KR102560146B1 - Hexaferrites, composition of radio wave absorber comprising the same and radio wave absorber sheet - Google Patents

Abstract

The present invention relates to a hexagonal ferrite capable of effectively absorbing electromagnetic waves in a microwave millimeter wave frequency band of 50 GHz or higher by substituting two or more kinds of cations in M-type hexagonal ferrite, a radio wave absorber composition, and a radio wave absorbing sheet including the same.
Hexagonal ferrite according to an embodiment of the present invention is represented by Formula 1 below.
[Formula 1]
SrFe _12-2x M _1x M _2x O ₁₉
(Where M ₁ is Zn or Mn, M ₂ is Ti or Zr, and 0≤x≤2)
A radio wave absorber composition according to an embodiment of the present invention may include the aforementioned hexagonal ferrite and a polymer.
A radio wave absorbing sheet according to an embodiment of the present invention may include the aforementioned hexagonal ferrite and a polymer.

Description

Hexagonal ferrite, radio wave absorber composition, and radio wave absorbing sheet containing the same

The present invention relates to hexagonal ferrite, a radio wave absorber composition, and a radio wave absorbing sheet including the same. Specifically, the present invention relates to a hexagonal ferrite capable of effectively absorbing electromagnetic waves in a microwave millimeter wave frequency band of 50 GHz or higher by substituting two or more types of cations in M-type hexagonal ferrite, a radio wave absorber composition, and a radio wave absorbing sheet including the same.

As a method of blocking radio waves generated from an IC chip in a circuit of an existing electronic device, a method of surrounding a metal can such as a shield can is most commonly used. When an electromagnetic wave is incident on a metal in free space, it can block the electromagnetic wave by reflecting most of the electromagnetic wave on the surface due to the high electrical conductivity of the metal. However, reflected waves may cause electromagnetic interference (EMI) in other parts of the circuit, and radio waves may pass through to the PCB without a shield can, so it is not a complete radio wave shielding method.

In addition, metal plate-like magnetic powder sheets are being used as electron absorbers in various fields such as notebook PCs, smartphones, and display devices. As a Fe-Si-Al alloy composition, it is commercialized and widely used under the trade name called Sendust. Sendust sheet shields magnetic fields with high magnetic permeability and also has characteristics of absorbing electromagnetic waves in the form of a dispersed form of sheet metal magnetic powder in a polymer binder rather than a continuous metal film. However, the commercially available Sendust shielding sheet shows good absorption performance in the range of hundreds of GHz or less, but its electron absorption characteristics are very poor in the range of X-band (8 ~ 12 GHz) and above. This is due to the reflection characteristics of radio waves due to the excellent electrical conductivity of the metal powder, and the reflected electromagnetic waves can become another electromagnetic interference (EMI) factor in other circuits.

An object of the present invention is to provide a hexagonal ferrite with improved absorption characteristics of electromagnetic waves in a GHz frequency band including X-band (8 to 12 GHz) than conventional sendust sheets, a radio wave absorber composition including the same, and a radio wave absorbing sheet including the same.

Hexagonal ferrite according to an embodiment of the present invention is represented by Formula 1 below.

[Formula 1]

SrFe _12-2x M _1x M _2x O ₁₉

(Where M ₁ is Zn or Mn, M ₂ is Ti or Zr, and 0≤x≤2)

A radio wave absorber composition according to an embodiment of the present invention may include the aforementioned hexagonal ferrite and a polymer.

A radio wave absorbing sheet according to an embodiment of the present invention may include the aforementioned hexagonal ferrite and a polymer.

The hexagonal ferrite of the present invention can effectively absorb electromagnetic waves in the microwave millimeter wave frequency band of more than X-band and less than 50 GHz by substituting two or more kinds of cations in M-type hexagonal ferrite. In addition, it can be used as an absorber of the X band band (8-12 GHz) and the Ku band band (12-18 GHz) by greatly lowering the crystal magnetic anisotropy with a smaller substitution amount than other existing substitution compositions.

The radio wave absorber composition and the radio wave absorber sheet of the present invention significantly improve electromagnetic wave absorption characteristics in a GHz frequency band including X-band (8 to 12 GHz) compared to conventional sendust sheets. In addition, it is highly useful as an electromagnetic wave absorber according to various frequency bands such as various frequency band areas (S, C, X band).

1 is an XRD pattern of hexagonal ferrite prepared according to Example 1.
2 (a) to (e) show the microstructure of the SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0, 0.5, 1.0, 1.5, 2.0) sample of Example 1. 2(f) to (h) are SEM-BSE (backscattered electron) images of x = 1.0, 1.5 and 2.0 samples.
3 is a MH curve for SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1) -epoxy composite samples.
Figure 4 shows the real and imaginary parts of the complex permittivity (ε' and ε") and permeability (μ' and μ") spectra (100 MHz ≤ f ≤ 18 GHz) of the SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1) powder-epoxy (10 wt%) composite sample. indicate
5 is a RL map as a function of sample thickness (d) and frequency (f) for SrFe _{12 - 2x} Zn _x Zr _x 0 ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.5, 2.0) powder-epoxy (10 wt %) composites.
Figure 6 is a RL versus f plot of SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0.7, 0.8, 0.9, 1.0, 1.1) powder-epoxy composites to determine the optimal absorber thickness (mm).

Hereinafter, various embodiments of this document will be described with reference to the accompanying drawings. Examples and terms used therein are not intended to limit the technology described in this document to specific embodiments, and should be understood to include various modifications, equivalents, and/or substitutes of the embodiments.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Hexagonal ferrite according to various embodiments of the present invention is represented by Chemical Formula 1 below.

[Formula 1]

SrFe _{12 - 2x} M _1x M _2x O ₁₉

(Where M ₁ is Zn or Mn, M ₂ is Ti or Zr, and 0≤x≤2)

That is, the hexagonal ferrite of the present invention is characterized in that M-type Sr-hexagonal ferrite is substituted with two or more kinds of cations. More specifically, M ₁ ²⁺ and M ₂ ⁴⁺ are simultaneously substituted with any one of Mn, Zn, Zr and Ti. The hexagonal ferrite of the present invention is characterized in that M-type Sr-hexagonal ferrite is substituted with any one from the group consisting of Mn-Ti, Zn-Ti and Zn-Zr.

Preferably ^, the hexagonal ferrite of the present ^invention may be simultaneously substituted with Zn ²⁺ and Zr ⁴⁺ cations. That is, the hexagonal ferrite of the present invention is characterized in that M-type Sr-hexagonal ferrite is substituted with Zn-Zr. At this time, hexagonal ferrite is SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (0 x 2) can be expressed as

The hexagonal ferrite of the present invention can be used as an absorber of the X band band (8-12 GHz) and the Ku band band (12-18 GHz) by significantly lowering the crystal magnetic anisotropy with a smaller substitution amount than other existing substitution compositions. Specifically, when 0.7≤x≤1.0, it can be applied as an absorber of the X band band (8-12 GHz) and the Ku band band (12-18 GHz). For example, when x = 0.9, high EM absorption can be exhibited in the X band (8-12 GHz) with the lowest return loss of less than -45 dB. In addition, when x = 0.8, it is possible to show a wide Ku band band (12-18 GHz) absorption performance satisfying RL <-19 dB at 11 ≤ f ≤ 18 GHz.

In addition, the ferromagnetic resonance of the hexagonal ferrite of the present invention is a main mechanism for absorbing electromagnetic waves, and the electromagnetic wave absorption characteristics can be changed by effectively adjusting the ferromagnetic resonance frequency.

These hexagonal ferrite powders can be obtained as powders by synthesizing each through a ceramic process through a solid-state reaction method or synthesizing by a chemical synthesis method such as a sol-gel method.

The radio wave absorber composition according to various embodiments of the present invention may include the aforementioned hexagonal ferrite.

As described above, preferably the hexagonal ferrite is SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (0≤x≤2) may have a composition.

The radio wave absorber composition according to various embodiments of the present invention may further include a polymer. Hexagonal ferrite can be dispersed within a polymer matrix. In this case, the polymer may include at least one selected from the group consisting of epoxy-based compounds, silane-based compounds, amino-based compounds, silicone-based compounds, polyolefin-based resins, and combinations thereof. Preferably, the polymer may be an epoxy. Alternatively, the polymer may include styrene-ethylene and butylene-styrene polymers.

In the radio wave absorber composition according to an embodiment of the present invention, the polymer may be included in an amount of 5 wt % to 20 wt % based on 100 wt % of the total weight of the composition. Preferably, the polymer may be included at 10 wt%.

The radio wave absorber composition of the present invention has improved radio wave absorber characteristics than conventional sendust sheets in absorbing characteristics of electromagnetic waves in a GHz frequency band including X-band (8 to 12 GHz).

In the radio wave absorber composition of the present invention, hexagonal ferrite is uniformly dispersed without precipitation or aggregation, and it can be easily manufactured into a radio wave absorber sheet or film using the same.

A radio wave absorber can be obtained by preparing such a radio wave absorber composition in the form of a film or sheet.

A radio wave absorbing sheet according to an embodiment of the present invention can be obtained from the radio wave absorber composition described above. A general liquid coating method such as comma coating or a variety of generalized manufacturing methods such as putting mixed dry powders in a mold and heating/pressing molding or injection may be applied to the fabrication of the sheet-type absorber.

In this case, the radio wave absorbing sheet may have a thickness of 0.1 mm to 3 mm. Through this optimized thickness, the ability to absorb radio waves can be remarkably improved.

The radio wave absorbing sheet of the present invention has significantly improved electromagnetic wave absorption characteristics in the GHz frequency band including X-band (8 to 12 GHz) compared to the conventional Sendust sheet.

The radio wave absorber composition and the radio wave absorber sheet of the present invention are highly useful as electromagnetic wave absorbers in various frequency bands such as various frequency bands (S, C, and X bands).

Hereinafter, it will be described in detail through specific embodiments of the present invention.

However, the following examples are only for exemplifying the present invention, and the present invention is not limited by the following examples.

Example 1 - Synthesis of hexagonal ferrite according to formula 1

SrFe _{12 - 2x} Zn _x Ti _x O ₁₉ , SrFe _{12 - 2x} Mn _x Ti _x O ₁₉ (x = 0, 0.5, 1.0, 1.5, 2.0), and SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.5, 2.0) were synthesized through a conventional solid-state reaction method. Precursor powders of SrCO ₃ , Fe ₂ O ₃ , MnCO ₃ , ZnO, ZrO ₂ (Kojundo Chemical, 99.9%) and TiO ₂ (Sigma-Aldrich, 99.9%) were weighed based on the cation ratio of the formula. The powder was mixed with water, dried and calcined in air at 1200 °C for 4 hours. The calcined samples were ball milled and calcined again at 1250 °C for 2 h in air to improve compositional homogeneity. The sample was then ground again into a fine powder.

Example 2 - Preparation of radio wave absorbing sheet

Hexagonal ferrite powder prepared in Example 1 and an epoxy binder (YD014, Kukdo Chemical) were mixed at 9: 1% by weight, put in a toroid type (inner diameter 3.04 mm, outer diameter 7.00 mm) metal molder, and pressed into a disc shape (diameter 15 mm) to produce a toroid shape. Finally, it was cured in air at 180 °C for 20 minutes. The volume fraction of epoxy in the final sample was ~50%.

Experimental Example 1-XRD pattern confirmation

Figure 1 shows the XRD pattern of M-type Sr-hexaferrites (SrM) (0≤x≤2.0) powder substituted with Zn-Ti, Mn-Ti and Zn-Zr, respectively, after the second calcination at 1250 ° C according to Example 1.

As shown in FIG. 1(a), SrM substituted with Zn-Ti (Zn-Ti:SrM) represents a single M-type hexagonal ferrite. It is shown that Zn-Ti completely dissolves in the SrM phase in the substitution range of x ≤ 2.0.

As shown in FIG. 1(b), in the case of Mn-Ti:SrM substituted with Mn-Ti, a single M-type phase can be identified for x ≤ 1.5, and a small number of secondary phase peaks, Fe ₂ TiO ₅ , can be observed.

As shown in (C) of FIG. 1 , Zn-Zr:SrM substituted with Zn-Zr shows large secondary phase peaks of ZnFe ₂ O ₄ , SrZrO ₃ and ZrO ₂ for x ≥ 1.5. In the case of x = 2.0, ZrFe ₂ O ₄ represents a primary peak. To reveal the solubility limits of Zn-Zr(x) in SrM, additional XRD analyzes were performed at 0.1 intervals for samples with x between 0.6 and 1.1. A clear secondary phase peak of the ZrFe ₂ O ₄ phase starts to appear at x = 1.0 and its intensity increases as x increases. In the inset of FIG. 1(c), the (220) peak of the sample appears around 2θ = 65 ^o . From x = 0 to x = 0.5, the peak shift to the left is large, and the peak position moves slightly to the left between x = 0.5 and x = 1.0, but it was confirmed that the peak position did not change beyond that. From this, it can be seen that secondary phases (ZnFe ₂ O ₄ , SrZrO ₃ , ZrO ₂ ) are formed as x increases for x > 1.0, and the solubility limit is approximately x=1.0.

Experimental Example 2-SrFe _12-2x Zn _x Zr _x O ₁₉ Observation of SEM images of

2 (a) to (e) show the microstructure of the SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0, 0.5, 1.0, 1.5, 2.0) samples of Example 1 calcined at 1250 °C. The average particle size (d _g ) decreased approximately as x increased. That is, d _g = 1.0, 1.0, 0.82, 0.80 and 0.65 μm for x = 0, 0.5, 1.0, 1.5 and 2.0, respectively. Samples with x ≤ 1.0 have only a single M-type phase. Secondary phases (ZnFe ₂ O ₄ , SrZrO ₃ , ZrO ₂ ) were formed and increased as x increased for x > 1.0, as shown in FIG. 1(c).

2(f) to (h) are SEM-BSE (backscattered electron) images of x = 1.0, 1.5 and 2.0 samples. Referring to (f) of FIG. 2, all grains in the x = 1.0 sample show almost the same contrast, but referring to (g) of FIG. 2, brighter grains begin to appear at x = 1.5, and (h), it can be seen that brighter spots increase at x = 2.0. Considering the previous XRD analysis result (Fig. 1(c)) and the average atomic weight of the secondary phase, Fig. The bright spots in 4(g) and 4(h) correspond to SrZrO ₃ .

Experimental Example 3 - saturation magnetization (4πM _S ) and coercivity (H _C ) check

3 is a MH curve for SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1) -epoxy composite samples. Sample compositions with smaller x intervals (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1) were also checked, since the solubility limit of SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ was found to be approximately x = 1.0.

The saturation magnetization (4πM _S ) and coercive force (H _C ) values of these samples are shown in Table 1 below. The 4πM-H curve in the low magnetic field range is shown in the inset of Fig. 3.

x 4πM _S
( kG ) H _C
( kOe ) ε'
( 1 GHz ) ε"
( 1 GHz ) μ _s '
( 3GHz ) f _FMR
(GHz) RL _{min .}
(dB) f _RLmin
(GHz) 0.5 1.875 0.624 7.37 1.08 1.00 > 18GHz - - 0.6 1.810 0.466 7.32 0.82 1.02 > 18GHz - - 0.7 1.681 0.270 7.08 0.45 1.05 15.1 -42.9 16.7 0.8 1.607 0.225 7.34 0.51 1.12 10.8 -38.6 11.8 0.9 1.409 0.158 7.16 0.21 1.19 8.33 -44.7 8.8 1.0 1.295 0.155 6.85 0.20 1.17 7.89 -49.7 8.6 1.1 1.191 0.152 7.02 0.13 1.17 7.26 -50.0 8.2

4πM _S for x = 0.5 sample is 1.875 kG and decreases as x increases. The reason is that the non-magnetic ions of Zn ²⁺ -Zr ⁴⁺ are replaced by magnetic Fe ³⁺ ions.

H _C decreases noticeably when increasing from x = 0.5 to x = 0.7, but decreases slightly from x = 0.7 to x = 0.9 and remains approximately constant above x = 0.9. The H _C value depends on the intrinsic and extrinsic properties of the magnetic material. Particle size is the dominant factor affecting H _C . It is well known that H _C decreases as the grain size of hexagonal ferrite increases. Considering that the average grain size of the x = 0.5 sample is larger than that of the x = 1.0 sample, the higher x is, the smaller the _HC is, and the strong intrinsic property change by Zn–Zr substitution overcomes the adverse external factors.

At x = 0.7, the ferromagnetic resonance ( f _FMR ) frequency is lowered to 15 GHz, and when the value of x increases to ~1.0, the ferromagnetic resonance frequency can be gradually lowered to around 7 GHz.

Here, it can be seen that above x = 1.0, Zn-Zr is not employed in the M-type hexagonal ferrite, and therefore the ferromagnetic resonance frequency is no longer effectively lowered and the electromagnetic wave absorption frequency band is no longer lowered.

Experimental Example 4 - Complex Permittivity and Permeability Spectrum

Figure 4 shows the real and imaginary parts of the complex permittivity (ε' and ε") and permeability (μ' and μ") spectra (100 MHz ≤ f ≤ 18 GHz) of the SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1) powder-epoxy (10 wt%) composite sample. indicate

In Table 1 above, the real (ε ') and imaginary (ε") parts of the permittivity at 1 GHz, the real part (μ _s ') and the maximum μ" value (f _FMR ) of the permeability in the normal region after the first transition (~3 GHz) are shown. In the ε' and ε" spectra shown in Fig. 4, as the frequency increases, ε' decreases for all samples, converging to ~7 and ε" approaches zero.

The real (μ') and imaginary (μ") parts of the permeability spectrum are shown in Figs. 4(c) and 4(d). The first transitions of μ' and μ" are related to domain wall motion (f < 2 GHz), peaks at higher frequencies (f > 2 GHz) and are caused by ferromagnetic resonance (FMR). A gradual μ" peak shift to the left was observed when increasing x from 0.7 to 0.9 in the μ" spectrum, and a very small peak shift was found between x = 0.9 and x = 1.0. Changes in the f _FMR are related to intrinsic property changes and may result from cation substitution. This is consistent with the change of H _C shown in FIG. 3 . The µ" peak positions and H _C values for samples with x = 0.9 to 1.1 appear very similar since the solubility limit of Zn-Zr in the M phase is approximately x = 1.0. The gradual increase in µs' as x increases up to 0.9 can be explained by Snoek's limit law given below.

where γ is a constant known as the gyromagnetic ratio and Ms is the saturation magnetization value. As the static real magnetic permeability (μs') decreases, f _FMR increases. This means that the change in high-frequency magnetic permeability characteristics is governed by the intrinsic magnetic parameter of crystalline magnetic anisotropy, which can be controlled by Zn-Zr substitution.

Experimental Example 5 - Measurement of electromagnetic wave absorption performance

According to transmission line theory, Reflection Loss (RL), which means electromagnetic wave absorption performance, can be measured using the Vector Network Analyzer: Keysight E5063A and Air-line (85050C) kit.

Using the above network analyzer, the complex permittivity and magnetic permeability were measured according to frequency, and the reflection loss (RL) representing the electromagnetic wave absorption characteristics was calculated from the values of the complex permittivity (εr = ε’ - jε″) and complex permeability (μr = μ’ - jμ″). Here, the calculation of RL can be calculated from the following two equations based on the transmission line theory.

where Z _in is the incident impedance of the absorber, Z ₀ is where εr = ε'- jε″ and μr = μ' - jμ″ are the complex permittivity and complex permeability, f is the frequency of the incident electromagnetic wave, c is the speed of light, and d is the thickness of the absorber. Here, the permittivity and magnetic permeability are functions independent of thickness, and the values of the real and imaginary parts (ε', ε″, μ', μ″) of the complex permittivity and permeability obtained according to the frequency and the d value in the range of 0 to 10 mm are continuously specified to obtain Z _in /Z ₀ , and RL spectra can be obtained by substituting it into the above formula.

As shown in Fig. 5(a) to (d), RL calculations are plotted on square f-d maps. The RL ≤ -10 dB region, which means EM absorption greater than 90%, is indicated by a solid black line. Within this region, regions with RL ≤ -20, -30 and -40 dB are also indicated by solid lines.

5 is a RL map as a function of sample thickness (d) and frequency (f) for SrFe _{12 - 2x} Zn _x Zr _x 0 ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.5, 2.0) powder-epoxy (10 wt %) composites.

In Fig. 5(a)-5(i), the strong EM absorption region at the bottom d, indicated by the rectangular box, starts to be observed at x = 0.7 and gradually shifts as x increases up to 1.0. The left edge of the absorption region is already present in the right part of the sample with x = 0.6 in Fig. 5(b). The EM absorption in the marked region is caused by a magnetic loss mechanism, i.e. FMR, which produces peaks in the μ″ spectra. Therefore, the gradual shift of the EM absorption area at x = 0.7, 0.8 and 0.9 is attributed to the μ″ peak shift shown in Fig. 4(d).

5(g) to (i), it can also be observed that the absorption intensity of the RL map for x decreases from x = 1.1 to 2.0. The decrease in μ″ peak height shown in Fig. 4(d) is due to weakening of the EM absorption. As mentioned earlier, the decrease in μ″ peak height for the x = 1.5 and 2.0 samples is due to the increase in the non-magnetic secondary phase.

Figure 6 is a RL versus f plot of SrFe _{12 - 2x} Zn _x Zr _x O ₁₉ (x = 0.7, 0.8, 0.9, 1.0, 1.1) powder-epoxy composites to determine the optimal absorber thickness (mm).

The values of RL _min and the frequency of RL _min (f _RLmin ) are shown in Table 1. Each sample represents RL _min < -30 dB, and f _RLmin shifts to lower frequencies as x increases. f _RLmin shifts to lower f as x increases from 0.7 to 0.9, but only slightly for x ≥ 0.9. Large changes up to x = 0.9 and then very small changes for x > 0.9 show the same trend for H _C , f _FMR and f _RLmin . All these changes are related to the amount of Zn-Zr substitution of the M-phase and the change in magnetic anisotropy. As indicated, f _{RL min} is similar to f _FMR for each sample and FMR is the dominant EM absorption mechanism in hexagonal ferrite.

The x = 0.9 sample shows the lowest return loss (RL) of -45dB and the optimized EM absorption characteristics for the X band (8-12GHz) satisfying RL < -15dB in the 8-13GHz range. The x = 0.8 sample shows excellent Ku band band (12-18GHz) absorption performance, satisfying RL < -19dB in the 11-18GHz range.

The features, structures, effects, etc. described in the foregoing embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to only one embodiment. Furthermore, the features, structures, effects, etc. illustrated in each embodiment can be combined or modified with respect to other embodiments by those skilled in the art in the field to which the embodiments belong. Therefore, contents related to these combinations and variations should be construed as being included in the scope of the present invention.

In addition, although the embodiments have been described above, these are merely examples and do not limit the present invention, and those skilled in the art to which the present invention belongs will be able to know that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiment. For example, each component specifically shown in the embodiments can be modified and implemented. And differences related to these variations and applications should be construed as being included in the scope of the present invention as defined in the appended claims.

Claims (8)

Hexagonal ferrite represented by SrFe _12-2x Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.5, or 2.0). delete Hexagonal ferrite represented by SrFe _12-2x Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.5, or 2.0); and
A radio wave absorber composition comprising a polymer. According to claim 3,
The radio wave absorber composition, characterized in that the polymer is included in 5 wt% to 20 wt% based on the total weight of the radio wave absorber composition. According to claim 3,
The radio wave absorber composition, characterized in that the polymer is an epoxy. delete A radio wave absorbing sheet comprising hexagonal ferrite represented by SrFe _12-2x Zn _x Zr _x O ₁₉ (x = 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.5, or 2.0). delete