arXiv subjects

Sarita Rajput

Publications and source records attributed to Sarita Rajput.

5 recordsLinked to original sources

arXiv2022

The effect of antisite disorder on magnetic and exchange bias properties of Gd-substituted Y$_2$CoMnO$_6$ double perovskite

Combining experimental investigations and first-principles DFT calculations, we report physical and magnetic properties of Gd-substituted Y$_2$CoMnO$_6$ double perovskite, which are strongly influenced by antisite-disorder-driven spin configurations. On Gd doping, Co and Mn ions are present in mixed-valence (Co$^{3+}$, Co$^{2+}$, Mn$^{3+}$ and Mn$^{4+}$) states. Multiple magnetic transitions have been observed: i) paramagnetic to ferromagnetic transition is found to occur at \textit{T}$_C$=95.5 K, ii) antiferromagnetic transition at \textit{T}$_N$=47 K is driven by $3d-4f$ polarisation and antisite disorder present in the sample, iii) change in magnetization below \textit{T}$\leq$20 K, primarily originating from Gd ordering, as revealed from our DFT calculations. AC susceptibility measurement confirms the absence of any spin-glass or cluster-glass phases in this material. A significantly large exchange bias effect (\textit{H}$_{EB}$=1.07 kOe) is found to occur below 47 K due to interfaces of FM and AFM clusters created by antisite-disorder.

cond-mat.mtrl-sci↗

arXiv2021

Coexisting magnetic structures and spin-reorientation in Er$_{0.5}$Dy$_{0.5}$FeO$_{3}$: Bulk magnetization, neutron scattering, specific heat, and \emph{Ab-initio} studies

The complex magnetic structures, spin-reorientation and associated exchange interactions have been investigate in Er$_{0.5}$Dy$_{0.5}$FeO$_3$ using bulk magnetization, neutron diffraction, specific heat measurements and density functional theory calculations. The Fe$^{3+}$ spins order as G-type antiferromagnet structure depicted by $Γ_{4}$($G_{x}$,$A_{y}$,$F_{z}$) irreducible representation below 700K, similar to its end compounds. The bulk magnetization data indicate occurrence of the spin-reorientation and rare-earth magnetic ordering below $\sim$75 K and 10 K, respectively. The neutron diffraction studies confirm an "incomplete" $Γ_{4}$${\rightarrow}$ $Γ_{2}$($F_{x}$,$C_{y}$,$G_{z}$) spin-reorientation initiated $\leq$75 K. Although, the relative volume fraction of the two magnetic structures varies with decreasing temperature, both co-exist even at 1.5 K. At 8 K, Er$^{3+}$/Dy$^{3+}$ moments order as $c_{y}^R$ arrangement develop, which gradually increases in intensity with decreasing temperature. At 2 K, magnetic structure associated with $c_{z}^R$ arrangement of Er$^{3+}$/Dy$^{3+}$ moments also appears. At 1.5 K the magnetic structure of Fe$^{3+}$ spins is represented by a combination of $Γ_{2}$+$Γ_{4}$+$Γ_{1}$, while the rare earth moments coexists as $c_{y}^R$ and $c_{z}^R$ corresponding to $Γ_{2}$ and $Γ_{1}$ representation, respectively. The observed Schottky anomaly at 2.5 K suggests that the "rare-earth ordering" is induced by polarization due to Fe$^{3+}$ spins. The Er$^{3+}$-Fe$^{3+}$ and Er$^{3+}$-Dy$^{3+}$ exchange interactions, obtained from first principle calculations, primarily cause the complicated spin-reorientation and $c_{y}^R$ rare-earth ordering, respectively, while the dipolar interactions between rare-earth moments, result in the $c_{z}^R$ type rare-earth ordering at 2 K.

cond-mat.str-el↗

arXiv2020

Emergence of weak pyrochlore phase and signature of field induced spin ice ground state in Dy$_{2-x}$La$_{x}$Zr$_{2}$O$_{7}$; x = 0, 0.15, 0.3

The pyrochlore oxides Dy$_{2}$Ti$_{2}$O$_{7}$ and Ho$_{2}$Ti$_{2}$O$_{7}$ are well studied spin ice systems and have shown the evidences of magnetic monopole excitations. Unlike these, Dy$_{2}$Zr$_{2}$O$_{7}$ is reported to crystallize in a distorted fluorite structure. We present here the magnetic and heat capacity studies of La substituted Dy$_{2}$Zr$_{2}$O$_{7}$. Our findings suggest the absence of spin ice state in Dy$_{2}$Zr$_{2}$O$_{7}$ but the emergence of the magnetic field induced spin freezing near T $\approx$ 10 K in ac susceptibility measurements which is similar to Dy$_{2}$Ti$_{2}$O$_{7}$. The magnetic heat capacity of Dy$_{2}$Zr$_{2}$O$_{7}$ shows a shift in the peak position from 1.2 K in zero field to higher temperatures in the magnetic field, with the corresponding decrease in the magnetic entropy. The low temperature magnetic entropy at 5 kOe field is Rln2 - (1/2)Rln(3/2) which is same as for the spin ice state. Substitution of non-magnetic, isovalent La$^{3+}$ for Dy$^{3+}$ gradually induces the structural change from highly disordered fluorite to weakly ordered pyrochlore phase. The La$^{3+}$ substituted compounds with less distorted pyrochlore phase show the spin freezing at lower field which strengthens further on the application of magnetic field. Our results suggest that the spin ice state can be stabilized in Dy$_{2}$Zr$_{2}$O$_{7}$ either by slowing down of the spin dynamics or by strengthening the pyrochlore phase by suitable substitution in the system.

cond-mat.str-el↗

arXiv2020

Successive spin reorientation and rare earth ordering in Nd$_{0.5}$Dy$_{0.5}$FeO$_{3}$: Experimental and $Ab$-$initio$ investigations

In present study, the magnetic structure and spin reorientation of mixed doped orthoferrite Nd$_{0.5}$Dy$_{0.5}$FeO$_3$ have been investigated. Similar to both parent compounds (NdFeO$_3$ and DyFeO$_3$), the magnetic structure of Fe$^{3+}$ belongs to $Γ_{4}$ irreducible representation (G$_{x}$, F$_{z}$) at room temperature. The experimental measurements confirmed the spin reorientation where magnetic structure of Fe$^{3+}$ changes from $Γ_{4}$ to $Γ_{2}$(F$_{x}$, G$_{z}$) between 75 and 20 \,K while maintaining G-type configuration. Such a gradual spin reorientation is unusual since the large single ion anisotropy of Dy$^{3+}$ ions causes an abrupt $Γ_{4}$${\rightarrow}$ $Γ_{1}$(G$_{y}$) spin reorientation in DyFeO$_3$. Between 20 and 10 \,K, the Fe$^{3+}$ magnetic structure is represented by $Γ_{2}$ (F$_{x}$, G$_{z}$). Unexpectedly, magnetic structure of Fe$^{3+}$ with $Γ_{4}$ representation re-emerges below 10\,K which also coincides with the development of rare-earth (Nd$^{3+}$/Dy$^{3+}$) magnetic ordering having C$_{y}$ configuration with magnetic moment of 1.8 $μ_{B}$. The absence of any signature of second order phase transition in the specific heat confirms the role of $R$(Nd$^{3+}$/Dy$^{3+}$)-Fe$^{3+}$ exchange interaction in the observed "rare-earth ordering" unlike DyFeO$_3$ where Dy$^{3+}$ ordering takes place independently to the magnetic ordering of Fe$^{3+}$ magnetic structure. Our (DFT+U+SO) calculations show that the C-type arrangement of rare-earth ions (Nd$^{3+}$/Dy$^{3+}$) with $Γ_{2}$ configuration for Fe$^{3+}$ moments is the ground state whereas $Γ_{4}$ phase is energetically very close. Nd-Fe and Nd-Dy exchange interactions, estimated from DFT, are observed to have significant roles in the rare earth ordering and Fe spin reorientation corroborating our experimental results.

cond-mat.str-el↗

arXiv2019

Existence of a critical canting angle of magnetic moments to induce multiferroicity in the Haldane spin-chain system, Tb2BaNiO5

We report an unusual canted magnetism due to 3d and 4f electrons, occupying two different crystallographic sites, with its consequence to electric dipole order. This is based on neutron powder diffraction measurements on Tb2BaNiO5 (orthorhombic, Immm centrosymmetric space group), exhibiting Neel order below (TN) 63 K, to understand multiferroic behavior below 25 K. The magnetic structure is made up of Ni and Tb magnetic moments, which are found to be mutually canted in the entire temperature range below TN, though collinearity is seen within each sublattice, as known in the past. First-principles density functional theory calculations (GCA plus SO and GCA plus U plus SO approximations) support such a canted ground state. The intriguing finding, being reported here, is that there is a sudden increase in this Tb-Ni relative cantingle angle at the temperature (that is, at 25 K) at which spontaneous electric polarization sets in, with bond distance and bong angle anomalies. This finding emphasizes the need for a new spin-driven polarization mechanism, that is, a critical canting angle coupled with exchangestriction, to induce multiferroicity in magnetic insulators with canted spins.

cond-mat.str-el↗