Magnetic crystal for electromagnetic wave absorbing material and electromagnetic wave absorber

• US 8,072,365 B2
• Filed: 08/30/2007
• Issued: 12/06/2011
• Est. Priority Date: 09/01/2006
• Status: Active Grant

• Current Assignee: Dowa Electronics Materials Co. Ltd. (DOWA Holdings Company Limited), University of Tokyo
• Original Assignee: Dowa Electronics Materials Co. Ltd. (DOWA Holdings Company Limited), University of Tokyo
• Inventors: Ohkoshi, Shin-ichi, Sakurai, Shunsuke, Sato, Kimitaka, Sasaki, Shinya, Kuroki, Shiro, Namai, Asuka
• Primary Examiner(s): GREGORY, BERNARR E
• Application Number:
  US12/310,525
• Publication Number:
  US 20100238063A1
• Time in Patent Office: 1,559 Days
• Field of Search: 342 1- 4, 252 6251 R- 6251 C, 428/357, 428402-407, 428/411.1, 428/688, 428/689, 428/692.1, 428/693.1, 428/800, 428/826, 428/836, 428/836.1, 428/836.2, 428/846, 428/846.1, 428/846.6, 428/846.7
• US Class Current: 342/1
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: C01G 49/0018 Mixed oxides or hydroxides, C01G49/0009 takes precedence
• CPC Class Codes: C01G 49/0045 containing aluminium
• CPC Class Codes: C01P 2002/72 by d-values or two theta-values, e.g. as X-ray diagram
• CPC Class Codes: C01P 2004/04 obtained by TEM, STEM, STM or AFM
• CPC Class Codes: C01P 2004/64 Nanometer sized, i.e. from 1-100 nanometer
• CPC Class Codes: C01P 2006/42 Magnetic properties
• CPC Class Codes: C04B 2235/3217 Aluminum oxide or oxide forming salts thereof, e.g. bauxite, alpha-alumina
• CPC Class Codes: C04B 2235/3274 Ferrites
• CPC Class Codes: C04B 2235/3286 Gallium oxides, gallates, indium oxides, indates, thallium oxides, thallates or oxide forming salts thereof, e.g. zinc gallate
• CPC Class Codes: C04B 2235/5454 nanometer sized, i.e. below 100 nm
• CPC Class Codes: C04B 35/26 based on ferrites
• CPC Class Codes: C04B 35/62807 Silica or silicates
• CPC Class Codes: C04B 35/62813 Alumina or aluminates
• CPC Class Codes: C04B 35/62823 Zirconium or hafnium oxide
• CPC Class Codes: C04B 35/62886 by wet chemical techniques
• CPC Class Codes: H01F 1/344 Ferrites, e.g. having a cubic spinel structure (X2+O)(Y23+O3), e.g. magnetite Fe3O4
• CPC Class Codes: H05K 9/0075 Magnetic shielding materials

Abstract

Disclosed is a magnetic crystal for electromagnetic wave absorbing materials, having a structure of ε-M_xFe_2-xO₃ with 0<x<1, which has the same space group as that of an ε-Fe₂O₃ crystal and which is derived from an ε-Fe₂O₃ crystal by substituting a part of the Fe site therein with M. In this, M is a trivalent element having an effect of lowering the coercive force Hc of ε-Fe₂O₃ crystal by the substitution. Concretely, the element M includes Al and Ga. An electromagnetic wave absorber having a packed structure of particles having such a substituent element M-added “M-substituted ε-Fe₂O₃ crystal” as the magnetic phase may control the electromagnetic wave absorption peak frequency depending on the degree of substitution with the element M, and for example, the invention gives an electromagnetic wave absorber applicable to a 76 GHz band for on-vehicle radars.

Claims

1. A magnetic crystal for use in an electromagnetic wave absorbing materials having absorbing capability in a high frequency band of 25 to 160 GHZ, the magnetic crystal having a structure of ε

-M_xFe_2-xO₃ with 0<

x<

1, and further having the same space group as that of an ε

-Fe₂O₃ crystal and in which M is substituted for a portion of the Fe sites of the ε

-Fe₂O₃ crystal;

wherein M is a trivalent element having an effect of lowering a coercive force Hc of the magnetic oxide comprising an ε

-Fe₂O₃ crystal when M is substituted for a portion of the Fe sites of the ε

-Fe₂O₃ crystal.

2. The magnetic crystal as claimed in claim 1, wherein M is at least one of the Al, Ga and In.

3. The magnetic crystal as claimed in claim 1, wherein M is Al and x is from 0.2 to 0.8.

4. The magnetic crystal as claimed in claim 1, wherein M is Ga and x is from 0.1 to 0.8.

5. The magnetic crystal as claimed in claim 1, wherein M is In and x is from 0.01 to 0.3.

6. An electromagnetic wave absorbing material comprising a powder of particles having the magnetic crystal of claim 1 as a magnetic phase.

7. An electromagnetic wave absorber having a packed structure of particles having the magnetic crystal of claim 1 as a magnetic phase.

8. An electromagnetic wave absorber having a packed structure of particles having the magnetic crystal of claim 1 as a magnetic phase, and having an electromagnetic wave absorption peak in a band zone of from 25 to 160 GHz on a graph in which the horizontal axis indicates a frequency and the vertical axis indicates an electromagnetic wave absorption.

9. An electromagnetic wave absorber having a packed structure of particles having the magnetic crystal of claim 1 as a magnetic phase, and having an electromagnetic wave absorption peak in a band zone of 76 GHz±

10 GHz on a graph in which the horizontal axis indicates a frequency and the vertical axis indicates an electromagnetic wave absorption.

10. An electromagnetic wave absorber produced by binding particles having the magnetic crystal of claim 1 as a magnetic phase with a non-magnetic high-molecular compound serving as a binder, thereby forming a packed structure of the particles.

11. An electromagnetic wave absorber having a packed structure of particles having the magnetic crystal of claim 1 where M is Ga and x is from 0.1 to 0.65 as a magnetic phase, and having an electromagnetic wave absorption peak in a band zone of from 50 to 160 GHz on a graph in which the horizontal axis indicates a frequency and the vertical axis indicates an electromagnetic wave absorption.

12. An electromagnetic wave absorber having a packed structure of particles having the magnetic crystal of claim 1 where M is Al and x is from 0.2 to 0.8 as a magnetic phase, and having an electromagnetic wave absorption peak in a band zone of from 40 to 160 GHz on a graph in which the horizontal axis indicates a frequency and the vertical axis indicates an electromagnetic wave absorption.