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Pulsed laser deposited Y3Fe5O12 films: Nature of magnetic anisotropy I
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.ORCID iD: 0000-0001-8774-9302
KTH, School of Information and Communication Technology (ICT), Material Physics.
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.

Place, publisher, year, edition, pages
2009. Vol. 106, no 12
Keyword [en]
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
URN: urn:nbn:se:kth:diva-19087DOI: 10.1063/1.3272731ISI: 000273216500064ScopusID: 2-s2.0-73849083000OAI: diva2:337134
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-11-22Bibliographically approved
In thesis
1. Ferromagnetic resonance in films with growth induced anisotropy
Open this publication in new window or tab >>Ferromagnetic resonance in films with growth induced anisotropy
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.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2011:16
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
urn:nbn:se:kth:diva-48248 (URN)978-91-7501-193-6 (ISBN)
Public defence
2011-12-14, Ka-C2, KTH-Electrum, Isafjordsgatan 26, Kista, 10:15 (English)
Swedish Research Council
QC 20111122Available from: 2011-11-22 Created: 2011-11-16 Last updated: 2011-11-22Bibliographically approved

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