magnetized epitaxial films and bulk monocrystals of barium hexaferrite ... Hexagonal ferrites as the device base of super high frequency electronics are actual of ...
MSMW'07 Symposium Proceedings. Kharkov, Ukraine, June 25-30, 2007
STATIC AND DYNAMIC HYSTERESIS LOOPS IN SAMPLES OF UNIAXIAL BARIUM HEXAFERRITE T.G. Chamor, V.I. Kostenko, A.F. Lozenko, A.M Sorochak, L.V. Chevnyuk
The Kyiv National Taras Shevchenko university, radiophysics faculty Adress: Bildg. 2, Acad Glushkov Ave. 2, Kyiv, 03022, Ukraine Tel. +380445266403, E-mail ctamnila@univ. kiev. ua, kvi@univ. kiev. ua Frequency-field dependences of absorber spectrums and static hysteresis curves in normally magnetized epitaxial films and bulk monocrystals of barium hexaferrite (BaFeI2019) are investigated by tests. Experimental data in the transition range from multidomain state before saturation and vice versa are compared.
Hexagonal ferrites as the device base of super high frequency electronics are actual of the millimeter wavelength mode [1]. Using of epitaxial films instead of bulk monocrystals allows creating devices in integralplanar performance. Many research works are devoted to the investigation of magnetic and super high frequency parameters [1,2] from urgency subjects. In the work [3] the hysteresis effect of frequency-field dependence in BaFeI2019 was investigated. Hysteresis effect in double layer of polycrystalline ferromagnetic/antiferromagnetic (F/AF) is analyzed in work [4]. High-frequency and hysteresis properties of double-sided barium hexaferrite films grown on magnesium oxide MgO (I 1) substrates were investigated in work [5]. The authors of this work first obtained the hysteresis of frequency-field dependence ferromagnetic resonance (FMR) however they didn't compare static and dynamic hysteresis loops of the same samples. In addition the deposited layer of ferrite BaFe12019 was rather a piece-wise crystalline sample than monocrystal one. In our previous work [3] the hysteresis of frequency-field dependence FMR in epitaxial films of BaFeI2019 grown on substrates of hexagallate strontium (HGS) by the liquid phase epitaxy was investigated. However, static hysteresis loops were not measured. In this work both static and dynamic characteristics of hysteresis phenomena in the epitaxial films and bulk monocrystals barium hexaferrite are experimentally investigated in the process of magnetic reversal. Main attention is concentrated on studying of direct and inverse branches of hysteresis effect in ranges of transition from saturated to unsaturated condition both for frequencyfield and static hysteresis loops. During tests the external fields was directed in parallel to the easy direction. Tests demonstrated that a dispersion relation of the frequency-field dependence splits asunder into two branches, which corresponds to direct and inverse loops of static hysteresis effect. Theoretical calculations were conducted according to the formula [6] for the direct branch of frequency-field dependence FMR in the domain region W1:
co2
A+B2 A2 +BD+AC-[(A2+Bi2+BD+AC) -4(A2 -B2)(AC-BD)]j2
(1)
where A, B, C, D coefficients, dependent on the external field Ho and on the ferrite layer thickness t. Ha- is the field of crystallographic anisotropy, which is equal to 16.5 kOe for the epitaxial film and for the monocrystal plates 17.4 kOe, 4nM is the saturation magnetization and equals 4.71 kG. For the saturated region, the calculation of the frequency spectrum is conducted according to the fonnula [6]: -
oo(HO) (01
=
Y(Ha -4rM+Ho)
(2)
In represented Figures calculated curves are shown by solid lines and experiment ones by points. Direct and inverse directions of the external magnetic field are marked out by arrows. The frequency-field dependence of epitaxial film barium hexaferrite (No. 2-8) is shown in Figure 1, the thickness of epitaxial film is t=8 pm, the thickness substrate is d=450 pm. Previously the stripe domain structure (SDS) was formed in the film. The calculated curve co, coincides with tested one only qualitatively. Possibly it is connected with the fact that the real thickness of the ferrite layer didn't agree with one determined by the producer. In addition quality of the film was different from perfect monocrystal film wasn't simply connected magnetic structure and it was non-homogeneous by thickness. -
1-4244-1237-4/07/$25.00 ©2007 IEEE
MSMW'07 Symposium Proceedings. Kharkov, Ukraine, June 25-30, 2007 50-
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Fig.2. Static hysteresis loop behavior of sample No.2-8
For comparison, the static hystetesis loop for the same film is shown in Figure 2. As one can see, there is the perfect correspondence between static and dynamic hysteresis loops in the region of transition sample from saturated state to domain one. Measurements of frequency-field dependencies FMR were conducted also for more perfected epitaxial film of the same thickness presented by another producer. In the Figure 3 the frequencyfield dependence for the 7 pm thick epitaxial film (No. 24-1) and with thickness of HGS substrate d=790 ptm. As we can see, there is a better coincidence between theoretical and experimental curves. In contrast to the sample No. 2-8, transition from saturated region to one domain is spasmodic instead of smooth transition. The spasmodic transition was observed in more perfect samples of bulk monocrystals of hexaferrite. Theoretical curves for these samples are well corresponded with experimental results. In the region of saturation up to four magnetostatic modes can be observed. N
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In Figure 4 the frequency-field dependence is presented for a monocrystal plate of BaFeI2019, thickness t=62 ,tm and dimensions are axb=2.45x2.0 mm2 with SDS. To avoid encumbering, in Figure 5 the only one mode of magnetostatic oscillation W0)1 It should be noted that value Hbr is greater for the higher modes than for the main mode that demonstrates non-simultaneous transition into domain region for various modes. The static hysteresis loop for this monocrystal plate is shown in Figure 5. This plate is quasi free from defect because the coercive field is zero, i.e. Hk-0. It was well marked discontinuous jump at the field Hbr (the area selected by a .
792
MSMW'07 SSynposium Proceedings. Kharkov, Ukraine, June 25-30, 2007
circle, resulted on figure 6 in a megascopic scale) on the static hysteresis curve in the case of inverse movement H. Magnetic fields Hbr, Hsat, are measured on static and dynamic hysteretic loops demonstrate well coincidence. Since spasmodic transition from the saturated region to domain one at the field Hbr was caused by delay of generation and growth of magnetic reversal centers than the character and parameters of transition can serve as a criterion of the epitaxial films quality.
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