13)$, this phase is also suppressed and signature of spin glass like transition are evident in M(T). Likewise, substitution with Ga is observed to induce similar effects as described for Al doped samples. The presence of short ranged ferromagnetic ordering has been further explored using SANS measurements in few of the selected samples.