Patent Publication Number: US-7714793-B2

Title: High-frequency magnetic material and antenna system using thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-243899, filed on Sep. 20, 2007, the entire contents of which are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to a high-frequency magnetic material and an antenna system using thereof. 
   BACKGROUND OF THE INVENTION 
   High frequencies such as a GHz band are used as a frequency band of radio waves used by current mobile devices. However, for example, if a metal is present near an antenna of a mobile device when the antenna radiates electromagnetic waves, radiation of electromagnetic waves is disturbed due to an induced current generated in the metal. Thus, by arranging a high-frequency magnetic material (a material that exhibits high permeability in a high-frequency region) near the antenna to suppress generation of an unnecessary induced current, stability in radio frequency communication in a high-frequency region is believed to be achievable. 
   Metals or alloys having Fe, Co, Ni or the like as main components, or oxides thereof are used as ordinary high permeability members. High permeability members of metal or alloy are not appropriate as high-frequency magnetic materials because transmission losses caused by an eddy current of radio waves become more pronounced as the frequency of radio waves increases. 
   Magnetic materials of oxide exemplified by ferrite, on the other hand, suppress transmission losses caused by an eddy current because of high resistivity, but the resonance frequencies are several hundred MHz and transmission losses caused by resonance in a high-frequency region higher than these frequencies become more pronounced and therefore, magnetic materials of oxide are not appropriate as high-frequency magnetic materials either. 
   Thus, development of a high-frequency magnetic material superior in magnetic properties in a high-frequency region up to the GHz band is demanded. A superior high-frequency magnetic material is a material that has high resistivity, a large real part μ′ of permeability, and a small imaginary part μ″ of permeability showing a loss component of permeability, that is, small “μ″/μ′” in a high-frequency region. 
   As an attempt to produce such a high-frequency magnetic material, a high permeability nano-granular material having a granular structure using a thin film technology such as a sputtering method has been made. Here, the granular structure is a structure in which magnetic metal fine particles are dispersed in an insulating matrix and it has been confirmed that such a structure exhibits superior properties also in a high-frequency region (for example, S. Ohmura et al., “High-frequency magnetic properties in metal-nonmetal granular films”, Journal of Applied Physics 79(8) pp. 5130-5135 (1996)). However, with the granular structure, it is difficult to make permeability still higher by improving volume percentage of magnetic metal fine particles in a high-frequency magnetic material. 
   Also, a high permeability material in a high frequency region having a columnar structure has been produced whose volume percentage of magnetic metals is further improved from that of the granular structure. This is a structure in which magnetic metals in a columnar shape are dispersed in an insulating matrix and it has been confirmed that this structure exhibits higher permeability than the granular structure (for example, N. Hayashi et al., “Soft Magnetic Properties and Microstructure of Ni 81 Fe 19 /(Fe 70 CO 30 ) 99 (Al 2 O 3 ) 1 ) Films Deposited by Ion Beam Sputtering”, Transaction of the Materials Research Society of Japan 29 [4] pp. 1611-1614 (2004)). 
   However, materials having the columnar structure have large magnetic anisotropic dispersion caused by a disturbance of crystalline orientation or the like and thus, there is a problem that a loss component μ″ in a high-frequency region is large and μ″/μ′ is also large. 
   SUMMARY OF THE INVENTION 
   A high-frequency magnetic material in an aspect of the present invention includes a substrate and a composite magnetic film formed on the substrate and made of a magnetic phase forming a plurality of columnar bodies whose longitudinal direction is directed in a direction perpendicular to a surface of the substrate and an insulator phase filling gaps of the columnar bodies, wherein the magnetic phase contains Fe and B (boron) and at least one of Nb, Zr, and Hf, and is amorphous, and has in-plane uniaxial anisotropy of Hk2/Hk1≧3 and Hk2≧3.98×10 3  A/m when a minimal anisotropic magnetic field in a plane parallel to the surface of the substrate is Hk1 and a maximal anisotropic magnetic field is Hk2. 
   An antenna system in an aspect of the present invention includes a feed terminal, an antenna element whose one end is connected to the feed terminal, and a high-frequency magnetic material for suppressing transmission losses of electromagnetic waves radiated from the antenna element, wherein the high-frequency magnetic material includes a substrate and a composite magnetic film formed on the substrate and made of a magnetic phase forming a plurality of columnar bodies whose longitudinal direction is directed in a direction perpendicular to a surface of the substrate and an insulator phase filling gaps of the columnar bodies and the magnetic phase contains Fe and B and at least one of Nb, Zr and Hf, and is amorphous, and has in-plane uniaxial anisotropy of Hk2/Hk1≧3 and Hk2≧3.98×10 3  A/m when the minimal anisotropic magnetic field in a plane parallel to the surface of the substrate is Hk1 and the maximal anisotropic magnetic field is Hk2. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view and a top view of a high-frequency magnetic material in a first embodiment. 
       FIG. 2  is a graph showing an applied magnetic field dependence of magnetization. 
       FIG. 3  is a sectional view of a high-frequency magnetic material in a second embodiment. 
       FIG. 4  is a perspective view of an antenna system in a third embodiment. 
       FIG. 5  is a sectional view of the antenna system in the third embodiment. 
       FIG. 6  is a graph showing an X ray diffraction pattern on a surface of a composite magnetic material in Example 1. 
       FIG. 7  is a graph showing VSM measurement results in Example 1. 
       FIG. 8  is a graph showing high-frequency characteristic measurement results in Example 1. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The inventors found that by containing Fe and B and at least one of Nb, Zr and Hf in a magnetic phase, the magnetic phase can be made amorphous with a small amount of added elements, magnetic anisotropic dispersion can be suppressed while maintaining high permeability and also the loss component of permeability can be reduced more than a composite magnetic film having a crystalline columnar structure in a high-frequency region. The present invention is completed based on the above findings made by the inventors. 
   Amorphous herein refers to a state in which the half width of the strongest peak of Fe in X ray diffraction using CuKα rays is 3.0 or more. 
   First Embodiment 
   A high-frequency magnetic material in the first embodiment of the present invention includes a substrate and a composite magnetic film formed on the substrate and made of a magnetic phase forming a plurality of columnar bodies whose longitudinal direction is directed in a direction perpendicular to a surface of the substrate and an insulator phase filling gaps of the columnar bodies. In addition, the magnetic phase contains Fe and B. And the magnetic phase also contains at least one of Nb, Zr and Hf. And the magnetic phase is amorphous, and has in-plane uniaxial anisotropy of Hk2/Hk1≧3 and Hk2≧3.98×10 3  A/m when a minimal anisotropic magnetic field in a plane parallel to the surface of the substrate is Hk1 and a maximal anisotropic magnetic field is Hk2. 
     FIG. 1  is a diagram showing the structure of a high-frequency magnetic material in the present embodiment.  FIG. 1A  is a perspective view and  FIG. 1B  is a top view. 
   A high-frequency magnetic material  10  illustrated in  FIG. 1  has a magnetic phase  14  forming on a substrate  12  a plurality of columnar bodies whose longitudinal direction is directed in the direction perpendicular to the surface of the substrate  12 . The magnetic phase  14  contains at least one of Nb, Zr, and Hf, and Fe and B. In addition, the magnetic phase  14  is amorphous. 
   Nb, Zr, and Hf produce an effect of raising the crystallization temperature of Fe. B produces an effect of making Fe amorphous by entering space between lattices of Fe. Thus, by adding both elements to Fe, Fe can be made amorphous efficiently with a small amount of added elements. If the amount of added elements is small, the proportion of Fe increases so that permeability can be made higher. Also, if the amount of added elements is small, disturbances of the columnar structure itself can be suppressed so that a loss component of permeability can be reduced. In addition, by making the magnetic phase  14  amorphous, magnetic anisotropic dispersion can be suppressed while maintaining high permeability and also the loss component of permeability can be reduced more than a composite magnetic film having a crystalline columnar structure. 
   A ratio x of a total of Nb, Zr, and Hf contained in the magnetic phase  14  is preferably 1 at %≦x≦7 at %. If x is less than 1 at %, the effect of raising the crystallization temperature of Fe will be small, making Fe less likely to be amorphous. If x is more than 7 at %, the crystallization temperature of Fe will be constant, causing a possibility of lower permeability due to a smaller proportion of Fe despite more addition of metal. 
   A ratio y of B contained in the magnetic phase  14  is preferably 5 at %≦y≦20 at %. If y is less than 5 at %, Fe is less likely to become amorphous. If y is more than 20 at %, the proportion of Fe becomes smaller, leading to lower permeability or an increase in loss component of permeability due to disturbances of the columnar structure. 
   Moreover, if a metal becomes amorphous, electric resistivity can be made larger than that of the crystalline metal. That is, by making the magnetic phase amorphous columnar bodies, an excellent high-frequency magnetic material showing high permeability, low loss, and high resistivity in a high-frequency region can be produced. 
   As shown in  FIG. 1A  and  FIG. 1B , the high-frequency magnetic material  10  has in-plane uniaxial anisotropy of Hk2/Hk1≧3 and Hk2≧3.98×10 3  A/m (=50 Oe) when the minimal anisotropic magnetic field in a plane parallel to the surface of the substrate is Hk1 and the maximal anisotropic magnetic field is Hk2. 
   A high-frequency magnetic material according to the present embodiment can reduce the loss component of permeability in a high-frequency region by including in-plane uniaxial anisotropy in the above range. 
   Why the loss component of permeability in a high-frequency region is enabled to be reduced in a high-frequency region by having in-plane uniaxial anisotropy can be considered as follows: The maximal anisotropic magnetic field and a resonance frequency of permeability are in a proportional relationship and the resonance frequency of 1 GHz or more can be achieved by setting Hk2≧3.98×10 3  A/m. Then, in order to attain Hk2≧3.98×10 3  A/m, it is effective to provide in-plane uniaxial anisotropy satisfying Hk2/Hk1≧3. By having in-plane uniaxial anisotropy, as described above, the maximal anisotropic magnetic field can be made larger than when magnetic properties are isotropic and, as a result, μ″/μ′ in a high-frequency region can be made smaller. 
   If the magnetic phase contains at least one of Nb, Zr and Hf, and Fe and B, is amorphous, and includes in-plane uniaxial anisotropy satisfying Hk2/Hk1≧3 and Hk2≧3.98×10 3  A/m when the minimal anisotropic magnetic field in a plane parallel to the surface of the substrate is Hk1 and the maximal anisotropic magnetic field is Hk2, as described above, the loss component of permeability in a high-frequency region can greatly be reduced compared with a conventional magnetic material. 
     FIG. 1  exemplifies an elliptical columnar body whose section perpendicular to the longitudinal direction of the columnar body of the magnetic phase  14  has an elliptical shape, but in addition to the elliptical columnar body, other shapes such as a cylindrical body, a square columnar body, a hexagonal columnar body, and an octagonal columnar body are also allowed. 
   An insulator phase  16  is formed between these columnar bodies. A portion combining the magnetic phase  14  and the insulator phase  16  is called a composite magnetic film  18 . 
   It is preferable that 5 nm≦D≦20 nm and D/S≧4 be satisfied when an average value of a diameter at a bottom of one columnar body in the magnetic phase  14  is D and that of an interval between the columnar bodies is S ( FIG. 1B ). Here, arbitrary two locations on the surface parallel to the substrate of the high-frequency magnetic material are observed using a transmission electron microscope (of a magnification of 400,000 times). Then, the maximal and minimal diameters at each bottom of all columnar bodies included in a range corresponding to 100 nm in four directions from the center of each observation photograph are measured and the average value of all these values is set as D. If apparently a columnar body formed by a plurality of columnar bodies being coalesced is present, such a columnar body shall be excluded from measurement. A total of 20 columnar bodies, 10 from each location, is randomly selected from 100 nm in four directions from the center of the observation photograph at two locations described above and intervals between each columnar body and adjacent columnar bodies are measured to set the average value of all measured values as S. 
   If D is smaller than 5 nm, it becomes more difficult to form a columnar body, leading to a lower volume percentage of the magnetic phase  14  in a high-frequency magnetic material and lower permeability. If D is larger than 20 nm, coercive force becomes larger, leading to an increase in loss of permeability. If D/S is smaller than 4, the volume percentage of the magnetic phase  14  may decrease, leading to lower permeability. 
   The ratio of the height to the diameter (aspect ratio) of a columnar body is preferably 5 or more. Here, the diameter is the average value D of diameters at the bottom of columnar bodies. Also, arbitrary two locations perpendicular to the substrate of the high-frequency magnetic material are observed using a transmission electron microscope (of a magnification of 400,000 times). Then, a total of 20 columnar bodies, 10 from each location, is selected in descending order of height (length) in each observation photograph to define the average value of heights thereof as the height of the columnar bodies. 
   If the aspect ratio is smaller than 5, the insulator phase  16  will be present also between bottoms of columns, leading to lower permeability due to lower volume percentage of the magnetic phase  14 .  FIG. 1A  illustrates only one columnar body in a direction perpendicular to the surface of the substrate  12 . However, a plurality of columnar bodies may actually be arranged in the direction perpendicular to the surface of the substrate  12 , sandwiching the insulator phase  16  in the longitudinal direction of the columnar bodies. 
   In the composite magnetic film  18 , a ratio P of an area occupied by the magnetic phase  14  in a plane parallel to the surface of the substrate  12  is preferably 75%≦P≦95%. If P is less than 75%, the volume percentage of the magnetic phase  14  may decrease, leading to lower permeability. If P is more than 95%, columnar bodies may condense to make D larger than 20 nm, increasing the loss of permeability, as described above. 
   If the magnetic phase  14  is denoted as M, the insulator phase  16  as I, and the composite magnetic film  18  as M z I (1−z) , 0.80≦z≦0.95 is preferably satisfied, that is, the ratio of the magnetic phase occupied in the composite magnetic film is preferably 80 mol % or more and 95 mol % or less. If the magnetic phase  14  is less than 80 mol %, the volume percentage of the magnetic phase  14  may decrease to build a granular structure, leading to lower permeability. If the magnetic phase  14  is more than 95 mol %, columnar bodies may condense to make D larger than 20 nm, increasing the loss of permeability, as described above. 
   A high-frequency magnetic material according to the present embodiment can be manufactured by forming a composite magnetic film by the sputtering method, electron-beam evaporation method or the like on a substrate. By rotating the substrate and controlling film formation conditions, magnetic in-plane uniaxial anisotropy in a plane parallel to the surface of the substrate can effectively be provided to the composite magnetic film formed on the substrate. 
   For example, plastics such as polyimide, inorganic material such as SiO 2 , Al 2 O 3 , MgO, Si, and glass can be used as a substrate according to the present embodiment. However, the material of the substrate is not limited to these materials. 
   As shown in  FIG. 1 , the magnetic phase in the present embodiment has a structure of columnar bodies whose longitudinal direction is directed in the direction perpendicular to the surface of the substrate. However, longitudinal direction of columnar bodies may partially be permitted to tilt at an angle of ±30°, preferably ±10° with respect to the direction perpendicular to the surface of the substrate. 
   That columnar bodies of the magnetic phase  14  are amorphous can be determined from X ray diffraction patterns and electron diffraction patterns. In X ray diffraction patterns, instead of sharp strong peaks like those of a crystal, broad weak peaks appear. In electron diffraction patterns, instead of distinct spots, halo rings appear. As described above, amorphous herein refers to a state in which the half width of the strongest peak of Fe in X ray diffraction using CuKα rays is 3.0 or more. 
   Particularly, a half width F is preferably 3.5≦F≦5.5. This is an area of amorphous much closer to crystalline. If the magnetic phase is crystalline, magnetic anisotropy can be provided more easily and the resonance frequency becomes higher, but due to disturbances of crystalline orientation (that is, polycrystal), magnetic anisotropic dispersion arises, increasing the loss component of permeability (imaginary part μ″). If the magnetic phase is amorphous, magnetic anisotropic dispersion resulting from disturbances of crystalline orientation is extremely small because there is no crystalline orientation, but due to difficulty of providing magnetic anisotropy, the resonance frequency may decrease, leading to an increase in loss component of permeability in a high-frequency region. By making the magnetic phase amorphous much closer to crystalline, a material having both a high resonance frequency, which is an advantage of crystalline, and small magnetic anisotropic dispersion, which is an advantage of amorphous, and whose loss component of permeability in a high-frequency region is very small can be produced. In the present invention, by controlling film formation conditions by adjusting the amounts of added elements x and y in the above ranges, an excellent high-frequency magnetic material whose loss component of permeability is small can be produced. If F is smaller than 3.5, crystallization proceeds and, if F is larger than 5.5, amorphization proceeds. In both cases, an increase in loss component of permeability in a high-frequency region could be caused. 
   It is preferable that the magnetic phase contain Co to further increase permeability and the ratio of Co to the whole magnetic phase is preferably 20 at % or more and 40 at % or less. 
   As shown in  FIG. 1 , the insulator phase in the present embodiment fills gaps of columnar bodies of the magnetic phase  14 . In terms of suppressing transmission losses caused by an eddy current, the material of the insulator phase  16  preferably has electric resistivity of 1×10 2  Ωcm or more at room temperature. 
   The material of the insulator phase  16  may include oxide, nitride, carbide, and fluoride of metal selected, for example, from a group consisting of Mg, Al, Si, Ca, Cr, Ti, Zr, Ba, Sr, Zn, Mn, Hf, and rare earth elements (including Y). In terms of ease and costs of film formation, particularly oxide, among others, silicon oxide and aluminum oxide are preferable. 
   The insulator phase  16  permits inclusion of 30 mol % or less of magnetic metal elements. If the amount of magnetic metal elements exceeds 30 mol %, electric resistivity of the insulator phase  16  may decrease, leading to reduced magnetic properties of the whole composite magnetic film. 
   Next, magnetic in-plane uniaxial anisotropy of a composite magnetic film according to the present embodiment will be described. The composite magnetic film  18  shown in  FIG. 1  has the minimal anisotropic magnetic field Hk1 in a plane parallel to the surface of the substrate  12  and the maximal anisotropic magnetic field Hk2 in a direction perpendicular to Hk1 and has magnetic in-plane uniaxial anisotropy satisfying Hk2/Hk1≧3 and Hk2≧3.98×10 3  A/m (=50 Oe). 
   By providing uniaxial anisotropy, the maximal anisotropic magnetic field can be made larger than when magnetic properties are isotropic, making it easier to obtain an anisotropic magnetic field of 3.98×10 3  A/m or more. The maximal anisotropic magnetic field and the resonance frequency of permeability are in a proportional relationship and setting Hk2≧3.98×10 3  A/m makes it easier to attain the resonance frequency of 1 GHz or more. In order to attain Hk2≧3.98×10 3  A/m, it is effective to provide uniaxial anisotropy satisfying Hk2/Hk1≧3. By providing uniaxial anisotropy and making the maximal anisotropic magnetic field larger, as described above, μ″/μ′ in a high-frequency region can be made smaller. 
   As shown in  FIG. 2 , Hk (Hk1 and Hk2) is defined herein as a magnetic field at the intersection of a tangent in a magnetic field in which the amount of magnetization changes to an applied magnetic field is the largest (≧0) and that in a magnetic field in which the magnetization amount of changes is the smallest in the first quadrant (magnetization&gt;0, applied magnetic field&gt;0) of a magnetization curve. 
   Such magnetic anisotropy can be realized, for example, by making the diameter in the direction corresponding to the anisotropic magnetic field Hk1 of a columnar body on the surface of the composite magnetic film  18  longer and that in the direction corresponding to the anisotropic magnetic field Hk2 shorter. 
   Magnetic anisotropy can also be provided by changing the amount of magnetic elements in the insulator phase  16 . Magnetic anisotropy can be realized, for example, by making columnar bodies in the direction corresponding to the anisotropic magnetic field Hk1 on the surface of the composite magnetic film  18  have more magnetic elements in the insulator phase  16  than those in the direction corresponding to the anisotropic magnetic field Hk2. 
   It is also possible to provide magnetic anisotropy by making the interatomic distance of Fe in the direction corresponding to the anisotropic magnetic field Hk1 on the surface of the composite magnetic film  18  longer than that of Fe in the direction corresponding to the anisotropic magnetic field Hk2. 
   The high-frequency magnetic material  10  according to the present embodiment permits formation of a thin film layer containing a different material from that of the composite magnetic film  18  between the substrate  12  and the composite magnetic film  18 . When the composite magnetic film  18  is formed on such a thin film layer, the high-frequency magnetic material  10  having further improved magnetic properties can be obtained, for example, by being able to control the diameter of columnar bodies in the magnetic phase  14  of the composite magnetic film  18  and reducing disturbances of a magnetic structure at an interface between the substrate  12  and the composite magnetic film  18 . 
   The thin film layer is preferably selected from Ni, Fe, Cu, Ta, Cr, Co, Zr, Nb, Ru, Ti, Hf, W, Au, or an alloy thereof, or an oxide such as SiO 2  and Al 2 O 3 . 
   Then, the thin film layer preferably has a thickness of 50 nm or less. If the thickness of the thin film layer exceeds 50 nm, there is a possibility that the volume percentage of the magnetic phase  14  in the high-frequency magnetic material decreases, leading to lower permeability. 
   The high-frequency magnetic material preferably has high resistivity in a high-frequency region to suppress transmission losses caused by an eddy current. It is effective to cut a slit in the material to make resistivity of the high-frequency magnetic material higher. Generation of an eddy current can be suppressed by cutting a slit at intervals of 100 to 1000 μm and making the high-frequency magnetic material finer. 
   Second Embodiment 
   A high-frequency magnetic material according to the second embodiment of the present invention is the same as that according to the first embodiment except that the composite magnetic film further includes an insulator layer parallel to a substrate. Therefore, a description of portions that overlap with those of the first embodiment is omitted below. 
     FIG. 3  is a sectional view of a high-frequency magnetic material in the present embodiment. As shown in  FIG. 3 , the high-frequency magnetic material in the present embodiment has a structure in which at least two layers of the composite magnetic film  18  are laminated on the substrate  12  and an insulator layer  20  is formed between these composite magnetic films  18 . 
   By causing the insulator layer  20  to lie between two or more layers of the composite magnetic film  18 , that is, by making the film thicker by separating the composite magnetic film  18  in the thickness direction through the insulator layer  20 , it becomes possible to reduce an influence of a demagnetizing field generated when the composite magnetic film  18  is made thicker without causing the insulator layer  20  to lie in the composite magnetic film  18  and to improve magnetic properties of the whole high-frequency magnetic material  10 . Also, disturbances of the structure in the thickness direction that could occur when the composite magnetic film  18  is made thicker can also be avoided.  FIG. 3  shows one layer of the insulator layer  20 , but a plurality of insulator layers may be present. 
   The insulator layer  20  is preferably made of at least one selected, for example, from a group of oxide, nitride, carbide, and fluoride of metal selected from a group of Mg, Al, Si, Ca, Cr, Ti, Zr, Ba, Sr, Zn, Mn, Hf, and rare earth elements (including Y). Particularly, it is preferable to select a material for the insulator layer  20  that is of the same kind as that of the insulator phase  16  constituting the composite magnetic film  18 . 
   The insulator layer  20  has a thickness of 5 nm or more and 100 nm or less, preferably 50 nm or less. If the insulator layer  20  has the thickness exceeding 100 nm, the volume percentage of the magnetic phase in the high-frequency magnetic material  10  decreases, leading to lower permeability. If the insulator layer  20  has the thickness below 5 nm, there is a possibility that an influence of a demagnetizing field becomes more pronounced because magnetic coupling between the composite magnetic films  18  is not cut off. 
   Third Embodiment 
   An antenna system according to the third embodiment of the present invention includes a feed terminal, an antenna element whose one end is connected to the feed terminal, and a high-frequency magnetic material for suppressing transmission losses of electromagnetic waves radiated from the antenna element. Then, the high-frequency magnetic material is the high-frequency magnetic material described in the first embodiment or the second embodiment. Therefore, a description of the high-frequency magnetic material is omitted below due to an overlap with that of the high-frequency magnetic material in the first embodiment or second embodiment. 
     FIG. 4  is a perspective view of an antenna system according to the present embodiment and  FIG. 5  is a sectional view thereof. The high-frequency magnetic material  10  is provided between antenna elements  24  whose one end is connected to a feed terminal  22  and a wired substrate  26 . The wired substrate  26  is, for example, a wired substrate of a mobile device and is enclosed, for example, by a metallic chassis. 
   When an antenna of a mobile device radiates electromagnetic waves, for example, radiation of electromagnetic waves is disturbed by an induced current generated in a metal when the antenna and a metal such as a chassis of the mobile device come closer than a certain distance. However, if a high-frequency magnetic material is arranged near the antenna, no induced current is generated even if the antenna and the metal such as a chassis are brought closer so that radio frequency communication can be stabilized and the mobile device can be made smaller. 
   By inserting the high-frequency magnetic material  10  between the two antenna elements  24  sandwiching the feed terminal  22  and a wired substrate  9 , like the present embodiment, an induced current generated in the wired substrate  26  is suppressed when electromagnetic waves are radiated by the antenna elements  24  so that radiation efficiency of the antenna system can be improved. 
   Embodiments of the present invention have been described above with reference to concrete examples. According to these embodiments, an excellent high-frequency magnetic material having a smaller ratio (μ″/μ′) of the real part μ′ of permeability and the imaginary part μ″ of permeability in a high-frequency region and an antenna system using thereof can be provided. The above embodiments are shown strictly as examples and do not limit the present invention. Though descriptions of parts in a high-frequency magnetic material, an antenna system using thereof and the like that were not directly necessary to describe the present invention were omitted when describing these embodiments, necessary components related to the high-frequency magnetic material or the antenna device using thereof can appropriately be selected and used. 
   In addition, all high-frequency magnetic materials equipped with components of the present invention and whose design can appropriately be modified by a person skilled in the art and antenna devices using thereof are included in the scope of the present invention. The scope of the present invention is defined by appended claims and equivalents thereof. 
   EXAMPLES 
   Examples of the present invention will be described below in detail. 
   Example 1 
   An opposed type magnetron sputter film formation apparatus was used. Fe 57.1 Co 24.5 Nb 3.4 B 15 —SiO 2  (the ratio x of Nb in the magnetic phase is 3.4 at %, the ratio y of B is 15 at %, and FeCoNbB to be the magnetic phase is 93 mol %, that is, z=0.93) was used as the target. A rotating holder was arranged inside a chamber and an SiO 2  substrate was fixed onto the holder. While rotating the substrate at 10 rpm, sputtered particles from the target were caused to deposit onto the substrate surface under pressure of 0.67 Pa (5×10 −3  Torr) in an Ar atmosphere inside the chamber to form a composite magnetic film having a thickness of 0.42 μm. 
   X ray diffraction measurement using CuKα rays (XRD) was made on the surface of the composite magnetic film. A measurement result is shown in  FIG. 6 . The half width F of a (110) peak of Fe near 2θ=45° is 5.04, showing that the film is in an amorphous state. 
   A plane parallel to the substrate surface of the composite magnetic film was observed under a transmission electron microscope (TEM) with two views (two photographs). The maximal and minimal diameters at the bottom of all columnar bodies included in a range corresponding to 100 nm in four directions from the center of each observation photograph were measured and an average value of all these values was calculated to obtain D=10 nm. Also, a total of 20 columnar bodies, 10 from each photograph, was randomly selected from the range corresponding to 100 nm in four directions from the center of each observation photograph and intervals between each columnar body and adjacent columnar bodies were measured and an average value of all these values was calculated to obtain S=1.1 nm. The ratio P of an area occupied by the magnetic phase was 92%. 
   A vibrating sample magnetometer (VSM) was used to measure magnetic properties (magnitude of magnetization with respect to an applied magnetic field) of the composite magnetic film in the direction parallel to the substrate rotation during film formation and in the direction perpendicular to the substrate rotation.  FIG. 7  shows results thereof. The minimal anisotropic magnetic field Hk1 in the direction parallel to the substrate rotation was 0.41×10 3  A/m and the maximal anisotropic magnetic field Hk2 in the direction perpendicular to the substrate rotation was 14.2×10 3  A/m. 
   A super-high frequency permeability measuring system PMM-9G1 manufactured by Ryowa Electronics was used to make measurement with magnetizing the composite magnetic film to the direction of the maximal anisotropic magnetic field in the range of 1 MHz to 9 GHz.  FIG. 8  shows results thereof. The real part μ′ of permeability at 1 GHz was 113.7, the imaginary part μ″ of permeability showing a loss component of permeability at 1 GHz was 2.98, and μ″/μ′ showing magnetic properties at 1 GHz was 0.026. The above measurement results are summarized in Table 1. 
   Example 2 
   Film formation and measurement were performed in the same manner as in Example 1 except that Nb was replaced by Zr. Results thereof are listed in Table 1. 
   Example 3 
   Film formation and measurement were performed in the same manner as in Example 1 except that Nb was replaced by Hf. Results thereof are listed in Table 1. 
   Example 4 
   Film formation and measurement were performed in the same manner as in Example 1 except that x=3.6 at % and y=10 at % were set. Results thereof are listed in Table 1. 
   Example 5 
   Film formation and measurement were performed in the same manner as in Example 1 except that x=1 at % and y=20 at % were set. Results thereof are listed in Table 1. 
   Example 6 
   Film formation and measurement were performed in the same manner as in Example 1 except that x=7 at % and y=5 at % were set. Results thereof are listed in Table 1. 
   Example 7 
   Film formation and measurement were performed in the same manner as in Example 1 except that x=0.5 at % and y=15 at % were set. Results thereof are listed in Table 1. 
   Example 8 
   Film formation and measurement were performed in the same manner as in Example 1 except that x=8 at % and y=15 at % were set. Results thereof are listed in Table 1. 
   Example 9 
   Film formation and measurement were performed in the same manner as in Example 1 except that y=4 at % was set. Results thereof are listed in Table 1. 
   Example 10 
   Film formation and measurement were performed in the same manner as in Example 1 except that y=22 at % was set. Results thereof are listed in Table 1. 
   Example 11 
   Film formation and measurement were performed in the same manner as in Example 1 except that z=0.80 was set. Results thereof are listed in Table 1. 
   Example 12 
   Film formation and measurement were performed in the same manner as in Example 1 except that z=0.95 was set. Results thereof are listed in Table 1. 
   Example 13 
   Film formation and measurement were performed in the same manner as in Example 1 except that z=0.97 was set. Results thereof are listed in Table 1. 
   Comparative Example 1 
   Film formation and measurement were performed in the same manner as in Example 1 except that z=0.75 was set. The magnetic phase had a granular structure, instead of the columnar structure. Results thereof are listed in Table 1. 
   Comparative Example 2 
   Film formation and measurement were performed in the same manner as in Example 1 except that x=0 at % was set. Results thereof are listed in Table 1. 
   Comparative Example 3 
   Film formation and measurement were performed in the same manner as in Example 1 except that y=0 at % was set. The magnetic phase became crystalline. Results thereof are listed in Table 1. 
   Comparative Example 4 
   Film formation and measurement were performed in the same manner as in Example 1 except that the substrate was rotated at 5 rpm in the film formation. Results thereof are listed in Table 1. 
   Comparative Example 5 
   Film formation and measurement were performed in the same manner as in Example 1 except that the pressure was changed to 0.27 Pa (2×10 −3  Torr) in an Ar atmosphere inside the chamber in the film formation. Results thereof are listed in Table 1. 
   
     
       
         
             
             
             
             
             
             
             
             
             
           
             
               TABLE 1 
             
           
          
             
                 
             
             
                 
                 
                 
                 
                 
                 
               D AVE. 
               S AVE. 
                 
             
             
                 
                 
                 
               x 
               y 
                 
               VALUE 
               VALUE 
                 
             
             
                 
               STRUCTURE 
               CRYSTALLINITY 
               [at %] 
               [at %] 
               z 
               [nm] 
               [nm] 
               D/S 
             
             
                 
             
             
               EXAMPLE 1 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.93 
               10 
               1.1 
               9.1 
             
             
               EXAMPLE 2 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 3 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.93 
               10 
               1.1 
               9.1 
             
             
               EXAMPLE 4 
               COLUMNAR 
               AMORPHOUS 
               3.6 
               10 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 5 
               COLUMNAR 
               AMORPHOUS 
               1 
               20 
               0.93 
               11 
               1.2 
               9.2 
             
             
               EXAMPLE 6 
               COLUMNAR 
               AMORPHOUS 
               7 
               5 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 7 
               COLUMNAR 
               AMORPHOUS 
               0.5 
               15 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 8 
               COLUMNAR 
               AMORPHOUS 
               8 
               15 
               0.93 
               9 
               1.1 
               8.2 
             
             
               EXAMPLE 9 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               4 
               0.93 
               11 
               1.3 
               8.5 
             
             
               EXAMPLE 10 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               22 
               0.93 
               12 
               1.2 
               10.0 
             
             
               EXAMPLE 11 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.80 
               9 
               2.0 
               4.5 
             
             
               EXAMPLE 12 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.95 
               10 
               1.1 
               9.1 
             
             
               EXAMPLE 13 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.97 
               40 
               3.0 
               13.3 
             
             
               COMPARATIVE 
               GRANULAR 
               AMORPHOUS 
               3.4 
               15 
               0.75 
               30 
               10 
               3.0 
             
             
               EXAMPLE 1 
             
             
               COMPARATIVE 
               COLUMNAR 
               AMORPHOUS 
               0 
               15 
               0.93 
               10 
               1.1 
               9.1 
             
             
               EXAMPLE 2 
             
             
               COMPARATIVE 
               COLUMNAR 
               CRYSTAL 
               3.4 
               0 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 3 
             
             
               COMPARATIVE 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 4 
             
             
               COMPARATIVE 
               COLUMNAR 
               AMORPHOUS 
               3.4 
               15 
               0.93 
               10 
               1.2 
               8.3 
             
             
               EXAMPLE 5 
             
             
                 
             
          
         
         
             
             
             
             
             
             
             
             
             
             
          
             
                 
                 
               P 
                 
               Hk1 
               Hk2 
                 
                 
                 
                 
             
             
                 
                 
               [%] 
               F 
               [×10 3   A/m] 
               [×10 3   A/m] 
               Hk2/Hk1 
               μ′ 
               μ″ 
               μ″/μ′ 
             
             
                 
                 
             
             
                 
               EXAMPLE 1 
               92 
               5.04 
               0.41 
               14.2 
               34.6 
               113.7 
               2.98 
               0.026 
             
             
                 
               EXAMPLE 2 
               90 
               5.40 
               0.45 
               13.8 
               30.7 
               120.1 
               3.84 
               0.032 
             
             
                 
               EXAMPLE 3 
               92 
               5.21 
               0.45 
               14.0 
               31.1 
               119.5 
               3.94 
               0.033 
             
             
                 
               EXAMPLE 4 
               90 
               4.39 
               0.27 
               10.7 
               39.6 
               189.6 
               11.2 
               0.059 
             
             
                 
               EXAMPLE 5 
               92 
               5.43 
               0.55 
               9.98 
               18.1 
               135.5 
               8.26 
               0.061 
             
             
                 
               EXAMPLE 6 
               90 
               3.55 
               0.43 
               8.24 
               19.2 
               141.2 
               9.88 
               0.070 
             
             
                 
               EXAMPLE 7 
               90 
               5.32 
               0.61 
               7.13 
               11.7 
               129.7 
               23.3 
               0.18 
             
             
                 
               EXAMPLE 8 
               90 
               4.95 
               0.43 
               14.0 
               32.6 
               97.4 
               10.7 
               0.11 
             
             
                 
               EXAMPLE 9 
               90 
               3.40 
               0.69 
               6.37 
               9.2 
               165.0 
               29.7 
               0.18 
             
             
                 
               EXAMPLE 10 
               92 
               5.61 
               1.01 
               12.1 
               12.0 
               120.6 
               11.4 
               0.095 
             
             
                 
               EXAMPLE 11 
               80 
               5.23 
               0.48 
               13.9 
               29.0 
               109.9 
               5.17 
               0.047 
             
             
                 
               EXAMPLE 12 
               92 
               5.15 
               0.45 
               14.1 
               31.3 
               111.3 
               4.23 
               0.038 
             
             
                 
               EXAMPLE 13 
               88 
               3.95 
               1.48 
               4.46 
               3.0 
               170.8 
               34.2 
               0.20 
             
             
                 
               COMPARATIVE 
               70 
               6.40 
               1.30 
               5.88 
               4.5 
               103.3 
               64.0 
               0.62 
             
             
                 
               EXAMPLE 1 
             
             
                 
               COMPARATIVE 
               92 
               6.03 
               1.19 
               4.91 
               4.13 
               218.8 
               73.6 
               0.34 
             
             
                 
               EXAMPLE 2 
             
             
                 
               COMPARATIVE 
               90 
               0.46 
               0.98 
               8.84 
               9.0 
               200.3 
               62.1 
               0.31 
             
             
                 
               EXAMPLE 3 
             
             
                 
               COMPARATIVE 
               90 
               5.07 
               1.80 
               5.04 
               2.8 
               253.4 
               88.7 
               0.35 
             
             
                 
               EXAMPLE 4 
             
             
                 
               COMPARATIVE 
               90 
               5.19 
               3.18 
               3.18 
               1.0 
               98.0 
               91.2 
               0.93 
             
             
                 
               EXAMPLE 5 
             
             
                 
                 
             
          
         
       
     
   
   The composite magnetic film in Example 1 contains at least one of Nb, Zr, and Hf, and Fe and B (boron) and has an amorphous columnar structure and, as is evident from Table 1, the imaginary part μ″ of permeability (loss component of permeability) at 1 GHz and the ratio (μ″/μ′) of the real part of permeability and the imaginary part of permeability at 1 GHz are smaller than those of Comparative Example 1 having the granular structure, Comparative Example 2 containing none of Nb, Zr, and Hf, Comparative Example 3 containing no B and having a crystalline columnar structure, and Comparative Examples 4 and 5 satisfying Hk2/Hk1&lt;3 and Hk2&lt;3.98×10 3  A/m, showing that the composite magnetic film in Example 1 has superior magnetic properties in a high-frequency region. 
   Examples 1 to 6, 11 and 12 in which the ratio x of Nb, Zr, or Hf contained in the magnetic phase is 1 at %≦x ≦7 at % and the ratio y of B contained in the magnetic phase is 5 at %≦y≦20 at % have lower μ″/μ′ than that of Examples 7 to 10 and Comparative Examples 2 and 3 in which these values deviate from these ranges, showing that the composite magnetic film in these examples has superior magnetic properties in a high-frequency region. 
   Examples 1 to 6, 11 and 12 in which the ratio z of the magnetic phase is 0.80≦z≦0.95, 5 nm≦D≦20 nm, D/S ≧4, and 75%≦P≦95% have lower μ″/μ′ than that of Example 13 and Comparative Example 1 in which these values deviate from these ranges, showing that the composite magnetic film in these examples has superior magnetic properties in a high-frequency region. 
   Examples 1 to 6, 11 and 12 in which the half width F of the strongest peak of Fe by X ray diffraction using CuKα rays is 3.5≦F≦5.5 have lower μ″/μ′ than that of Examples 9 and 10 in which this value deviates from the range, showing that the composite magnetic film in these examples has superior magnetic properties in a high-frequency region. 
   Accordingly, an effect of the present invention has been confirmed by these examples.