Magnetic material for antennas, antenna, and wireless communication device

1. A magnetic material for antennas, comprising:

a M-type hexagonal ferrite represented by the following general formula (1) as a main phase:

MA.Fe 12-x .MB x .O 19   (1)

where MA is at least one selected from the group consisting of Sr and Ba,

MB is MC or MD,

MC is at least one selected from the group consisting of Al, Cr, Sc and In,

MD is an equivalent mixture of at least one selected from the group consisting of Ti, Sn and Zr and at least one selected from the group consisting of Ni, Zn, Mn, Mg, Cu and Co,

X is a number from 1 to 5; and

at least one compound selected from the group consisting of 0.1-3% by mass of SiO 2 , 0.5-5% by mass of CaO, and 0.5-8% by mass of Bi 2 O 3 ,

wherein an average crystal particle diameter of a sintered compact sample surface of the magnetic material after etching by concentrated hydrochloric acid is equal to or greater than 20 μm as determined by observation with a scanning electron microscope, and

a natural resonance frequency f0(n) of the magnetic material is configured to be equal to or greater than 5 GHz and a magnetic domain wall resonance frequency f0(d·w) of the magnetic material is configured to be equal to or smaller than 0.8 GHz.

2. The magnetic material for antennas according to claim 1 , wherein a real part of a complex relative permeability at 2 GHz is equal to or greater than 1.2, and a magnetic loss at 2 GHz is equal to or smaller than 0.01.

3. The magnetic material for antennas according to claim 1 , wherein a real part of a complex relative permittivity at 2 GHz is equal to or smaller than 30, and a dielectric loss at 2 GHz is equal to or smaller than 0.05.

4. The magnetic material for antennas according to claim 2 , wherein a real part of a complex relative permittivity at 2 GHz is equal to or smaller than 30, and a dielectric loss at 2 GHz is equal to or smaller than 0.05.

5. An antenna comprising:

a base substance comprising the magnetic material for antennas according to claim 1 ;

a conductor that is provided on a surface or inside of the base substance; and

a feed terminal that is connected to the conductor and supplies an electrical energy to the conductor.

6. An antenna according to claim 5 , wherein the base substance is a sintered compact with a void ratio of 1-40%.

7. A wireless terminal device comprising the antenna according to claim 5 .

8. A wireless terminal device comprising the antenna according to claim 6 .

9. The magnetic material for antennas according to claim 1 , wherein the average crystal particle diameter is in the range of 20 μm to 50 μm.