Inductor core, electronic pen, and input device

1. An inductor core comprising:

a magnetic main body having a pillar shape and comprised of a magnetic material, wherein

the magnetic main body includes:

an inclined portion including an inclined surface that constitutes an outer circumferential surface of a truncated cone having an outer diameter increasing from one end of the magnetic main body toward the other end; and

a straight body portion that is coaxial with the inclined portion and includes an outer peripheral surface that constitutes an outer circumferential surface of a cylindrical column body extending from the other end toward the one end, the straight body portion being connected to the inclined portion, and

an arithmetic mean roughness Ra of an outer peripheral surface of the straight body portion located at or around the other end is smaller than an arithmetic mean roughness Ra of an outer peripheral surface of the straight body portion located at or around the inclined portion.

2. The inductor core according to claim 1 , wherein

the arithmetic mean roughness Ra of the outer peripheral surface of the straight body portion located at or around the inclined portion is equal to or less than 6 μm.

3. The inductor core according to claim 1 , wherein

a root mean square roughness Rq of the outer peripheral surface of the straight body portion located at or around the other end is smaller than a root mean square roughness Rq of the outer peripheral surface of the straight body portion located at or around the inclined portion.

4. The inductor core according to claim 3 , wherein

the root mean square roughness Rq of the outer peripheral surface of the straight body portion located at or around the inclined portion is not more than 10 μm.

5. The inductor core according to claim 1 , wherein

the magnetic main body is made out of ceramic containing, as a main constituent, ferrite comprised of an oxide of Fe, Zn, Ni, and Cu, and

a coefficient of variation CV of an average crystal grain size of the ceramic expressed as Equation (1) stated below is not less than 0.08 and not more than 0.3,

CV=σ/ x   (1)

where x is an average value of the average crystal grain size of the ceramic, and σ is a standard deviation of the average crystal grain size of the ceramic.

6. The inductor core according to claim 5 , wherein

a kurtosis Ku of the average crystal grain size is equal to or more than 0.

7. The inductor core according to claim 5 , wherein

a skewness Sk of the average crystal grain size is equal to or more than 0.

8. The inductor core according to claim 5 , wherein

a composition in 100 mol % obtained by adding up the main constituents includes Fe of not less than 49 mol % and not more than 50 mol % on a Fe 2 O 3 basis, Zn of not less than 29 mol % and not more than 34 mol % on a ZnO basis, Ni of not less than 10 mol % and not more than 12.5 mol % on a NiO basis, and Cu of not less than 4 mol % and not more than 9 mol % on a CuO basis.

9. The inductor core according to claim 8 , comprising

at least any of an oxide of Mo and an oxide of Bi, wherein

a content of the oxide of Mo with respect to 100 parts by mass of the main constituent is not less than 0.01 parts by mass and not more than 0.2 parts by mass on a MoO 3 basis, or

a content of the oxide of Bi with respect to 100 parts by mass of the main constituent is not less than 0.01 parts by mass and not more than 0.2 parts by mass on a Bi 2 O 3 basis.

10. The inductor core according to claim 8 , comprising

at least any of an oxide of Mn and an oxide of Ti, wherein

a content of the oxide of Mn with respect to 100 parts by mass of the main constituent is not less than 0.01 parts by mass and not more than 0.3 parts by mass on a MnO 2 basis, or

a content of the oxide of Ti with respect to 100 parts by mass of the main constituent is not less than 0.01 parts by mass and not more than 0.2 parts by mass on a TiO 2 basis.

11. The inductor core according to claim 8 , comprising

an oxide of Zr, wherein

a content of the oxide of Zr with respect to 100 parts by mass of the main constituent is not less than 0.01 parts by mass and not more than 0.2 parts by mass on a ZrO 2 basis.

12. The inductor core according to claim 8 , comprising

an oxide of Cr, wherein

a content of the oxide of Cr with respect to 100 parts by mass of the main constituent is not less than 0.02 parts by mass and not more than 0.3 parts by mass on a Cr 2 O 3 basis.

13. The inductor core according to claim 8 , wherein

at least the inclined portion contains Mo, and

a grain boundary layer interposed between the ferrite crystals adjacent to each other contains more Mo than that contained in grains of a ferrite crystal.

14. The inductor core according to claim 8 , wherein

in at least a portion of a ferrite crystal, a content of Fe at a center portion of the ferrite crystal is greater than a content of Fe at an outer edge portion of the ferrite crystal.

15. The inductor core according to claim 14 , wherein

a difference between the content of Fe at the center portion and the content of Fe at the outer edge portion is not less than 1.3 mass % and not more than 4.0 mass %.

16. The inductor core according to claim 8 , wherein

I 2 /I 1 is not less than 0.29 and not more than 0.38, where I 1 is an X-ray diffraction peak intensity at a diffraction angle (2θ) falling within a range of not less than 35° and not more than 36° and obtained through X-ray diffraction using a Cu-Kα line, and I 2 is an X-ray diffraction peak intensity at a diffraction angle (2θ) falling within a range of not less than 29.5° and not more than 30.5°.

17. The inductor core according to claim 16 , wherein

a half width of the X-ray diffraction peak intensity I 1 is not less than 0.05 and not more than 0.35.

18. The inductor core according to claim 16 , wherein

I 3 /I 1 is equal to or less than 0.14, where I 3 is an X-ray diffraction peak intensity at a diffraction angle (2θ) falling within a range of not less than 42° and not more than 43°.

19. An electronic pen comprising:

a housing including an opening;

a writing unit that can be used to write on a target writing surface; and

the inductor core according to claim 1 , wherein

the writing unit is disposed along a central axis of the housing, and

the inductor core is disposed alongside the writing unit within the housing.

20. An input device comprising:

the electronic pen according to claim 19 ; and

a position detection device including a sensor configured to detect a position at which the electronic pen approaches.