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Ferromagnetic resonance in films with growth induced anisotropy
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis discusses two different magnetic materials: epitaxial yttrium iron garnet (YIG) and heteromorphous CoFeB-SiO2 films.

YIG films were grown by pulse laser deposition (PLD) techniques onto gadolinium gallium garnet (GGG) substrates of (111) and (001) crystal orientations. Using stoichiometric and overstoichiometric ablative targets, we developed two types of YIG submicron films. The films grown from overstoichiometric targets have magnetic properties slightly different from standard liquid phase epitaxy (LPE) YIGs. They also demonstrate good substrate matching and approximately 6% nonstoichiometry. In contrary, films grown from stoichiometric targets posses surprisingly high values of uniaxial anisotropy, meanwhile cubic anisotropy is reduced several times. These films also reveal strong lattice distortions and nonstoichiometry around 17%.

Employing Weiss molecular field theory and single-ion anisotropy model we determined the preferential occupancy of the octahedral [a] positions in the YIG cubic lattices by Fe3+ vacancies. The vacancies were found to be preferentially oriented along the growth direction perpendicular to the film surface. We called this effect “deformation blockade”.

Different magnetostatic surface wave (MSSW) filters were also demonstrated. The filters employ high uniaxial anisotropy in YIG submicron films with magnetic losses ΔH ~ 1 Oe.

 Heteromorphous CoFeB-SiO2 films were deposited onto glass substrates employing carrousel magnetron sputtering. This novel technique allows amorphous films fabrication with record high in-plane anisotropy. The induced anisotropy fields here are approximately dozen times greater the values achieved using conventional growth technique when external bias field is applied during deposition process.

Interesting observations were made studying CoFeB-SiO2 magnetization dynamics in the wide frequency range from 500 kHz up to 15 GHz.  Two different anomalies of the magnetic susceptibility were found at the field of in-plane anisotropy Hp and critical field Hcr (0 < Hcr < Hp). We explained the anomalies appearance by sequence of the domain walls transformations so that Néel-Bloch-Néel domain wall transition stands for the instability at H = ±Hcr and transition from the uniformly magnetized state to the domain state with Néel domain wall and vice versa is responsible for the instability at H = ±Hp.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , xv, 114 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2011:16
Keyword [en]
ferromagnetic resonance, magnetic anisotropy, single-ion anisotropy model, ferrites, magnetic epitaxial films, magnetostatic waves, pulsed laser deposition, magnetic alloys, domains, domain wall transformations
National Category
Condensed Matter Physics Other Electrical Engineering, Electronic Engineering, Information Engineering Other Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-48248ISBN: 978-91-7501-193-6OAI: oai:DiVA.org:kth-48248DiVA: diva2:457103
Public defence
2011-12-14, Ka-C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Note
QC 20111122Available from: 2011-11-22 Created: 2011-11-16 Last updated: 2011-11-22Bibliographically approved
List of papers
1. Pulsed Laser Deposited Y3Fe5O12 Films for Magnetostatic Wave Band Pass Filters
Open this publication in new window or tab >>Pulsed Laser Deposited Y3Fe5O12 Films for Magnetostatic Wave Band Pass Filters
2009 (English)In: Solid State Phenomena, ISSN 1012-0394, Vol. 152-153, 377-380 p.Article in journal (Refereed) Published
Abstract [en]

Y3Fe5O12 (YIG) films were pulsed laser deposited onto the Gd3Ga5O12(111) substrates. Processing conditions were optimized to obtain films with a narrow ferromagnetic resonance (FMR) linewidth: 0.9 Oe in 1.22 mu m thick YIG at 9 GHz. Due to sharp film-to-substrate interface YIG films remain strained hence possess unusually high lattice mismatch induced uniaxial anisotropy H-u = - 880 Oe. We fabricated and tested magnetostatic surface wave (MSSW) band pass hybrid-type filters with YIG film lain on transducers alumina board. MSSW filter with antennas areal size of 2 mm(2) at 7.5 GHz shows insertion loss - 9 dB and a resonant 3 dB bandwidth as narrow as 12.5 MHz.

Keyword
yttrium iron garnet, epitaxial film, ferromagnetic resonance, uniaxial anisotropy, magnetostatic surface wave, S parameter, insertion loss, resonant bandwidth
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-30416 (URN)10.4028/www.scientific.net/SSP.152-153.377 (DOI)000270899200091 ()2-s2.0-76149092486 (ScopusID)
Note
QC 20110228 4th Moscow International Symposium on Magnetism, Moscow State Univ, Moscow, RUSSIA, JUN 20-25, 2008Available from: 2011-02-28 Created: 2011-02-24 Last updated: 2011-11-22Bibliographically approved
2. Submicron Y3Fe5O12 Film Magnetostatic Wave Band Pass Filters
Open this publication in new window or tab >>Submicron Y3Fe5O12 Film Magnetostatic Wave Band Pass Filters
2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 105, no 3Article in journal (Refereed) Published
Abstract [en]

Thin Y3Fe5O12 (YIG) films were pulsed laser deposited onto Gd3Ga5O12 (111) and (001) substrates. Processing conditions were optimized to obtain compressively strained films with a ferromagnetic resonance linewidth at 9 GHz as narrow as 0.9 Oe and high uniaxial magnetic anisotropy H-u=-880 Oe. Several designs of magnetostatic surface wave (MSSW) bandpass filters were fabricated and tested: 0.45 and 0.22 mu m thick YIG films lain on transducers alumina board and with microstripe transducers defined directly onto YIG film, with effective antenna areal sizes of 2 and 0.4 mm(2). The MSSW filter with 2 mm(2) antenna shows, at 7.5 GHz, insertion loss -9 dB and a resonant -3 dB bandwidth as narrow as 12.5 MHz.

Keyword
band-pass filters, ferromagnetic resonance, magnetic anisotropy, magnetic thin films, magnetostatic surface waves, magnetostatic wave, devices, pulsed laser deposition, yttrium compounds, yttrium-iron-garnet, pulsed-laser deposition, ferromagnetic-resonance, yig-films
Identifiers
urn:nbn:se:kth:diva-18178 (URN)10.1063/1.3075816 (DOI)000263409700072 ()2-s2.0-60449106985 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-11-22Bibliographically approved
3. Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy I
Open this publication in new window or tab >>Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy I
2009 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 106, no 12Article in journal (Refereed) Published
Abstract [en]

Recently we sintered by pulsed laser deposition (PLD) technique the epitaxial Fe-deficient yttrium iron garnet (YIG) films with ferromagnetic resonance (FMR) linewidth as narrow as 0.9 Oe, the uniaxial anisotropy as high as H-u=-880 Oe, and demonstrated them feasible for magnetostatic waves band pass filter application [Manuilov , J. Appl. Phys. 105, 033917 (2009)]. Here we explore the origin of unusually high noncubic magnetic anisotropy. Using the angular resolved FMR spectroscopy we found that in addition to strong uniaxial anisotropy, cubic magnetic anisotropy experienced almost fivefold reduction compared to standard YIG grown by liquid phase epitaxy. Molecular field theory was employed to calculate saturation magnetization 4 pi M-s, cubic magnetocrystalline K-1, and uniaxial anisotropy K-u in garnets with Fe vacancies. The modeling utilizes crystal field parameters that we revealed from earlier published experimental data on diamagnetic ion substituted Y3Fe5O12 and Fe-substituted isomorphous diamagnetic garnets. Consistent single ion anisotropy crystal field theory perfectly fits experimentally observed high saturation magnetization, reduction in cubic, and appearance of strong uniaxial anisotropy in PLD-grown Fe-deficient YIG films. The redistribution of Fe vacancies between different magnetic sublattices was quantified and confirmed that in YIG(111) films ferric ions preferentially leave vacant octahedrally coordinated sites. Simulation of growth induced anisotropy proves the ordering of Fe3+ vacancies within octahedral sites. At equal number of available ferric ions and vacancies, the latter populate the octahedrons with distortion axis perpendicular to the film surface with the probability equal to 0.67. Deformation blockage of octahedral complexes with distortion axes directed along the film surface reduces this probability down to 0.14.

Keyword
crystal field interactions, diamagnetic materials, ferrites, ferromagnetic resonance, garnets, magnetic anisotropy, magnetic, epitaxial layers, pulsed laser deposition, vacancies (crystal), yttrium, compounds, yttrium-iron-garnet, growth-induced anisotropy, ferromagnetic-resonance, paramagnetic-resonance, yig-films
Identifiers
urn:nbn:se:kth:diva-19087 (URN)10.1063/1.3272731 (DOI)000273216500064 ()2-s2.0-73849083000 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-11-22Bibliographically approved
4. Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy II
Open this publication in new window or tab >>Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy II
2010 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 108, no 1, 013902- p.Article in journal (Refereed) Published
Abstract [en]

Recently we found epitaxial Fe-deficient yttrium iron garnet Y3Fe5-tO12-3t/2 (YIG) films pulsed laser deposited onto the (111) and (001) face of Gd3Ga5O12 single crystal experience, respectively, strong rhombohedral and tetragonal distortions and possess unusual magnetic anisotropy. Using the crystal field theory, we explained these anomalies and showed in YIG (111) films ferric ion vacancies preferentially occupy octahedral complexes, order themselves along the [111] growth direction, cause rhombohedral lattice distortions, generate strong uniaxial and significantly reduce cubic crystalline anisotropy, Manuilov et al., [J. Appl. Phys. 106, 123917 (2009)]. Oxygen vacancies govern electrical neutrality and in spite of high concentration (in access of 7 at. %) they are perfectly ordered that is indicated by narrow ferromagnetic resonance linewidth. The present paper aims to compare growth anisotropies induced in (111) and (001) epitaxial Fe-deficient YIG films. Ordering of vacancies appeared to be different in (111) and (001) oriented YIG films. In highly Fe-deficient YIG (001) we found much smaller imbalance in redistribution of vacancies between the octa-and tetrahedral magnetic sublattices. This feature together with a weaker crystal field in tetrahedral Fe3+-O2- complexes result in reduced growth induced magnetic anisotropy in (001) oriented tetragonal distorted YIGs compared to rhombohedral distorted YIG (111) films.

Keyword
IRON-GARNET FILMS, GROWTH-INDUCED ANISOTROPY, FERROMAGNETIC-RESONANCE, YIG-FILMS
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:kth:diva-29462 (URN)10.1063/1.3446840 (DOI)000280000400054 ()2-s2.0-77955210310 (ScopusID)
Funder
Swedish Research Council
Note
QC 20110208Available from: 2011-02-08 Created: 2011-02-02 Last updated: 2011-11-22Bibliographically approved
5. Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy
Open this publication in new window or tab >>Ferromagnetic resonance, magnetic susceptibility, and transformation of domain structure in CoFeB film with growth induced anisotropy
2011 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 8, 083926- p.Article in journal (Refereed) Published
Abstract [en]

Field dependence of magnetic susceptibility in nanocrystalline CoFeB film was studied in a wide frequency range from 500 kHz to 15 GHz. Anomalies of the susceptibility were detected exciting CoFeB film with a solenoidal coil, microwave strip line, in the tunable microwave cavity as well as employing magneto-optical domains imaging. Critical spin fluctuations in the form of "soft" modes were observed in a whole range of orientations of magnetic field perpendicular to the "easy" magnetic axis. A sequence of domain structure transformations was extensively examined in a "hard" direction in in-plane magnetic field reduced below the field of uniaxial anisotropy H-p = 535Oe. At first, uniformly magnetized state in CoFeB film transforms to stripe domains separated by low angle Neel domain walls (DWs) parallel to the "hard"-axis. Then, at critical field H-cr = 232 Oe, Neel DWs gradually convert to the"easy"-axis oriented Bloch DWs loaded with vertical Bloch lines (VBLs). After field reversal at H = H-cr, backward conversion of VBL-loaded Bloch DWs to Neel DWs results in instantaneous energy release and sharp anomaly of magnetic susceptibility. Appearance of critical spin fluctuations accomplishes domains transformation to the uniformly magnetized state at H = 535 Oe. 

Keyword
BLOCH, WALLS
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-33972 (URN)10.1063/1.3559732 (DOI)000290047000118 ()2-s2.0-79955710753 (ScopusID)
Note
QC 20110530Available from: 2011-05-30 Created: 2011-05-23 Last updated: 2011-11-22Bibliographically approved
6. Improving of MSSW filter based on PLD-grown YIG
Open this publication in new window or tab >>Improving of MSSW filter based on PLD-grown YIG
(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-48603 (URN)
Note
QS 2011Available from: 2011-11-22 Created: 2011-11-22 Last updated: 2011-11-22Bibliographically approved

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