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Multifunctional magnetic materials prepared by Pulsed Laser Deposition
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
2012 (English)Doctoral 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.

Place, publisher, year, edition, pages
Stokholm: KTH Royal Institute of Technology, 2012. , xxii, 140 p.
Keyword [en]
Magnetic materials, thin films, pulsed laser depsoition, spintronics, chromites, MgO, NEMS, MEMS
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-94852ISBN: 978-91-7501-386-2 (print)OAI: oai:DiVA.org:kth-94852DiVA: diva2:526228
Public defence
2012-05-29, F3, Lindstedtsvagen 26 KTH, Stockholm, 14:30 (English)
Opponent
Supervisors
Note
QC 20120511Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-11Bibliographically approved
List of papers
1. Exchange-coupled FePtB nano-composite hard magnets produced by pulsed laser deposition
Open this publication in new window or tab >>Exchange-coupled FePtB nano-composite hard magnets produced by pulsed laser deposition
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2010 (English)In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 171, no 1-3, 62-68 p.Article in journal (Refereed) Published
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.

Keyword
FePtB thin films, Hard magnetic material, Exchange-coupled magnets, Nano-composite magnet, Pulsed laser deposition, Thin films
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-29506 (URN)10.1016/j.mseb.2010.03.070 (DOI)000279680600013 ()2-s2.0-77953158167 (Scopus ID)
Note
QC 20110203Available from: 2011-02-03 Created: 2011-02-02 Last updated: 2017-12-11Bibliographically approved
2. Room Temperature Ferromagnetism and Lack of Ferroelectricity in Thin Films of 'Biferroic?' YbCrO3
Open this publication in new window or tab >>Room Temperature Ferromagnetism and Lack of Ferroelectricity in Thin Films of 'Biferroic?' YbCrO3
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2009 (English)In: Novel Materials and Devices for Spintronics / [ed] Sanvito S, Heinonen O, Dediu VA, Rizzo N, Materials Research Society, 2009, Vol. 1183, 163-168 p.Conference paper, Published 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

Place, publisher, year, edition, pages
Materials Research Society, 2009
Series
Materials Research Society Symposium Proceedings, ISSN 0272-9172 ; 1183
Keyword
rare-earth orthochromites, chromites
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-27955 (URN)000284863300024 ()2-s2.0-77951013321 (Scopus ID)978-160511156-8 (ISBN)
Conference
2009 MRS Spring Meeting; San Francisco, CA; United States; 14 April 2009 through 17 April 2009
Note

QC 20110104

Available from: 2011-01-04 Created: 2011-01-03 Last updated: 2014-10-24Bibliographically approved
3. Transformation to Room Temperature Ferromagnetism on Amorphizing Chromite Thin Films
Open this publication in new window or tab >>Transformation to Room Temperature Ferromagnetism on Amorphizing Chromite Thin Films
(English)Article in journal (Other academic) Submitted
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.

Identifiers
urn:nbn:se:kth:diva-94882 (URN)
Note
under review,-only abstract page included. QS 2012Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-11Bibliographically approved
4. Magnetic and electronic properties of glassy (Fe72B24Nb4)95.5Y4.5 ferromagneticthin films fabricated using Pulsed Laser Deposition technique
Open this publication in new window or tab >>Magnetic and electronic properties of glassy (Fe72B24Nb4)95.5Y4.5 ferromagneticthin films fabricated using Pulsed Laser Deposition technique
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(English)Article in journal (Other academic) Accepted
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.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-94859 (URN)
Note
QS 2012Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-11Bibliographically approved
5. A new material for Magneto-Optical applications: (Fe72B24Nb4)95.5Y4.5 glassy thin film
Open this publication in new window or tab >>A new material for Magneto-Optical applications: (Fe72B24Nb4)95.5Y4.5 glassy thin film
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(English)Article in journal (Other academic) Accepted
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.

National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-94863 (URN)
Note
QS 2012Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-11Bibliographically approved
6. Room temperature ferromagnetism in pristine MgO thin films
Open this publication in new window or tab >>Room temperature ferromagnetism in pristine MgO thin films
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2010 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23Article in journal (Refereed) Published
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.

Keyword
ENERGY
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-13939 (URN)10.1063/1.3447376 (DOI)000278695900048 ()2-s2.0-77953525394 (Scopus ID)
Note

QC20100705

Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2017-12-12Bibliographically approved
7. Room Temperature Ferromagnetic V-Doped MgO Nanoparticles
Open this publication in new window or tab >>Room Temperature Ferromagnetic V-Doped MgO Nanoparticles
2012 (English)In: Materials Express, ISSN 2158-5849, Vol. 2, no 3, 233-237 p.Article in journal (Refereed) Published
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.

Keyword
Oxides, MgO, Doping, Magnetic Nanoparticles, d(0) Magnetism
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-94885 (URN)10.1166/mex.2012.1076 (DOI)000311914200005 ()2-s2.0-84871549918 (Scopus ID)
Funder
VinnovaSwedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20130108. Updated from accepted to published.

Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2013-01-08Bibliographically approved

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