US-12626846-B2 - Ferrite sintered magnet

US12626846B2US 12626846 B2US12626846 B2US 12626846B2US-12626846-B2

Abstract

Provided is a ferrite sintered magnet including: magnetoplumbite type ferrite crystal grains; and a two-grain boundary interposed between the ferrite crystal grains. The two-grain boundary contains Ca and La, and an atomic ratio Ca/La at the two-grain boundary is 0.3 to 3.0.

Inventors

Shirou Ootsuki
Keisuke KAMIYA

Assignees

TDK CORPORATION

Dates

Publication Date: 20260512
Application Date: 20221213
Priority Date: 20211217

Claims (4)

1 . A ferrite sintered magnet, comprising: a magnetoplumbite type ferrite crystal grains; and a two-grain boundary interposed between the ferrite crystal grains, the ferrite crystal grains contain Ca, the metal element R, Fe, and the metal element M, wherein the metal element R is selected from the group consisting of Bi and rare-earth elements, wherein the metal element M is selected from the group consisting of Zn, Cu, Mn, Al, Co, Ni, and Cr, wherein a metal composition of the ferrite sintered magnet satisfies the following Formula (5): Ca a A 2 b R c Fe d M e (5); wherein, in the Formula (5), A 2 is at least one selected from the group consisting of Sr, Ba, and Pb; a is 0.15 or more and 0.7 or less, b is 0 or more and 0.45 or less, c is 0.3 or more and 0.85 or less, d is more than 9.35 and less than 11.90, e is 0.1 or more and 0.5 or less, and the sum of a, b, and c is 1, and the two-grain boundary contains Ca and La, and a Ca/La atomic ratio at the two-grain boundary is 0.3 to 3.0.
2 . The ferrite sintered magnet according to claim 1 , wherein the Ca/La atomic ratio at the two-grain boundary is 0.4 or more.
3 . A ferrite sintered magnet, comprising: a magnetoplumbite type ferrite crystal grains; and a two-grain boundary interposed between the ferrite crystal grains, wherein the two-grain boundary contains Ca and La, and a Ca/La atomic ratio at the two-grain boundary is 0.3 to 3.0 and the two-grain boundary further contains Si, and an Si/La atomic ratio at the two-grain boundary is 0.02 to 2.0.
4 . The ferrite sintered magnet according to claim 2 , wherein the two-grain boundary further contains Si, and an Si/La atomic ratio at the two-grain boundary is 0.02 to 2.0.

Description

TECHNICAL FIELD The present disclosure relates to a ferrite sintered magnet. BACKGROUND As a magnetic material that is used in a ferrite sintered magnet, Ba ferrite, Sr ferrite, and Ca ferrite which have a hexagonal crystal structure are known (for example, refer to Patent Literatures 1 to 3). As a crystal structure of the ferrites, a magnetoplumbite type (M type), a W type, and the like are known. Among these, the magnetoplumbite type (M type) ferrite has been mainly employed as a magnet material for motors and the like. The M-type ferrite is generally represented by General Formula of AFe12O19. CITATION LIST Patent Literatures [Patent Literature 1] Japanese Unexamined Patent Publication No. 2006-206360A (Japanese Patent No. 4591684B)[Patent Literature 2] Japanese Unexamined Patent Publication No. 2005-45167A[Patent Literature 3] WO2017/200091A (Japanese Patent No. 6769482B) SUMMARY In an M-type ferrite sintered magnet, a residual magnetic flux density Br and a coercivity HcJ are likely to have a trade-off relationship. Here, in the related art, an attempt has been made to increase the residual magnetic flux density Br and the coercivity HcJ by adding an oxide of Si or Ca, or the like. However, in the M-type ferrite sintered magnet, when increasing the coercivity, the residual magnetic flux density tends to decrease significantly. The present invention has been made in consideration of such a problem, and an object thereof is to provide a novel ferrite sintered magnet capable of increasing a coercivity without significantly reducing a residual magnetic flux density. According to an aspect of the invention, there is provided a ferrite sintered magnet including: magnetoplumbite type ferrite crystal grains; and a two-grain boundary interposed between the ferrite crystal grains. The two-grain boundary contains Ca and La, and a Ca/La atomic ratio at the two-grain boundary is 0.3 to 3.0. The Ca/La atomic ratio at the two-grain boundary may be 0.4 or more. The two-grain boundary may further contain Si, and an Si/La atomic ratio at the two-grain boundary may be 0.02 to 2.0. According to the invention, there is provided a novel ferrite sintered magnet capable of increasing a coercivity without significantly reducing a residual magnetic flux density. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view of a ferrite sintered magnet. DETAILED DESCRIPTION An embodiment of the invention will be described in detail. (Ferrite Sintered Magnet) As illustrated in FIG. 1, a ferrite sintered magnet 100 according to the embodiment of the invention includes M-type ferrite crystal grains 4 having a magnetoplumbite type (M-type) crystal structure, and a grain boundary phase 6 existing between the M-type ferrite crystal grains 4. (M-Type Ferrite Crystal Grain) A crystal structure of the magnetoplumbite type pertains to a hexagonal system. A composition of the M-type ferrite crystal grains 4 is not particularly limited as long as the components thereof are oxides having the magnetoplumbite type crystal structure. The magnetoplumbite type crystal structure can be expressed by the following Formula (III). QX12O19 (III) Here, a metal element A1 and a partial metal element R enter Q (A site). Fe, a metal element M, and a metal element R as the remainder enter X (B site). Note that, in Formula (III), an atomic ratio of Q (A site) and X (B site) to O actually shows a value that slightly deviates from the above-described range, and thus the atomic ratio may slightly deviate from the above-described numerical value, for example, by approximately 10%. The M-type ferrite crystal grains 4 can contain Fe and at least one kind of metal element A1 selected from the group consisting of Ca, Sr, Ba, and Pb. In addition, the M-type ferrite crystal grains 4 can contain at least one kind of metal element R selected from the group consisting of Bi and rare-earth elements, and/or at least one kind of metal element M selected from the group consisting of zinc (Zn), copper (Cu), manganese (Mn), aluminum (Al), cobalt (Co), nickel (Ni), and chromium (Cr). The rare-earth elements are Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. For example, the composition of the M-type ferrite crystal grains may be expressed by Formula (1). A1Fe12O19 (1) A part of Fe may be substituted with the metal element M. An atomic ratio of Fe may be 50% or more. The ferrite crystal grains can be Sr ferrite in which Sr occupies 34 at % or more of A1, can be Ba ferrite in which Ba occupies 34 at % or more of A1, can be Ca ferrite in which Ca occupies 34 at % or more of A1, or may be Pb ferrite in which Pb occupies 34 at % or more of A1. In the Sr ferrite, the Ba ferrite, the Ca ferrite, and the Pb ferrite, Sr, Ba, Ca, and Pb can be the maximum components in the atomic ratio of A1, respectively. The ferrite crystal grains may contain Ca, the metal element R, Fe, and the metal element M. A metal composition of the M-type ferrite may be