arXiv subjects

K. R. Priolkar

Publications and source records attributed to K. R. Priolkar.

At least 19 recordsLinked to original sources

arXiv2022

Antisite disorder and phase segregation in Mn$_{2}$NiSn

A systematic study of crystal structure, local structure, magnetic and transport properties in quenched and temper annealed Ni$_{2-x}$Mn$_{1+x}$Sn alloys indicate the formation of Mn$_3$Sn type structural defects caused by an antisite disorder between Mn and Sn occupying the Y and Z sublattices of X$_2$YZ Heusler structure. The antisite disorder is caused by the substitution of Ni by Mn at the X sites. On temper annealing, these defects segregate and phase separate into $L2_1$ Heusler and $D0_{19}$ Mn$_3$Sn type phases.

cond-mat.mtrl-sci↗

arXiv2021

Randomly packed Ni$_2$MnIn and NiMn structural units in off stoichiometric Ni$_2$Mn$_{2-y}$In$_y$ alloys

Ni$_2$Mn$_{2-y}$In$_y$ alloys transform from the martensitic $L1_0$ antiferromagnetic ground state near $y = 0$ to austenitic ferromagnetic $L2_1$ Heusler phase near $y = 1$ due to doping of In impurity for Mn. The off stoichiometric alloys prepared by rapid quenching are structurally metastable and dissociate into a mixture of $L2_1$ (Ni$_2$MnIn) and $L1_0$ (NiMn) phases upon temper annealing. Despite this structural disintegration, the martensitic transformation temperature remains invariant in the temper annealed alloys. Investigations of the local structure of the constituent atoms reveal the presence of strongly coupled Ni$_2$MnIn and NiMn structural units in the temper annealed as well as the rapidly quenched off stoichiometric Ni$_2$Mn$_{2-y}$In$_y$ alloys irrespective of their crystal structure. This random packing of the $L2_1$ and $L1_0$ structural units seems to be responsible for invariance of martensitic transition temperature in the temper annealed alloys as well as the absence of strain glass transition in rapidly quenched alloys.

cond-mat.mtrl-sci↗

arXiv2021

Structural defects responsible for strain glassy transition in Ni$_{50+x}$Ti$_{50-x}$

The strain glassy phase is produced by doping a small percentage of impurity in a martensitic alloy. Its ground state is conceived to consist of martensitic nano domains spatially separated from each other by a defect phase. The present study, by probing the local structure around the Ni and Ti in martensitic and strain glassy compositions of Ni$_{50+x}$Ti$_{50-x}$, for the first time, identifies the defect phase that is responsible for inhibiting the long range ordering of the elastic strain vector leading to the formation of the strain glassy phase.

cond-mat.mtrl-sci↗

arXiv2021

Strain glass versus antisite disorder induced ferromagnetic state in Fe doped Ni-Mn-In Heusler martensites

Fe doping in Ni$_2$Mn$_{1.5}$In$_{0.5}$ results in suppression of the martensitic phase via two contrasting routes. In Ni$_2$Mn$_{1.5-x}$Fe$_{x}$In$_{0.5}$, the martensitic phase is converted to a strain glassy phase, while in Ni$_{2-y}$Fe$_y$Mn$_{1.5}$In$_{0.5}$, a cubic ferromagnetic phase results at the expense of the martensite. Careful studies of magnetic and structural properties reveal the presence of the impurity $γ-$(Fe,Ni) phase as the reason for the emergence of non-ergodic strain glassy phase when Fe is sought to be doped at Y/Z (Mn) sites of X$_2$YZ Heusler alloy. Whereas attempts to dope Fe in the X (Ni) sublattice result in an A2 type antisite disorder that promotes a ferromagnetic ground state.

cond-mat.mtrl-sci↗

arXiv2020

Lattice strain accommodation and absence of pre-transition phases in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$

The stoichiometric Ni$_{50}$Mn$_{25}$In$_{25}$ Heusler alloy transforms from a stable ferromagnetic austenitic ground state to an incommensurate modulated martensitic ground state with a progressive replacement of In with Mn without any pre-transition phases. The absence of pre-transition phases like strain glass in Ni$_{50}$Mn$_{25+x}$In$_{25-x}$ alloys is explained to be the ability of the ferromagnetic cubic structure to accommodate the lattice strain caused by atomic size differences of In and Mn atoms. Beyond the critical value of $x$ = 8.75, the alloys undergo martensitic transformation despite the formation of ferromagnetic and antiferromagnetic clusters and the appearance of a super spin glass state.

cond-mat.mtrl-sci↗

arXiv2020

$d$ band filling and magnetic phase separation in transition metal-doped Mn$_3$SnC

The structural and magnetic properties of transition metal-doped Mn$_3$SnC are studied with an aim to understand the effect of transition metal atom on magnetostructural properties of the antiperovskite compound. The doped Mn$_{2.8}$T$_{0.2}$SnC (T = Cr, Fe, Co, Ni and Cu) compounds show a distinctly different magnetic behavior which can be related to electronic filling of the $d$ band of the transition metal atom. While Cr and Fe doped Mn$_3$SnC show properties similar to that of Mn$_3$SnC, the Co, Ni and Cu doped compounds exhibit nucleation of secondary phases which are devoid of carbon and having Heusler and DO19 type hexagonal structure. A strong magnetic interaction is observed between the impurity phases and the major antiperovskite phase leading to a sharp decrease in magnetostructural transition temperature of the antiperovskite phase and a cluster glassy ground state.

cond-mat.mtrl-sci↗

arXiv2020

Importance of site occupancy and absence of strain glassy phase in Ni$_{2-x}$Fe$_{x}$Mn$_{1.5}$In$_{0.5}$

Martensitic transition temperature steadily decreases in Ni$_{2-x}$Fe$_{x}$Mn$_{1.5}$In$_{0.5}$ and is completely suppressed at $x$ = 0.2. Despite suppression of martensitic transition, Ni$_{1.8}$Fe$_{0.2}$Mn$_{1.5}$In$_{0.5}$ does not display the expected strain glassy phase. Instead, a ground state with dominant ferromagnetic interactions is observed. A study of structural and magnetic properties of $x$ = 0.2 reveal that the alloy consists of a major Fe rich cubic phase and a minor Fe deficient monoclinic phase favoring a ferromagnetic ground state. This is exactly opposite of that observed in Ni$_2$Mn$_{1-y}$Fe$_{y}$In$_{0.5}$ wherein a strain glassy phase is observed for $y$ = 0.1. The change in site symmetry of Fe when doped for Ni in contrast to Mn in the Heusler composition seems to support the growth of the ferromagnetic phase.

cond-mat.mtrl-sci↗

arXiv2020

Modulations in magnetostructural coupling in C and Sn deficient Mn$_3$SnC

The structural and magnetic interactions in stoichiometric (Mn$_3$SnC), carbon deficient (Mn$_3$SnC$_{0.8}$) and tin deficient (Mn$_3$Sn$_{0.85}$C) antiperovskite compounds are studied using x-ray absorption fine structure spectroscopy and neutron diffraction. The study confirms the presence of local structural distortions only around Mn atoms in the antiperovskite compounds irrespective of their stoichiometry. The distortions in the Mn$_6$C octahedra are such that only Mn atoms are displaced from their crystallographic positions resulting in long and short Mn-Mn bonds. These long and short Mn-Mn bonds are responsible for presence of ferromagnetic and antiferromagnetic moments on Mn atoms. The C deficiency at the center of the octahedra increases the strain on the Mn$_6$C octahedra and results in a wide variation of Mn-Mn bond distances as a function of temperature and large hysteresis in magnetic properties. On the other hand, Sn deficiency tends to relax strain by giving more space for the octahedra to distort leading to temperature independent Mn-Mn bond distances.

cond-mat.mtrl-sci↗

arXiv2020

Packing fraction related distortion of Mn$_6$C octahedra and its effect on the first order magnetic transition in Mn based antiperovskites

In this paper, we attempt to understand the cause of magnetostructural transformation in Mn-based antiperovskites by calculating EXAFS at the K edges of constituent metal atoms in three antiperovskite compounds, Mn$_3$GaC, Mn$_3$SnC and Mn$_3$InC. These three compounds have very different magnetic ground states despite the similar cubic structure. Our calculations show that the distortions of Mn$_6$C octahedra, which are responsible for the first-order magnetic transition to antiferromagnetic state, depends on the packing fraction of the lattice.

cond-mat.mtrl-sci↗

arXiv2019

Absence of first order magnetic transition, a curious case of Mn3InC

The volume expanding magnetostructural transition in Mn$_3$GaC and Mn$_3$SnC has been identified to be due to distortion of Mn$_6$C octahedra. Despite a similar lattice volume as Mn$_3$SnC and similar valence electron contribution to the density of states as in Mn$_3$GaC, Mn$_3$InC does not undergo a first order magnetostructural transformation like the Ga and Sn antiperovskite counterparts. A systematic investigation of its structure and magnetic properties using probes like x-ray diffraction, magnetization measurements, neutron diffraction and extended x-ray absorption fine structure (EXAFS) reveal that though the octahedra are distorted resulting in long and short Mn -- Mn bonds and different magnetic moments on Mn atoms, the interaction between them remains ferromagnetic. This has been attributed to the strain on the Mn$_6$C octahedra produced due to the relatively larger size of In atom compared to Sn and Ga. The size of In atom constricts the deformation of Mn$_6$C octahedra giving rise to Mn -- Mn distances that favor only ferromagnetic interactions in the compound.

cond-mat.mtrl-sci↗

arXiv2018

Role of Tin and Carbon in the magnetic interactions in Mn$_3$SnC

In this paper we attempt to understand the role of tin and carbon in magnetic interactions in Mn$_3$SnC. Mn$_3$SnC exhibits a time dependent magnetic configuration and a complex magnetic ground state with both ferromagnetic and antiferromagnetic orders. Such a magnetic state is attributed to presence of distorted Mn$_6$C octahedra with long and short Mn--Mn bonds. Our studies show that C deficiency increases the tensile strain on the Mn$_6$C octahedra which elongates Mn--Mn bonds and strengthens ferromagnetic interactions while Sn deficiency tends to ease out the strain resulting in shorter as well as longer Mn--Mn bond distances in comparison with stoichiometric Mn$_3$SnC. Such a variation strengthens both, ferromagnetic and antiferromagnetic interactions. Thus the structural strain caused by both Sn and C is responsible for complex magnetic ground state of Mn$_3$SnC.

cond-mat.mtrl-sci↗

arXiv2018

Phase separation and effect of strain on magnetic properties of Mn$_3$Ga$_{1-x}$Sn$_x$C

While the unit cell volume of compounds belonging to the Mn$_3$Ga$_{1-x}$Sn$_x$C, (0 $ \le x \le $ 1) series shows a conformity with Vegard's law, their magnetic and magnetocaloric properties behave differently from those of parent compounds Mn$_3$GaC and Mn$_3$SnC. A correlation between the observed magnetic properties and underlying magnetic and local structure suggests that replacing Ga atoms by larger atoms of Sn results in the formation of Ga-rich and Sn-rich clusters. As a result, even though the long range structure appears to be cubic, Mn atoms find themselves in two different local environments. The packing of these two different local structures into a single global structure induces tensile/compressive strains on the Mn$_{6}$C functional unit and is responsible for the observed magnetic properties across the entire solid solution range.

cond-mat.mtrl-sci↗

arXiv2018

Unusual Strain glassy phase in Fe doped Ni$_2$Mn$_{1.5}$In$_{0.5}$

Fe doped Ni$_2$Mn$_{1.5}$In$_{0.5}$, particularly, Ni$_2$Mn$_{1.4}$Fe$_{0.1}$In$_{0.5}$, despite having an incommensurate, modulated 7M martensitic structure at room temperature exhibits frequency dependent behavior of storage modulus and loss that obeys Vogel-Fulcher law as well as shows ergodicity breaking between zero field cooled and field cooled strain measurements just above the transition temperature. Both, frequency dependence and ergodicity breaking are characteristics of a strain glassy phase and occur due to presence of strain domains which are large enough to present signatures of long range martensitic order in diffraction but are non interacting with other strain domains due to presence of Fe impurity.

cond-mat.mtrl-sci↗

arXiv2018

Role of local structural distortion in driving ferroelectricity in GdCrO3

Temperature dependent synchrotron x-ray diffraction and extended x-ray absorption fine structure (EXAFS) studies were performed to understand the role of structural characteristics in driving the magnetoelectric mul- tiferoic properties of GdCrO3. The results suggest that the distortion in the structure appears to be associated with the off-center displacement of Gd-atoms together with octahedral rotations via displacement of the oxygen ions in GdCrO3. In addition, the magnetic coupling below magnetic transition temperature leads to additional distortion in the system via magnetostriction effect, playing a complementary role in the enhancement of ferro- electric polarization. Further, a comparative EXAFS study of GdCrO3 with a similar system YCrO3 suggests that oxygen environment of Gd in GdCrO3 is different from Y in YCrO3, which resulting in an orthorhombic P na21 structure in GdCrO3 in contrast to the monoclinic P 21 structure in YCrO3 .

cond-mat.mtrl-sci↗

arXiv2017

Mechanism of magnetostructural transformation in multifunctional Mn$_3$GaC

Mn$_3$GaC undergoes a ferromagnetic to antiferromagnetic, volume discontinuous cubic-cubic phase transition as a function of temperature, pressure and magnetic field. Through a series of temperature dependent x-ray absorption fine structure spectroscopy experiments at the Mn K and Ga K edge, it is shown that the first order magnetic transformation in Mn$_3$GaC is entirely due to distortions in Mn sub-lattice and with a very little role for Mn-C interactions. The distortion in Mn sub-lattice results in long and short Mn-Mn bonds with the longer Mn-Mn bonds favoring ferromagnetic interactions and the shorter Mn-Mn bonds favoring antiferromagnetic interactions. At the first order transition, the shorter Mn-Mn bonds exhibit an abrupt decrease in their length resulting in an antiferromagnetic ground state and a strained lattice.

cond-mat.mtrl-sci↗

arXiv2017

Phase separated magnetic ground state in Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C

Existence of non-ergodic ground states is considered as a precursor to a first order long range magnetostructural transformation. Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C lies compositionally between two compounds, Mn$_3$GaC and Mn$_3$SnC, undergoing first order magnetic transformation. Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C though crystallizes in single phase cubic structure, exhibits more than one long range magnetic transitions. Using a combination of magnetization, ac susceptibility, neutron diffraction and XAFS techniques it is shown that, though Mn$_3$Ga$_{0.45}$Sn$_{0.55}$C exhibits long range magnetic order, it presents a cluster glassy ground state due to formation of magnetically ordered Ga rich and Sn rich clusters. The clusters are big enough to present signatures of long range magnetic order but are distributed in such way that it limits interactions between two clusters of the same type leading to a frozen magnetic state at low temperatures. The main reason for such a cluster glass state is the difference in local structure of Mn atoms that find themselves in Ga rich and Sn rich clusters.

cond-mat.mtrl-sci↗

arXiv2017

Effect of site occupancy disorder on Martensitic properties of Mn$_{2}$NiIn type alloys: x-ray absorption fine structure study

We have carried out \textit{ab-initio} calculations of local structure of Mn and Ni in Mn$_{2}$Ni$_{1.5}$In$_{0.5}$ alloy with different site occupancies in order to understand the similarities in martensitic and magnetic properties of Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ and Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Our results show that in Mn$_{2}$Ni$_{1+x}$In$_{1-x}$ alloys there is a strong possibility of Mn atoms occupying all the three, X, Y and Z sites of X$_2$YZ Heusler structure while Ni atoms preferentially occupy the X sites. Such a site occupancy disorder of Mn atoms is in addition to a local structural disorder due to size differences between Mn and In atoms which is also present in Ni$_2$Mn$_{1+x}$In$_{1-x}$ alloys. Further, a comparison of the calculations with experimental XAFS at the Mn and Ni K edges in Mn$_{2-y}$Ni$_{1.6+y}$In$_{0.4}$ ($-0.08 \le y \le 0.08$) indicate a strong connection between martensitic transformation and occupancy of Z sites by Mn atoms.

cond-mat.mtrl-sci↗

arXiv2017

Evolution of structure, magnetic and transport properties of Fe$_{1-x}$Mn$_{x}$Se

The present paper seeks to investigate effect of Mn doping in superconducting FeSe. It is found that over the entire doping range in Fe$_{1-x}$Mn$_x$Se ($0 \le x \le 1$), Mn does not substitute Fe in the superconducting tetragonal phase. Instead two impurity phases, NiAs type hexagonal phase and NaCl type cubic phase grow with increasing Mn content. Initially, hexagonal phase has a higher content than the cubic phase but beyond $x$ = 0.5, the cubic phase grows rapidly and for $x \ge 0.8$, the sample is monophasic with cubic NaCl type structure. The superconducting tetragonal phase content steadily decreases with increasing Mn concentration and completely disappears beyond $x = 0.5$. The premise that Mn never replaces Fe in the superconducting phase is further strengthened by observation of a sharp drop in AC susceptibility akin to superconducting transition at the T$_c$ of FeSe up to $x$ = 0.5. EXAFS studies at the Fe K edge also show that the Fe has a four coordinated tetragonal local structure in all compositions below $x = 0.5$, similar to that in FeSe and it gradually changes to a six coordinated one as is expected for a NaCl type cubic phase for $x \ge 0.5$.

cond-mat.supr-con↗