156 research outputs found
Magnetic and transport behaviors of non-centrosymmetric Nd7Ni2Pd
No full textCrystallographic, magnetic, electrical transport and thermodynamic properties of pseudo-binary Nd7Ni2Pd compound have been studied using temperature-dependent x-ray powder diffraction and physical property measurements. Compared to the ferromagnetic parent Nd7Pd3, the ground state of Nd7Ni2Pd is antiferromagnetic, and it exhibits strong metamagnetism. The measurements indicate two antiferromagnetic transitions in fields less than 8 kOe: a second-order paramagnetic to antiferromagnetic at TN2 = 29 K and a weak first-order antiferromagnetic to antiferromagnetic transition at TN1 = 24.5 K. The compound becomes ferromagnetic in fields of 8 kOe and higher with TC = 30 K. Temperature dependence of lattice parameters is anomalous, most prominently in the basal plane at ∼30 K; however, there is no detectable structural distortion or clear volume discontinuity around 25 K, suggesting a significant weakening of the first-order transition when compared to the binary Nd7Pd3.</p
Magnetic ionic liquids based on transition metal complexes with N-alkylimidazole ligands
No full textIn this study, magnetic ionic liquids (MILs) consisting of Ni(II), Co(II), and Mn(II) and paired with the bis[(trifluoromethyl)sulfonyl]imide [NTf2−] anion were synthesized from their water soluble chloride intermediates. The MILs feature low viscosity, high hydrophobicity, and hydrolytic stability making them attractive candidates for a number of highly interdisciplinary applications.This is a manuscript of an article published as Chand, Deepak, Muhammad Qamar Farooq, Arjun K. Pathak, Jingzhe Li, Emily A. Smith, and Jared L. Anderson. "Magnetic ionic liquids based on transition metal complexes with N-alkylimidazole ligands." New Journal of Chemistry 43, no. 1 (2019): 20-23. DOI: 10.1039/C8NJ05176C. Posted with permission.</p
Origins of magnetic memory and strong exchange bias bordering magnetic compensation in mixed-lanthanide systems
No full textUnexpected physical phenomena resulting from the seemingly inconsequential substitutions of chemically similar lanthanide elements in the Pr1-xGdxScGe system are exploited to further the understanding of rare-earth magnetism and inform materials design. By directly probing magnetic moments of crystallographically indistinguishable Pr and Gd we solve the puzzles of how an unusual magnetic memory and strong exchange bias emerge at specific, easily predictable chemistries. Both effects are rooted in a robust antiparallel arrangement of large 4f magnetic moments of light and heavy lanthanides. This enables precise control of nearly zero net magnetization either opposed to, or aligned with, the external magnetic field that persists over a wide range of temperatures and fields. Further, spontaneous perturbations in the random distribution of lanthanide ions makes strong exchange bias possible in bulk single-phase compounds bordering magnetic compensation, consequently expanding the materials base beyond artificial magnetic multilayers and broadening the range of potential applications of the phenomenon.This article is published as Del Rose, Tyler J., Yaroslav Mudryk, Daniel Haskel, Arjun K. Pathak, and Vitalij K. Pecharsky. "Origins of magnetic memory and strong exchange bias bordering magnetic compensation in mixed-lanthanide systems." Physical Review Materials 6, no. 4 (2022): 044413.
DOI: 10.1103/PhysRevMaterials.6.044413.
Copyright 2022 American Physical Society.
Posted with permission.
DOE Contract Number(s): AC02-06CH11357; AC02-07CH11358
Extraordinarily strong magneto-responsiveness in phase-separated LaFe2Si
No full textMaterials responding vigorously to minor variations of external stimuli with negligible hysteresis could revolutionize many of the energy technologies, including refrigeration, actuation, and sensing. We report a combined experimental and theoretical study of a two-phase composite, naturally formed at the LaFe2Si stoichiometry, which exhibits a nearly anhysteretic, two-step first-order ferromagnetic-to-paramagnetic phase transformation with enhanced sensitivity to an external magnetic field. Other unusual properties include a large plateau-like positive magnetoresistance, magnetic-field-induced temperature and entropy changes occurring over a wide temperature range, and a Griffiths-like phase associated with short-range ferromagnetic clustering in the paramagnetic state. The heat capacity, magnetization, Mössbauer spectroscopy, and electrical resistivity, all exhibit characteristic, unusually sharp, first-order discontinuities even in magnetic fields as high as 100 kOe. We expect that similar phenomena could be designed in other mixed-phase systems, leading to novel functionalities, such as giant caloric effects in many yet undiscovered or/and underperforming intermetallic compounds.This article is published as Pathak, Arjun K., Yaroslav Mudryk, Nikolai A. Zarkevich, Dominic H. Ryan, Duane D. Johnson, and Vitalij K. Pecharsky. "Extraordinarily strong magneto-responsiveness in phase-separated LaFe2Si." Acta Materialia (2021): 117083. DOI: 10.1016/j.actamat.2021.117083. </p
Designed materials with the giant magnetocaloric effect near room temperature
No full textThe coupling between structural and magnetic degrees of freedom is crucial for realization of interesting physical phenomena associated with magneto-structural transformations resembling austenite-to-martensite transitions. Despite substantial efforts in design and discovery of materials with strong magnetocaloric effects, majority of viable candidates are composed of non-earth-abundant and toxic elements, while others involve challenging syntheses and post processing. Guided by advanced density functional theory calculation, we report a new family of compounds, i.e., Mn0.5Fe0.5NiSi1-xAlx [x = 0.045–0.07] exhibiting a giant magnetocaloric effect (MCE) that is tunable near room temperature. Their MCE functionality arises from a distinct magneto-structural transformation between a paramagnetic hexagonal Ni2In-type phase and ferromagnetic orthorhombic TiNiSi-type phase that can be actuated by magnetic field and/or pressure. As the transition is sensitive to external hydrostatic pressure, the same materials should also exhibit a strong barocaloric response in addition to the giant MCE.This is a manuscript of an article published as Biswas, Anis, Arjun K. Pathak, Nikolai A. Zarkevich, Xubo Liu, Yaroslav Mudryk, Viktor Balema, Duane D. Johnson, and Vitalij K. Pecharsky. "Designed materials with the giant magnetocaloric effect near room temperature." Acta Materialia 180 (2019): 341-348. DOI: 10.1016/j.actamat.2019.09.023. Posted with permission.</p
Formation, Stability and Magnetism of New Gd3TAl3Ge2 Quaternary Compounds (T = Mn, Cu)
No full textA study on the formation and stability of new quaternary compounds with the general chemical formula Gd3TAl3Ge2 (T = Mn, Cu) has been undertaken by experimental investigations (SEM-EDX, DTA and XRD) and density functional theory (DFT) calculations. These compounds crystallize in the hexagonal Y3NiAl3Ge2-type structure (hP9, P–62m, Z = 1) (an ordered, quaternary derivative of the ternary ZrNiAl or of the binary Fe2P prototypes), with lattice parameters values a = 7.0239(2) Å and c = 4.2580(1) Å for Gd3MnAl3Ge2 and a = 7.0434(1) Å and c = 4.2089(1) Å for Gd3CuAl3Ge2. DTA suggests a peritectic reaction for the formation of these compounds (at 1245 degrees C for Gd3CuAl3Ge2). The existence and stability of these phases has been explained on the basis of DFT calculations, and a comparison of ground state properties of the studied compounds with the earlier known Gd3CoAl3Ge2 phase is outlined. The negative formation energies in all three cases govern the stability of compounds from theory as well, predicting Gd3MnAl3Ge2 as the most stable phase with highest formation energy (–13.01 eV/f.u.). The total DOS are generic in nature and suggest the robust magnetism, with the Gd-f moments of approximately equal to 7 the Bohr magnetons. An antiparallel coupling among Gd-f and T-d states is observed for all compounds, as usually seen in rare earth (R) - transition metal (T) compounds. Preliminary magnetization measurements on Gd3MnAl3Ge2 show two ferromagnetic/ferrimagnetic (FM/FIM) like transitions at TC1 = 142 K and TC2 = 97 K, with another anomaly seen at approximately equal to15 K. Isothermal magnetization data show no hysteresis even at 5 K, and the magnetization does not saturate up to 50 kOe, further suggesting a possible FIM behavior.</p
First-order magnetic phase transition in Pr2In with negligible thermomagnetic hysteresis
No full textMagnetic first-order phase transitions are key for the emergence of functionalities of fundamental and applied significance, including magnetic shape memory as well as magnetostrictive and magnetocaloric effects. Such transitions are usually associated with thermomagnetic hysteresis. We report the observation of a first-order transition in Pr2In from a paramagnetic to a ferromagnetic state at TC=57K without a detectable thermomagnetic hysteresis, which is also accompanied by a large magnetocaloric effect. The peculiar electronic structure of Pr2In exhibiting a large density of states near the Fermi energy explains the highly responsive magnetic behavior of the material. The magnetic properties of Pr2In are reported, including observation of another (second-order) magnetic transition at 35 K.This article is published as Biswas, Anis, N. A. Zarkevich, Arjun K. Pathak, O. Dolotko, Ihor Z. Hlova, A. V. Smirnov, Y. Mudryk, D. D. Johnson, and V. K. Pecharsky. "First-order magnetic phase transition in Pr2In with negligible thermomagnetic hysteresis." Physical Review B 101, no. 22 (2020): 224402. DOI: 10.1103/PhysRevB.101.224402. Posted with permission.</p
A Method of Transformation for Generalized Hypergeometric Function 2F2
No full textBy employing an addition theorem for the confluent hypergeometric function, Paris R.B.[3], has obtained a Kummer-type transformation for a 2F2 (x) hypergeometric function with general parameters in the form of a sum of 2F2 (-x) functions. Recently, Choi Junesang and Rathie Arjun K.[1], has obtained the same result without using the addition theorem. The aim of this paper is to derive the result of Paris R.B.[3], with change in the general parameters without using the addition theorem in the line of Choi Junesang and Rathie Arjun K.[1]. Corresponding author E.mail:- [email protected], [email protected]
Magnetic and magnetocaloric properties of Gd<sub>6</sub>X<sub>2</sub>Si<sub>3</sub> (X = Ni, Co) and Ln<sub>6</sub>Co<sub>2</sub>Si<sub>3</sub> (Ln = Pr, La)
No full textPhase compositions and crystal structures of Gd6X 2Si3 (X = Ni, Co,) and Ln6Co2Si 3 (Ln = Pr, La) have been studied. The magnetic properties of Gd 6X2Si3 (X = Ni, Co) and Ln6Co 2Si3 (Ln = Pr, La) have been evaluated from magnetization measurements performed by a superconducting quantum interference device magnetometer in a temperature interval of 5-400 K, and at magnetic fields up to 5T. The crystal structures of Gd6X2Si3 (X = Co, Ni) and Ln6Co2Si3 (Ln = Pr, La) were found to be hexagonal at 300 K. The Curie temperature (TC), effective and magnetic moment of the compounds (at5 K) have been determined for Gd 6X2Si3 (X = Ni, Co), and Ln6Co 2Si3 (Ln = Pr, La). TC was found to depend on composition, and reaches maximum value of about 300 K for the Gd 6X2Si3 system. Themagnetocaloric effect (magnetic entropy changes and relative cooling power (RCP) was found to depend on X and Ln, and the maximum RCP values were found to be larger than 500 J/kg near room temperature for the Gd6Ni2Si3 and Gd6Co2Si3 compounds. This value of RCP is comparable to the prototype magnetic refrigeration material, Gd. © 2011 American Institute of Physics
Making augmented human intelligence in medicine practical: A case study of treating major depressive disorder
No full textIndividualized medicine tailors diagnoses and treatment options on an individual patient basis. This is a paradigm shift from choosing a treatment based on highest reported efficacy in clinical trials, which is often not effective for all individuals. In this dissertation, we assert that treatment selection and management can be individualized when clinicians assessment of disease symptoms are augmented with a few analytically identified patient-specific measures (e.g., genomics, metabolomics) that are prognostic or predictive of treatment outcomes. Patient-derived biological, clinical and symptom measures are sufficiently complex, i.e., heterogeneous, noisy and high-dimensional. The question for research then becomes: “Which few among these large complex measures are sufficient to augment the clinician’s disease assessment and treatment logic to individualize treatment decisions?”
This dissertation introduces, ALMOND — Analytics and Machine Learning Framework for Actionable Intelligence from Clinical and Omics Data. As a case study, this dissertation describes how ALMOND addresses the unmet need for individualized medicine in treating major depressive disorder — the leading cause of medical disabilities worldwide. The biggest challenge in individualizing treatment of depression is in the heterogeneity of how depressive symptoms manifest between individuals, and in their varied response to the same treatment.
ALMOND comprises a systematic analytical workflow to individualize antidepressant treatment by addressing the challenge of heterogeneity of major depressive disorder. First, “right patients” are identified by stratifying patients using unsupervised learning, that serves as a foundation to associate their disease states with multiple pharmacological (drug-associated) measures. Second, “right drug” selection is shown to be feasible by demonstrating that psychiatrists’ depression severity assessments augmented with pharmacogenomic measures can accurately predict remission of depressive symptoms using supervised learning. Finally, probabilistic graphs provide early and easily interpretable prognoses at the “right time” to a psychiatrist by accounting for changes in routinely assessed depressive symptoms’ severity. By choosing antidepressants that have the highest-likelihood of the patient achieving remission, the chances of persisting depressive symptoms are reduced, which is often the leading medical conditions in those who commit suicide or develop chronic illnesses.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-05-01The student, Arjun Athreya, accepted the attached license on 2019-04-12 at 15:37.The student, Arjun Athreya, submitted this Dissertation for approval on 2019-04-12 at 15:45.This Dissertation was approved for publication on 2019-04-12 at 16:30.DSpace SAF Submission Ingestion Package generated from Vireo submission #13592 on 2019-08-22 at 15:05:58Made available in DSpace on 2019-08-23T20:35:51Z (GMT). No. of bitstreams: 2
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