Akhilesh Kumar Patel | IIT Bombay (original) (raw)
Papers by Akhilesh Kumar Patel
Non-collinear antiferromagnetism to compensated ferrimagnetism in Ti(Fe1−xCox)2 (x = 0, 0.5 and 1) alloys: experiment and theory
Physical Chemistry Chemical Physics
The manifestation of the structural and magnetic properties of Co substituted TiFe2 is investigat... more The manifestation of the structural and magnetic properties of Co substituted TiFe2 is investigated using powder X-ray diffraction, magnetization and density functional theory calculations.
Fizika tverdogo tela, 2022
Представлены результаты исследования электронной структуры и оптических свойств интерметаллически... more Представлены результаты исследования электронной структуры и оптических свойств интерметаллических соединений Gd5Sb 3 и Gd5Ge 2 Sb. В приближении локальной электронной плотности с поправкой на сильные электронные взаимодействия в 4 f-оболочке редкоземельного иона (метод DFT + U + SO) проведены расчеты зонного спектра. В широком интервале длин волн методом эллипсометрии измерены оптические постоянные данных материалов, определены энергетические зависимости ряда спектральных параметров. Природа квантового поглощения света обсуждается на основе сравнительного анализа экспериментальных и теоретических спектров межзонной оптической проводимости. Ключевые слова: соединения Gd5Sb 3 Gd5Ge 2 Sb, оптические свойства, электронная структура.
Magnetism and transport behavior of Ni42Co8Mn38Sb12: Magnetization, electrical resistivity and Hall effect measurements
Materials Research Bulletin, 2021
Physical Review B, 2021
We report the results of experimental investigations on structural, magnetic, resistivity, calori... more We report the results of experimental investigations on structural, magnetic, resistivity, caloric properties of Fe2RhZ (Z=Si,Ge) along with ab-initio band structure calculations using first principle simulations. Both these alloys are found to crystallize in inverse Heusler structure but with disorder in tetrahedral sites between Fe and Rh. Fe2RhSi has saturation moment of 5.00 µB and while its counterpart has 5.19 µB. Resistivity measurement reveals metallic nature in both of them. Theoretical simulations using generalized gradient approximation(GGA) predict inverse Heusler structure with ferromagnetic ordering as ground state for both the alloys. However it underestimates the experimentally observed moments. GGA+U approach, with Hubbard U values estimated from density functional perturbation theory helps to improve the comparison of the experimental results. Fe2RhSi is found to be half metallic ferromagnet while Fe2RhGe is not. Varying U values on Fe and Rh sites does not change the net moment much in Fe2RhSi, unlike in Fe2RhGe. Relatively small exchange splitting of orbitals in Fe2RhGe compared to that of Fe2RhSi is the reason for not opening the band gap in the minority spin channel in the former. High ordering temperature and moment make Fe2RhSi useful for spintronics applications.
Materials Research Bulletin, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Magnetism of 3d and 4d doped Mn0.7T0.3NiGe (T = Fe, Co, Ru and Rh): Bulk magnetization and ab initio calculations
Journal of Physics: Condensed Matter, 2019
We compare the magnetic properties of 3<i>d</i> (Fe and Co) and 4<i>d</i>... more We compare the magnetic properties of 3<i>d</i> (Fe and Co) and 4<i>d</i> (Ru and Rh) transition metals doped MnNiGe using the combined results of magnetization and ab-initio calculations. The alloys crystallize in austenite Ni<sub>2</sub>In-type hexagonal phase (space group: P6<sub>3</sub>/mmc) with insignificant difference in the lattice parameters. Mn<sub>0.7</sub>Fe<sub>0.3</sub>NiGe and Mn<sub>0.7</sub>Co<sub>0.3</sub>NiGe exhibit spin-glass behavior, resulting from the competing ferro- and antiferromagnetic interactions. These alloys exhibit spontaneous exchange bias field of about H<sub>SEB</sub> ∼ 110 Oe and 323 Oe. From the 4<i>d</i>-metal doped alloys, Mn<sub>0.7</sub>Ru<sub>0.3</sub>NiGe shows glassy behavior while long-range ferromagnetic order is confirmed in Mn<sub>0.7</sub>Rh<sub>0.3</sub>NiGe. In Mn<sub>0.7</sub>Rh<sub>0.3</sub>NiGe, in agreement with experiment and the theoretical calculations, the ground state is confirmed to be ferromagnetic because of the FM exchange interactions of the Mn magnetic moments. But in Mn<sub>1-x</sub>(Fe,Co,Ru)<sub>x</sub>NiGe alloys the calculations revealed the competing and comparable FM and AFM exchange interaction parameters, resulting in the formation of spin-glassy characteristics.
Journal of Alloys and Compounds, 2019
We report on the magnetic behaviour and electronic structure of partly Sb doped Gd5Ge3 i.e., Gd5G... more We report on the magnetic behaviour and electronic structure of partly Sb doped Gd5Ge3 i.e., Gd5Ge2Sb. The compound crystallizes in Mn5Si3-type hexagonal structure with P63/mcm space group. Strong ferromagnetic exchange correlations in the compound can be inferred from the large positive Weiss temperature θW = 143 K. A weak Griffiths phase at TG ∼ 213 K, which sustains up to a field of 5 kOe, is observed. Multiple magnetic transitions are observed below 200 K with a strong antiferromagnetic character. The increase of magnetization with a reduction in temperature below Néel temperature (TN ∼ 136 K), indicates the non-collinear magnetic structure, which is gradually modified to collinear structure in high fields. An incomplete magnetic-field induced transition is discernible from the isothermal magnetization curves. A large electronic coefficient of specific heat γ reveals the metallic behaviour of the compound. The electronic structure was obtained within the GGA+U method accounting for strong correlations in 4f shell of Gd ions. An antiferromagnetic ordering of Gd magnetic moments was found in the calculations which is in agreement with the experimental magnetic measurements results.
Magnetization, resistivity, specific heat and ab initio calculations of Gd5Sb3
Journal of Physics: Condensed Matter, 2018
We report on the combined results of the structural, magnetic, transport and calorimetric propert... more We report on the combined results of the structural, magnetic, transport and calorimetric properties of Mn5Si3-type hexagonal Gd5Sb3, together with ab initio calculations. It exhibits a ferromagnetic (FM)-like transition at 265 K, antiferromagnetic (AFM) Néel transition at 95.5 K followed by a spin-orientation transition at 62 K. The system is found to be in AFM state down to 2 K in a field of 70 kOe. The FM-AFM phase coexistence is not noticeable despite large positive Curie-Weiss temperature ([Formula: see text] K). Instead, low-temperature AFM and high-temperature FM-like phases are separated in large temperatures. Temperature-magnetic field (H-T) phase diagram reveals field-driven complex magnetic phases. Within the AFM phase, the system is observed to undergo field-driven spin-orientation transitions. Field-induced tricritical and quantum critical points appear to be absent due to the strong AFM nature and by the intervention of FM-like state between paramagnetic and AFM states, respectively. The metallic behavior of the compound is inferred from resistivity along with large Sommerfeld parameter. However, no sign of strong electron-correlations is reasoned from the Kadowaki-Wood's ratio [Formula: see text] [Formula: see text] cm · (mol · K)2(mJ)-2, despite heavy γ. Essentially, ab initio calculations accounting for electronic correlations confirm AFM nature of low-temperature magnetic state in Gd5Sb3 and attainable FM ordering in agreement with experimental data.
Revelation of spin glass behavior in Ru doped MnNiGe: experiment and theory
Journal of Physics: Condensed Matter, 2019
We report on the nature of the magnetism in Ru substituted MnNiGe using the combined results of x... more We report on the nature of the magnetism in Ru substituted MnNiGe using the combined results of x-ray diffraction, dc-magnetization, ac-susceptibility and ab initio calculations. Mn0.7Ru0.3NiGe crystallizes in Ni2In-type hexagonal structure (P63/mmc) at room temperature with lattice parameters a = b = 4.099 [Formula: see text] and c = 5.367 [Formula: see text]. From the dc-magnetization; a broad peak around 46.55 K, separation between zero-field cooled and field-cooled warming state and non-saturating isothermal magnetization with typical S-type hysteresis indicate glassy behavior. A cusp in [Formula: see text] is observed to shift toward high temperatures with increasing frequency. Mydosh parameter ([Formula: see text]), single-relaxation time ([Formula: see text] s) obtained through critical slowing-down analysis, [Formula: see text] from the Vogel-Fulcher law and Tholence criterion [Formula: see text], confirm that Mn0.7Ru0.3NiGe belongs to the short-range interaction spin-glass systems with strong coupling between the magnetic clusters. LSDA+U calculations confirmed the competing exchange interactions between large magnetic moments of the Mn ions in Mn0.7Ru0.3NiGe compound resulting in the formation of spin-glassy characteristics.
Journal of Alloys and Compounds, 2019
We report on the structural, magnetic and transport properties of Ru doped Ni50−xRuxMn38Sb12 (x =... more We report on the structural, magnetic and transport properties of Ru doped Ni50−xRuxMn38Sb12 (x = 0, 3 and 4) alloys. The alloys are found to crystallize in orthorhombic phase for x = 0, orthorhombic plus cubic phase for x = 3 and purely cubic for x = 4 respectively, at room temperature. Extended x-ray absorption fine structure (EXAFS) spectroscopy confirms the orthorhombic and cubic structure for x = 0 and 4 respectively while x = 3 shows mixed austenite and martensite phases, at room temperature. Temperature dependent EXAFS data confirms, first order structural transition from cubic austenite phase to orthorhombic martensite phase occurs at 305 and 265 K for x = 3 and 4 respectively, upon cooling. This is in addition to the second order magnetic phase transition at 350, 330 and 326 K for x = 0, 3 and 4 respectively. The change in the magnetic entropy around the martensitic transition is found to be about 19.5 and 12.3 Jkg −1 K −1 for x = 3 and 4, while it is 7.0 Jkg −1 K −1 for x = 0. These values (for x = 3 and 4) are large when compared to Ni50Mn38Sb12 (7Jkg −1 K −1). Exchange bias field is found to be 383, 362 and 240 Oe at 3 K for x = 0, 3 and 4 respectively. Temperature dependent resistivity of the alloys also confirms the first order phase transition. Magnetoresistance is found to be 9.0 % for x = 3, 3.5 % for x = 4 and 6.0 % for x = 0 respectively near martensite transition. Large resistivity difference between martensitic and austenite phases is due to the difference in the carrier concentration by at least one order. Anomalous Hall contribution ρ AHE xy distinguishes martensite and austenite phases.
Non-collinear antiferromagnetism to compensated ferrimagnetism in Ti(Fe1−xCox)2 (x = 0, 0.5 and 1) alloys: experiment and theory
Physical Chemistry Chemical Physics
The manifestation of the structural and magnetic properties of Co substituted TiFe2 is investigat... more The manifestation of the structural and magnetic properties of Co substituted TiFe2 is investigated using powder X-ray diffraction, magnetization and density functional theory calculations.
Fizika tverdogo tela, 2022
Представлены результаты исследования электронной структуры и оптических свойств интерметаллически... more Представлены результаты исследования электронной структуры и оптических свойств интерметаллических соединений Gd5Sb 3 и Gd5Ge 2 Sb. В приближении локальной электронной плотности с поправкой на сильные электронные взаимодействия в 4 f-оболочке редкоземельного иона (метод DFT + U + SO) проведены расчеты зонного спектра. В широком интервале длин волн методом эллипсометрии измерены оптические постоянные данных материалов, определены энергетические зависимости ряда спектральных параметров. Природа квантового поглощения света обсуждается на основе сравнительного анализа экспериментальных и теоретических спектров межзонной оптической проводимости. Ключевые слова: соединения Gd5Sb 3 Gd5Ge 2 Sb, оптические свойства, электронная структура.
Magnetism and transport behavior of Ni42Co8Mn38Sb12: Magnetization, electrical resistivity and Hall effect measurements
Materials Research Bulletin, 2021
Physical Review B, 2021
We report the results of experimental investigations on structural, magnetic, resistivity, calori... more We report the results of experimental investigations on structural, magnetic, resistivity, caloric properties of Fe2RhZ (Z=Si,Ge) along with ab-initio band structure calculations using first principle simulations. Both these alloys are found to crystallize in inverse Heusler structure but with disorder in tetrahedral sites between Fe and Rh. Fe2RhSi has saturation moment of 5.00 µB and while its counterpart has 5.19 µB. Resistivity measurement reveals metallic nature in both of them. Theoretical simulations using generalized gradient approximation(GGA) predict inverse Heusler structure with ferromagnetic ordering as ground state for both the alloys. However it underestimates the experimentally observed moments. GGA+U approach, with Hubbard U values estimated from density functional perturbation theory helps to improve the comparison of the experimental results. Fe2RhSi is found to be half metallic ferromagnet while Fe2RhGe is not. Varying U values on Fe and Rh sites does not change the net moment much in Fe2RhSi, unlike in Fe2RhGe. Relatively small exchange splitting of orbitals in Fe2RhGe compared to that of Fe2RhSi is the reason for not opening the band gap in the minority spin channel in the former. High ordering temperature and moment make Fe2RhSi useful for spintronics applications.
Materials Research Bulletin, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Magnetism of 3d and 4d doped Mn0.7T0.3NiGe (T = Fe, Co, Ru and Rh): Bulk magnetization and ab initio calculations
Journal of Physics: Condensed Matter, 2019
We compare the magnetic properties of 3<i>d</i> (Fe and Co) and 4<i>d</i>... more We compare the magnetic properties of 3<i>d</i> (Fe and Co) and 4<i>d</i> (Ru and Rh) transition metals doped MnNiGe using the combined results of magnetization and ab-initio calculations. The alloys crystallize in austenite Ni<sub>2</sub>In-type hexagonal phase (space group: P6<sub>3</sub>/mmc) with insignificant difference in the lattice parameters. Mn<sub>0.7</sub>Fe<sub>0.3</sub>NiGe and Mn<sub>0.7</sub>Co<sub>0.3</sub>NiGe exhibit spin-glass behavior, resulting from the competing ferro- and antiferromagnetic interactions. These alloys exhibit spontaneous exchange bias field of about H<sub>SEB</sub> ∼ 110 Oe and 323 Oe. From the 4<i>d</i>-metal doped alloys, Mn<sub>0.7</sub>Ru<sub>0.3</sub>NiGe shows glassy behavior while long-range ferromagnetic order is confirmed in Mn<sub>0.7</sub>Rh<sub>0.3</sub>NiGe. In Mn<sub>0.7</sub>Rh<sub>0.3</sub>NiGe, in agreement with experiment and the theoretical calculations, the ground state is confirmed to be ferromagnetic because of the FM exchange interactions of the Mn magnetic moments. But in Mn<sub>1-x</sub>(Fe,Co,Ru)<sub>x</sub>NiGe alloys the calculations revealed the competing and comparable FM and AFM exchange interaction parameters, resulting in the formation of spin-glassy characteristics.
Journal of Alloys and Compounds, 2019
We report on the magnetic behaviour and electronic structure of partly Sb doped Gd5Ge3 i.e., Gd5G... more We report on the magnetic behaviour and electronic structure of partly Sb doped Gd5Ge3 i.e., Gd5Ge2Sb. The compound crystallizes in Mn5Si3-type hexagonal structure with P63/mcm space group. Strong ferromagnetic exchange correlations in the compound can be inferred from the large positive Weiss temperature θW = 143 K. A weak Griffiths phase at TG ∼ 213 K, which sustains up to a field of 5 kOe, is observed. Multiple magnetic transitions are observed below 200 K with a strong antiferromagnetic character. The increase of magnetization with a reduction in temperature below Néel temperature (TN ∼ 136 K), indicates the non-collinear magnetic structure, which is gradually modified to collinear structure in high fields. An incomplete magnetic-field induced transition is discernible from the isothermal magnetization curves. A large electronic coefficient of specific heat γ reveals the metallic behaviour of the compound. The electronic structure was obtained within the GGA+U method accounting for strong correlations in 4f shell of Gd ions. An antiferromagnetic ordering of Gd magnetic moments was found in the calculations which is in agreement with the experimental magnetic measurements results.
Magnetization, resistivity, specific heat and ab initio calculations of Gd5Sb3
Journal of Physics: Condensed Matter, 2018
We report on the combined results of the structural, magnetic, transport and calorimetric propert... more We report on the combined results of the structural, magnetic, transport and calorimetric properties of Mn5Si3-type hexagonal Gd5Sb3, together with ab initio calculations. It exhibits a ferromagnetic (FM)-like transition at 265 K, antiferromagnetic (AFM) Néel transition at 95.5 K followed by a spin-orientation transition at 62 K. The system is found to be in AFM state down to 2 K in a field of 70 kOe. The FM-AFM phase coexistence is not noticeable despite large positive Curie-Weiss temperature ([Formula: see text] K). Instead, low-temperature AFM and high-temperature FM-like phases are separated in large temperatures. Temperature-magnetic field (H-T) phase diagram reveals field-driven complex magnetic phases. Within the AFM phase, the system is observed to undergo field-driven spin-orientation transitions. Field-induced tricritical and quantum critical points appear to be absent due to the strong AFM nature and by the intervention of FM-like state between paramagnetic and AFM states, respectively. The metallic behavior of the compound is inferred from resistivity along with large Sommerfeld parameter. However, no sign of strong electron-correlations is reasoned from the Kadowaki-Wood's ratio [Formula: see text] [Formula: see text] cm · (mol · K)2(mJ)-2, despite heavy γ. Essentially, ab initio calculations accounting for electronic correlations confirm AFM nature of low-temperature magnetic state in Gd5Sb3 and attainable FM ordering in agreement with experimental data.
Revelation of spin glass behavior in Ru doped MnNiGe: experiment and theory
Journal of Physics: Condensed Matter, 2019
We report on the nature of the magnetism in Ru substituted MnNiGe using the combined results of x... more We report on the nature of the magnetism in Ru substituted MnNiGe using the combined results of x-ray diffraction, dc-magnetization, ac-susceptibility and ab initio calculations. Mn0.7Ru0.3NiGe crystallizes in Ni2In-type hexagonal structure (P63/mmc) at room temperature with lattice parameters a = b = 4.099 [Formula: see text] and c = 5.367 [Formula: see text]. From the dc-magnetization; a broad peak around 46.55 K, separation between zero-field cooled and field-cooled warming state and non-saturating isothermal magnetization with typical S-type hysteresis indicate glassy behavior. A cusp in [Formula: see text] is observed to shift toward high temperatures with increasing frequency. Mydosh parameter ([Formula: see text]), single-relaxation time ([Formula: see text] s) obtained through critical slowing-down analysis, [Formula: see text] from the Vogel-Fulcher law and Tholence criterion [Formula: see text], confirm that Mn0.7Ru0.3NiGe belongs to the short-range interaction spin-glass systems with strong coupling between the magnetic clusters. LSDA+U calculations confirmed the competing exchange interactions between large magnetic moments of the Mn ions in Mn0.7Ru0.3NiGe compound resulting in the formation of spin-glassy characteristics.
Journal of Alloys and Compounds, 2019
We report on the structural, magnetic and transport properties of Ru doped Ni50−xRuxMn38Sb12 (x =... more We report on the structural, magnetic and transport properties of Ru doped Ni50−xRuxMn38Sb12 (x = 0, 3 and 4) alloys. The alloys are found to crystallize in orthorhombic phase for x = 0, orthorhombic plus cubic phase for x = 3 and purely cubic for x = 4 respectively, at room temperature. Extended x-ray absorption fine structure (EXAFS) spectroscopy confirms the orthorhombic and cubic structure for x = 0 and 4 respectively while x = 3 shows mixed austenite and martensite phases, at room temperature. Temperature dependent EXAFS data confirms, first order structural transition from cubic austenite phase to orthorhombic martensite phase occurs at 305 and 265 K for x = 3 and 4 respectively, upon cooling. This is in addition to the second order magnetic phase transition at 350, 330 and 326 K for x = 0, 3 and 4 respectively. The change in the magnetic entropy around the martensitic transition is found to be about 19.5 and 12.3 Jkg −1 K −1 for x = 3 and 4, while it is 7.0 Jkg −1 K −1 for x = 0. These values (for x = 3 and 4) are large when compared to Ni50Mn38Sb12 (7Jkg −1 K −1). Exchange bias field is found to be 383, 362 and 240 Oe at 3 K for x = 0, 3 and 4 respectively. Temperature dependent resistivity of the alloys also confirms the first order phase transition. Magnetoresistance is found to be 9.0 % for x = 3, 3.5 % for x = 4 and 6.0 % for x = 0 respectively near martensite transition. Large resistivity difference between martensitic and austenite phases is due to the difference in the carrier concentration by at least one order. Anomalous Hall contribution ρ AHE xy distinguishes martensite and austenite phases.