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Transformation to Room Temperature Ferromagnetism on Amorphizing Chromite Thin Films
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
(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.

URN: urn:nbn:se:kth:diva-94882OAI: diva2:526314
under review,-only abstract page included. QS 2012Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-11Bibliographically approved
In thesis
1. Multifunctional magnetic materials prepared by Pulsed Laser Deposition
Open this publication in new window or tab >>Multifunctional magnetic materials prepared by Pulsed Laser Deposition
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.
Magnetic materials, thin films, pulsed laser depsoition, spintronics, chromites, MgO, NEMS, MEMS
National Category
Other Materials Engineering
urn:nbn:se:kth:diva-94852 (URN)978-91-7501-386-2 (ISBN)
Public defence
2012-05-29, F3, Lindstedtsvagen 26 KTH, Stockholm, 14:30 (English)
QC 20120511Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-11Bibliographically approved

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