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  • 1. Araujo, C. Moyses
    et al.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ramzan, Muhammad
    Shukla, R.
    Jayakumar, O. D.
    Tyagi, A. K.
    Liu, Yi-Sheng
    Chen, Jeng-Lung
    Glans, Per-Anders
    Chang, Chinglin
    Blomqvist, Andreas
    Lizarraga, Raquel
    Holmström, Erik
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Guo, Jinghua
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Disorder-induced Room Temperature Ferromagnetism in Glassy Chromites2014In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 4, p. 4686-Article in journal (Refereed)
    Abstract [en]

    We report an unusual robust ferromagnetic order above room temperature upon amorphization of perovskite [YCrO3] in pulsed laser deposited thin films. This is contrary to the usual expected formation of a spin glass magnetic state in the resulting disordered structure. To understand the underlying physics of this phenomenon, we combine advanced spectroscopic techniques and first-principles calculations. We find that the observed order-disorder transformation is accompanied by an insulator-metal transition arising from a wide distribution of Cr-O-Cr bond angles and the consequent metallization through free carriers. Similar results also found in YbCrO3-films suggest that the observed phenomenon is more general and should, in principle, apply to a wider range of oxide systems. The ability to tailor ferromagnetic order above room temperature in oxide materials opens up many possibilities for novel technological applications of this counter intuitive effect.

  • 2.
    Araujo, C. Moysés
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jun, Xu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jayakumar, Onattu D.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Wu, Yan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Gehring, Gillian A.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Room temperature ferromagnetism in pristine MgO thin films2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23Article in journal (Refereed)
    Abstract [en]

    Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.

  • 3.
    Biswas, Anis
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Shirong, Wang
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Liubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    The effect of oxygen partial pressure during deposition in the magnetic properties of ZnO thin film2011In: Mater Res Soc Symp Proc, 2011, p. 117-122Conference paper (Refereed)
    Abstract [en]

    We have studied the magnetic properties of 100 nm thick ZnO thin films prepared by magnetron sputtering in different oxygen partial pressures (ratio of oxygen pressure to total pressure in deposition chamber, P Oxy). Only the films fabricated at P Oxy below ∼ 0.5 show room temperature ferromagnetism. The saturation magnetization at room temperature is initially found to increase as P Oxy increases and reaches maximum value of ∼ 5 emu/gm at P Oxy ∼ 0.3 and then starts to decrease and becomes diamagnetic for P Oxy &gt; 0.5. From small angle XRD study of structural properties of the films, we find that the lattice stress developed in the film along c-axis also exhibits a similar behavior with the variation of P Oxy. Thus, both the room temperature ferromagnetism and lattice stress appear to originate from the intrinsic defects present in the sample.

  • 4. Chawla, Amit Kumar
    et al.
    Singhal, Sonal
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Gupta, Hari Om
    Chandra, Ramesh
    Study of composition dependent structural, optical, and magnetic properties of Cu-doped Zn1-xCdxS nanoparticles2010In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 12, p. 123519-Article in journal (Refereed)
    Abstract [en]

    Cu-doped Zn1-xCdxS nanoparticles were synthesized by coprecipitation technique in ice bath at 280 K. The band gap energy of Zn1-xCdxS:Cu nanoparticles can be tuned to a lower energy by increasing the Cd content, indicating the formation of the alloyed nanoparticles. The alloy structure is further supported by the systematic shifting of characteristic x-ray diffraction peaks to lower angles with increase in Cd content. Systematic copper doping induces a red shift in the energy band gap of Zn0.9Cd0.1S:Cu nanoparticles with increase in copper concentration. Cu-doped Zn0.9Cd0.1S nanoparticles were found to have ferromagnetic nature at 5 K whereas undoped particles were found to be diamagnetic. Green luminescence further proves proper doping of Cu into the ZnCdS matrix. It is believed that the green luminescence originates from the recombination between the shallow donor level (sulfur vacancy) and the t(2) level of Cu2+. This method provides an inexpensive and simple procedure to produce ternary ZnCdS: Cu nanoparticles with tunable optical properties via changing Cd and/or Cu concentrations.

  • 5. Kaushik, Neelam
    et al.
    Sharma, Parmanand
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kimura, Hisamichi
    Makino, Akihiro
    Inoue, Akihisa
    Exchange-coupled FePtB nano-composite hard magnets produced by pulsed laser deposition2010In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 171, no 1-3, p. 62-68Article in journal (Refereed)
    Abstract [en]

    Nano-composite FePtB thin films were deposited on naturally oxidized (1 0 0) silicon (Si) and glass (SiO2) substrates by using a pulsed laser deposition (PLO) technique. Effects of processing conditions on structural, surface and magnetic properties of the films were examined. Growth temperature (T-s) and the type of substrate (Si or SiO2) are shown to affect crystal structure and magnetic properties of FePtB thin films significantly. Under optimized processing conditions, a similar to 1.7 mu m thick FePtB film deposited on a glass substrate exhibits high coercivity (similar to 7.7 kOe), high reduced remanence [(M-r/M-s) similar to 0.9] and high energy product (BH)(max) = 71 kJ/m(3). The films exhibiting good hard magnetic properties are mainly made-up of nano-sized hard (L1(0)-FePt) and soft (iron-boride) magnetic phases, which are shown to be exchange coupled. Fabrication of hard magnetic thin films by a simple and fast technique such as PLD is very promising for the production of micro magnets for MEMS applications.

  • 6. Moysés Araújo, C.
    et al.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jun, Xu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jayakumar, Onattu D.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wu, Yan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rao, K Venkat.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Unusual ferromagnetism above room temperature in undoped thin films and nanoparticles of MgOManuscript (Other academic)
  • 7. Moysés Araújo, C.
    et al.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    et al.,
    Transformation to Room Temperature Ferromagnetism on Amorphizing Chromite Thin FilmsArticle in journal (Other academic)
    Abstract [en]

    Transformation to Ferromagnetic order above room temperature is observed on amorphizing otherwise antiferromagnetic chromite [Y(Yb)CrO3] thin films produced by pulsed laser deposition.. To understand the underlying physics of this phenomenon, we have combined advanced spectroscopy techniques and first-principles calculations. The amorphization is found to be accompanied by an insulator-metal transition, which in turn affects the magnetic properties. The ferromagnetism (FM) is then explained by evoking a number of coexisting effects, namely disordering of Cr-O-Cr bond angles, metallization which introduces free carriers and the presence of mixed valence states (Cr3+ in the bulk and Cr4+ on the surface). They favor FM coupling through double and direct exchange interactions. Although we have used YCrO3 as case study, our results are more general and must apply for a wide range of oxide systems.

  • 8.
    Nagar, Sandeep
    KTH.
    Beginning julia programming: For engineers and scientists2017Book (Other academic)
    Abstract [en]

    Get started with Julia for engineering and numerical computing, especially data science, machine learning, and scientific computing applications. This book explains how Julia provides the functionality, ease-of-use and intuitive syntax of R, Python, MATLAB, SAS, or Stata combined with the speed, capacity, and performance of C, C++, or Java. You’ll learn the OOP principles required to get you started, then how to do basic mathematics with Julia. Other core functionality of Julia that you’ll cover, includes working with complex numbers, rational and irrational numbers, rings, and fields. Beginning Julia Programming takes you beyond these basics to harness Julia’s powerful features for mathematical functions in Julia, arrays for matrix operations, plotting, and more. Along the way, you also learn how to manage strings, write functions, work with control flows, and carry out I/O to implement and leverage the mathematics needed for your data science and analysis projects. “Julia walks like Python and runs like C”. This phrase explains why Julia is quickly growing as the most favored option for data analytics and numerical computation. After reading and using this book, you’ll have the essential knowledge and skills to build your first Julia-based application. What You’ll Learn Obtain core skills in Julia Apply Julia in engineering and science applications Work with mathematical functions in Julia Use arrays, strings, functions, control flow, and I/O in Julia Carry out plotting and display basic graphics. Who This Book Is For Those who are new to Julia; experienced users may also find this helpful as a reference.

  • 9.
    Nagar, Sandeep
    KTH.
    Introduction to python for engineers and scientists: Open source solutions for numerical computation2017Book (Other academic)
    Abstract [en]

    Familiarize yourself with the basics of Python for engineering and scientific computations using this concise, practical tutorial that is focused on writing code to learn concepts. Introduction to Python is useful for industry engineers, researchers, and students who are looking for open-source solutions for numerical computation. In this book you will learn by doing, avoiding technical jargon, which makes the concepts easy to learn. First you’ll see how to run basic calculations, absorbing technical complexities incrementally as you progress toward advanced topics. Throughout, the language is kept simple to ensure that readers at all levels can grasp the concepts. You will: Understand the fundamentals of the Python programming language Apply Python to numerical computational programming projects in engineering and science Discover the Pythonic way of life Apply data types, operators, and arrays Carry out plotting for visualization Work with functions and loops. 

  • 10.
    Nagar, Sandeep
    KTH.
    Introduction to scilab: For engineers and scientists2017Book (Other academic)
    Abstract [en]

    Familiarize yourself with Scilab using this concise, practical tutorial that is focused on writing code to learn concepts. Starting from the basics, this book covers array-based computing, plotting, and working with files in Scilab. Introduction to Scilab is useful for industry engineers, researchers, and students who are looking for open-source solutions for numerical computation. In this book you will learn by doing, avoiding technical jargon, which makes the concepts easy to learn. First you’ll see how to run basic calculations, absorbing technical complexities incrementally as you progress toward advanced topics. Throughout, the language is kept simple to ensure that readers at all levels can grasp the concepts. After reading this book, you will come away with sample code that can be re-purposed and applied to your own projects using Scilab. Who This Book Is For Engineers, scientists, researchers, and students who are new to Scilab. Some prior programming experience would be helpful but not required.

  • 11.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Multifunctional magnetic materials prepared by Pulsed Laser Deposition2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

         Pulsed LASER deposition (PLD) is widely recognized as excellent deposition technique owing to stoichiometric transfer of target material, easy preparation and high quality. Thin films from few nanometers to micrometer regime can be fabricated with equal ease. Although a batch process is not suitable for mass scale industrial production, PLD is a versatile technique, efficient and convenient for high quality basic research.  This thesis illustrates the use of PLD technique to study the emerging trends in tailoring multifunctional magnetic thin films both from basic nanoscience and device development point of view.

         After a comprehensive review of magnetism in chapter 1: entitled ‘A journey through classical to modern trends in magnetism, and multifunctional thin film devices’ followed by a reasonably thorough discussion on Pulsed Laser thin film technique in Chapter 2, we present:

    1. Studies of tailoring composite high energy product permanent magnetic FePtB based thin films for applications in NEMS /MEMS, (Chapter 3).
    2. Study of search for new multiferroic materials by investigating the properties of Chromites. Crystalline Chromites are antiferromagnetic below 150oC.  However depositing thin films by PLD of the crystalline 95.5% dense targets produced by Surface Plasma Sintering, we discovered that the resulting films were amorphous and ferromagnetic beyond room temperature. Moreover advanced spectroscopic techniques revealed that the amorphized state is metallic with Cr in a mixed valence state.   An understanding of the underlying physics of the observed phenomenon has been carried out based on first principles calculations.  These results are now being considered for publication in a high profile journal.  Extensive studies on the films showing that these materials are ferromagnetic, but not ferroelectric are discussed in chapter 4. A preliminary presentation of these studies was pier reviewed and published in MRS symposium proceedings.
    3. Fabrication of Room temperature, Transparent, high moment soft ferromagnetic amorphous Bulk metallic glass based FeBNbY thin films by PLD, suitable for Nanolithography in NEMS/MEMS device development .  (Chapter 5)

    From a basic study point of view on new trends on magnetism we present:

    4. The use of PLD technique to demonstrate room temperature ferromagnetism in undoped MgO, and V-doped MgO thin films.  Both of these oxides which do not contain any intrinsically magnetic elements and are diamagnetic in their bulk form belong to a new class of magnetic films, the so called d0magnets signifying that robust above room temperature ferromagnetism arising from defects and controlled carriers and no occupied d-states can be tailored in semiconductors and insulators.  These, mostly ZnO and MgO based thin films which may be classified as Dilute Magnetic Semiconductors, DMS, and Dilute Magnetic Insulators, DMI, are now the materials of active interest in future Electronics involving components which exploit both charge and spin of electrons in the arena of SPINTRONICS.

    Extensive characterization of magnetic, electrical, optical properties and microscopic structure has ensured development of high quality magnetic materials for future applications. Further research on these promising materials is expected to yield new generation spintronic devices for better performance in terms of efficiency, energy consumption and miniaturization of sizes.

  • 12.
    Nagar, Sandeep
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jayakumar, Onattu D.
    Bhabha Atomic Research Centre, Mumbai, India.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Room Temperature Ferromagnetic V-Doped MgO Nanoparticles2012In: Materials Express, ISSN 2158-5849, Vol. 2, no 3, p. 233-237Article in journal (Refereed)
    Abstract [en]

    MgO is a widely used material in ceramic and electronic industry. It is a well known insulator which has been used as a spacer layer in electronic circuits and magnetic tunnel junctions. We report room temperature ferromagnetism in undoped, and V doped MgO nanoparticles of the same size (similar to 39 nm diameter) produced by a two-step chemical process, but containing nominal 0.5, 0.7, 0.9, 1, 1.1, and 1.5 at.% V. Strikingly, the saturation magnetization shows an anomalous abrupt increase in its value to 80.2 memu/g for the 1 at% V doped nanoparticles. Also, high resolution TEM studies show that on doping with V the lattice parameters, d(111) in particular, increases from 2.42 angstrom [MgO] to 2.47 angstrom in the case of [MgO:V(1%)]. These results are consistent with recent theoretical predictions on a first principles basis which suggests that the observed ferromagnetism is sensitively dependent on the distance between the V-Mg-V-Mg. Vacancies.

  • 13.
    Nagar, Sandeep
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Masood, Ansar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Landsåker, P. C.
    Volotinen, T. T.
    Nikalsson, G. A.
    Granqvist, C. G.
    Magnetic and electronic properties of glassy (Fe72B24Nb4)95.5Y4.5 ferromagneticthin films fabricated using Pulsed Laser Deposition techniqueArticle in journal (Other academic)
    Abstract [en]

    Magnetic and electrical properties have been studied for (Fe72B24Nb4)95.5Y4.5 ferromagnetic thin films fabricated using Pulsed Laser Deposition technique. Magnetic characterization shows that these thin films are soft ferromagnetic at room temperature with high saturating magnetic moment (averaged at 372.5 emu/cc). Magnetic data indicates mixed orientation of magnetic moments where mostly in-plane orientation of magnetic moments along with a minority contribution from out of plane magnetic moments. This arrangement of mixed orientation of magnetic moment is attributed to energy of LASER beam used for deposition. Electrical characterization show peculiar thickness dependence of electrical transport and corresponding optical behavior. Temperature dependence of resistivity shows a negative temperature coefficient of resistance which is characteristic of amorphous state. Mott and Efros-Shklovskii hopping mechanism were found to work under different temperature and thickness regimes for these thin films. Since these thin films are amorphous hence their physical properties are independent of choice of substrate and hence present a major advantage while fabricating magneto-optic devices for NEMS.

  • 14.
    Nagar, Sandeep
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Masood, Ansar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Landsåker, P. C.
    Volotinen, T. T.
    Nikalsson, G. A.
    Granqvist, C. G.
    Innoue, Mitsuteru
    Takagi, Hiroyuki
    A new material for Magneto-Optical applications: (Fe72B24Nb4)95.5Y4.5 glassy thin filmArticle in journal (Other academic)
    Abstract [en]

    Magneto-Optical properties have been investigated for new kind of glassy thin films. 5, 8, 25 and 30 nm (Fe72B24Nb4)95.5Y4.5 thin films were fabricated using Pulsed LASER deposition (PLD) technique. These thin films were then compared to Fe thin films of same thickness deposited under similar conditions. Using inversion of spectroscopic transmittance and reflectance spectra in the wavelength range 300-2500nm, optical constant ε2(imaginary part of dielectric constant) was found. The optical properties resemble those of other transition metals and their alloys, being mainly determined by interband transitions in the studied wavelength range. The free electron contribution is not significant in this region, which is in line with their low electrical conductivity. These thin films also show large moment (~372.5emu/cc) and soft magnetic properties (coercivity of ~15 Gauss). Being glassy in nature, they can be easily fabricated on any kind of substrate and can tolerate high temperatures (Glass transition temperature for bulk material is close to 700°C [1]) without changing physical properties. Epitaxial and defect free growth of thin films are critical parameters for thin film fabrication. These can be avoided using amorphous materials hence (Fe72B24Nb4)95.5Y4.5 thin films has potential for new functional thin film structures and composites for magneto-optic applications.

  • 15.
    Nagar, Sandeep
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Catalan, G.
    Hong, J.
    Scott, J. F.
    Tyagi, A. K.
    Jayakumar, O. D.
    Shukla, R.
    Liu, Yi-Sheng
    Guo, Jinghua
    Room Temperature Ferromagnetism and Lack of Ferroelectricity in Thin Films of 'Biferroic?' YbCrO32009In: Novel Materials and Devices for Spintronics / [ed] Sanvito S, Heinonen O, Dediu VA, Rizzo N, Materials Research Society, 2009, Vol. 1183, p. 163-168Conference paper (Refereed)
    Abstract [en]

    Search for novel multi-functional materials, especially multiferroics, which are ferromagnetic above room temperature and at the same time exhibit a ferroelectric behavior much above room temperature, is an active topic of extensive studies today Ability to address an entity with an external field, laser beam, and also electric potential is a welcome challenge to develop multifunctional devices enabled by nanoscience While most of the studies to date have been on various forms of Bi and Ba based Ferrites, rare earth chromites are a new class of materials which appear to show some promise However m the powder and bulk form these materials are at best canted antiferromagnets with the magnetic transition temperatures much below room temperature In this presentation we show that thin films of YbCrO3 deposited by Pulsed Laser Deposition exhibit robust ferromagnetic properties above room temperature It is indeed a welcome surprise and a challenge to understand the evolution of above room temperature ferromagnetism in such a thin film The thin films are amorphous in contrast to the powder and bulk forms which are crystalline The magnetic properties are those of a soft magnet with low coercivity We present extensive investigations of the magnetic and ferroelectric properties, and spectroscopic studies using XAS techniques to understand the electronic states of the constituent atoms in this novel Chromite While the amorphous films are ferromagnetic much above room temperature, we show that any observation of ferroelectric property in these films is an artifact of a leaky highly resistive material

  • 16. Singhal, Sonal
    et al.
    Chawla, Amit Kumar
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Gupta, Hari Om
    Chandra, Ramesh
    Photoluminescence measurements in the phase transition region of Zn1-x Cd (x) S films2010In: Journal of nanoparticle research, ISSN 1388-0764, E-ISSN 1572-896X, Vol. 12, no 4, p. 1415-1421Article in journal (Refereed)
    Abstract [en]

    Thin films of Zn1-x Cd (x) S (0.1 a parts per thousand currency sign x a parts per thousand currency sign 0.5) were prepared by using pulsed laser ablation technique on corning glass substrates. Phase transition from cubic to hexagonal in Zn1-x Cd (x) S films is determined by X-ray diffraction analysis. We observed a lowering in the phase transition temperature with increase in the cadmium concentration. Transmission electron microscopy suggests the crystalline nature of thin films with average particle size of 15 nm. The grown Zn1-x Cd (x) S samples show the high peak intensity ratio of the near band edge emission to the defect center luminescence even at room temperature, which indicates the small concentration of complex defects in the samples. Photoluminescence measurement show stoichiometric dependence of the energy band gap and is found to have quadratic dependence on x.

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