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Brar J, Bindu R. Investigation of magnetic exchange interactions in Cr-dopedCa0.5Sr0.5RuO3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2024; 36:325503. [PMID: 38653327 DOI: 10.1088/1361-648x/ad4248] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Accepted: 04/23/2024] [Indexed: 04/25/2024]
Abstract
The value of Curie temperature (TC) and resistivity forCa0.5Sr0.5Ru1-xCrxO3are found to increase with increase inxfrom 0 to 0.1. TheTCincreases from 38 K to 107 K. In this work, we investigate the increment using spin polarised density functional theory. The compounds exhibit Griffiths phase. Our results show that to understand the behaviour of the increase inTC, it is important to consider not only the competing super exchange and super-super exchange interactions between Ru/Cr-Ru/Cr ion pairs but also the increment in the value of the magnetic moment due to the localized character of the dopant (Cr) ion. Our results suggest that the increased resistivity with Cr doping could be due to increased scattering rate and strong on-site coulomb repulsion due to Cr doping. It is also important to note that the behaviour ofTCwith the Ru-O-Ru bond angle is not in line with the functional form reported for ferrites, chromites and some ferromagnetic oxides. We believe that our results will be helpful in further exploring the origin of magnetism and transport on Cr doping in perovskite ruthenates.
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Affiliation(s)
- Jaskirat Brar
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi, Himachal Pradesh 175005, India
| | - R Bindu
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Mandi, Himachal Pradesh 175005, India
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Brar J, Singh S, Kuga K, Sharma P, M B, Takeuchi T, Bindu R. Lattice effects on the physical properties of half-doped perovskite ruthenates. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2023; 35:195402. [PMID: 36867880 DOI: 10.1088/1361-648x/acc15d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2022] [Accepted: 03/03/2023] [Indexed: 06/18/2023]
Abstract
We investigate the unusual phase transitions in SrRuO3and Sr0.5Ca0.5Ru1-xCrxO3(x = 0, 0.05 and 0.1) employing x-ray diffraction, resistivity, magnetic studies and x-ray photoemission spectroscopy. Our results show the compounds undergo a crossover from itinerant ferromagnetism to localized ferromagnetism. The combined studies suggest Ru and Cr be in the 4+ valence state. A Griffith phase and an enhancement in Curie temperature (Tc) from 38 K to 107 K are observed with Cr doping. A shift in the chemical potential towards the valence band is observed with Cr doping. In the metallic samples, interestingly, a direct link between the resistivity and orthorhombic strain is observed. We also observe a connection between orthorhombic strain andTcin all the samples. Detailed studies in this direction will be helpful to choose suitable substrate materials for thin-film/device fabrication and hence manoeuvre its properties. In the non-metallic samples, the resistivity is mainly governed due to disorder, electron-electron correlation effects and a reduction in the number of electrons at the Fermi level. The value of the resistivity for the 5% Cr doped sample suggests semi-metallic behaviour. Understanding its nature in detail using electron spectroscopic techniques could unravel the possibility of its utility in high-mobility transistors at room temperature and its combined property with ferromagnetism will be helpful in making spintronic devices.
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Affiliation(s)
- Jaskirat Brar
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Himachal Pradesh 175005, India
| | - Saurabh Singh
- Toyota Technological Institute, Nagoya, Aichi 468-8511, Japan
- Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - Kentaro Kuga
- Toyota Technological Institute, Nagoya, Aichi 468-8511, Japan
- Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - Priyamedha Sharma
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Himachal Pradesh 175005, India
| | - Bharath M
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Himachal Pradesh 175005, India
| | - Tsunehiro Takeuchi
- Toyota Technological Institute, Nagoya, Aichi 468-8511, Japan
- Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
| | - R Bindu
- School of Physical Sciences, Indian Institute of Technology Mandi, Kamand, Himachal Pradesh 175005, India
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Huang CL, Santiago JM, Svanidze E, Besara T, Siegrist T, Morosan E. Effects of chemical disorder in the itinerant antiferromagnet Ti 1-x V x Au. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:365602. [PMID: 30079890 DOI: 10.1088/1361-648x/aad832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The fragile nature of itinerant magnetism can be exploited using non-thermal parameters to study quantum criticality. The recently discovered quantum critical point (QCP) in the Sc-doped (hole-like doping) itinerant antiferromagnet TiAu (Ti1-x Sc x Au) raised questions about the effects of the crystal and electronic structures on the overall magnetic behavior. In this study, doping with V (electron-like doping) in Ti1-x V x Au introduces chemical disorder which suppresses antiferromagnetic order from [Formula: see text] 36 K for x = 0 down to 10 K for x = 0.15, whereupon a solubility limit is reached. Signatures of non-Fermi-liquid behavior are observed in transport and specific heat measurements similar to Ti1-x Sc x Au, even though Ti1-x V x Au is far from a QCP for the accessible compositions [Formula: see text].
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Affiliation(s)
- C-L Huang
- Department of Physics and Astronomy, Rice University, Houston, TX 77005, United States of America
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Khan N, Sarkar P, Midya A, Mandal P, Mohanty PK. Continuously Varying Critical Exponents Beyond Weak Universality. Sci Rep 2017; 7:45004. [PMID: 28327622 PMCID: PMC5361157 DOI: 10.1038/srep45004] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Accepted: 02/14/2017] [Indexed: 11/09/2022] Open
Abstract
Renormalization group theory does not restrict the form of continuous variation of critical exponents which occurs in presence of a marginal operator. However, the continuous variation of critical exponents, observed in different contexts, usually follows a weak universality scenario where some of the exponents (e.g., β, γ, ν) vary keeping others (e.g., δ, η) fixed. Here we report ferromagnetic phase transition in (Sm1−yNdy)0.52Sr0.48MnO3 (0.5 ≤ y ≤ 1) single crystals where all three exponents β, γ, δ vary with Nd concentration y. Such a variation clearly violates both universality and weak universality hypothesis. We propose a new scaling theory that explains the present experimental results, reduces to the weak universality as a special case, and provides a generic route leading to continuous variation of critical exponents and multi-criticality.
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Affiliation(s)
- N Khan
- CMP Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhan Nagar, Kolkata 700064, India
| | - P Sarkar
- Department of Physics, Serampore College, Serampore 712201, India
| | - A Midya
- CMP Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhan Nagar, Kolkata 700064, India
| | - P Mandal
- CMP Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhan Nagar, Kolkata 700064, India
| | - P K Mohanty
- CMP Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhan Nagar, Kolkata 700064, India
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Anomalous quantum criticality in an itinerant ferromagnet. Nat Commun 2015; 6:8188. [PMID: 26348932 DOI: 10.1038/ncomms9188] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2014] [Accepted: 07/27/2015] [Indexed: 11/08/2022] Open
Abstract
The dynamics of continuous phase transitions is governed by the dynamic scaling exponent relating the correlation length and correlation time. For transitions at finite temperature, thermodynamic critical properties are independent of the dynamic scaling exponent. In contrast, at quantum phase transitions where the transition temperature becomes zero, static and dynamic properties are inherently entangled by virtue of the uncertainty principle. Consequently, thermodynamic scaling equations explicitly contain the dynamic exponent. Here we report on thermodynamic measurements (as a function of temperature and magnetic field) for the itinerant ferromagnet Sr1-xCaxRuO3 where the transition temperature becomes zero for x=0.7. We find dynamic scaling of the magnetization and specific heat with highly unusual quantum critical dynamics. We observe a small dynamic scaling exponent of 1.76 strongly deviating from current models of ferromagnetic quantum criticality and likely being governed by strong disorder in conjunction with strong electron-electron coupling.
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Sarkar B, Dalal B, De SK. Correlation among disorder, electronic and magnetic phases of SrRuO3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2015; 27:116002. [PMID: 25721450 DOI: 10.1088/0953-8984/27/11/116002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Electric and magnetic properties of Sr1-xBaxRu1-xTixO3 (0 ⩽ x ⩽ 0.8) have been investigated to find the interrelationship between metallicity and ferromagnetism in SrRuO3 (SRO). The simultaneous doping of Sr and Ru with Ba and Ti results in single phase SRO at x = 0.1 and mixed phase of SRO and hexagonal BaTiO3 (h-BTO) at x ⩾ 0.2. Co-doping at Sr and Ru sites gives rise to oxygen vacancy and mixed valency of Ru (Ru(3+) and Ru(4+)). Room temperature resistivity increases due to modification of p(O)-d(Ru) hybridization and phase segregation. Temperature dependent resistivity reveals metal-insulator transition around 232 K at x = 0.1 and insulator down to 2 K at x ⩾ 0.2. The insulating state (x = 0.1) at low temperature is well described by weak localization and electron-electron interaction. Temperature dependence of resistivity (x ⩾ 0.2) follows Mott's three dimensional variable range hopping model. Localization length and average hopping distance decrease with the increase of x, indicating the presence of more disorder. Ferromagnetic transition temperature decreases to 149 K at x = 0.1 and remains constant up to x = 0.5. The Curie-Wiess (CW) temperature (ΘCW) decreases monotonically and becomes negative at x = 0.5. The effective magnetic moment estimated from CW law is smaller than that of pure SRO due to the formation of Ru(3+) ions. The saturation magnetization diminishes, suggesting the demagnetization factor owing to diamagnetic h-BTO. The coercivity increases from 6700 Oe (x = 0) to 12 500 Oe (x = 0.4) and then decreases to 3700 Oe (x = 0.5). Ferromagnetic cluster comprising of doped SRO gives rise to the formation of a Griffith-like phase. The co-occurrence of high jump in resistivity ratio and disappearance of ferromagnetism suggests an interplay between transport process and magnetism at low temperature.
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Affiliation(s)
- Babusona Sarkar
- Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India
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Ibrahim AK, Barghathi H, Vojta T. Enhanced rare-region effects in the contact process with long-range correlated disorder. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:042132. [PMID: 25375463 DOI: 10.1103/physreve.90.042132] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2014] [Indexed: 06/04/2023]
Abstract
We investigate the nonequilibrium phase transition in the disordered contact process in the presence of long-range spatial disorder correlations. These correlations greatly increase the probability for finding rare regions that are locally in the active phase while the bulk system is still in the inactive phase. Specifically, if the correlations decay as a power of the distance, the rare-region probability is a stretched exponential of the rare-region size rather than a simple exponential as is the case for uncorrelated disorder. As a result, the Griffiths singularities are enhanced and take a non-power-law form. The critical point itself is of infinite-randomness type but with critical exponent values that differ from the uncorrelated case. We report large-scale Monte Carlo simulations that verify and illustrate our theory. We also discuss generalizations to higher dimensions and applications to other systems such as the random transverse-field Ising model, itinerant magnets, and the superconductor-metal transition.
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Affiliation(s)
- Ahmed K Ibrahim
- Department of Physics, Missouri University of Science and Technology, Rolla, Missouri 65409, USA
| | - Hatem Barghathi
- Department of Physics, Missouri University of Science and Technology, Rolla, Missouri 65409, USA
| | - Thomas Vojta
- Department of Physics, Missouri University of Science and Technology, Rolla, Missouri 65409, USA
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Vojta T. Strong-disorder magnetic quantum phase transitions: Status and new developments. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/1742-6596/529/1/012016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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