Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-07-06
2001-02-13
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S900000, C360S112000, C324S252000, C250S492200
Reexamination Certificate
active
06187458
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a ferromagnetic fine line and magnetic apparatus ideal for utilization in a wide range of applications such as high density magnetic recording and magnetic sensors by controlling magnetization by means of the proximity of the electrodes and the structure on an atomic level, and by preserving the magnetization characteristics by embedding on a nonmagnetic atomic layer.
Material with ferromagnetic characteristics has the property of spontaneous magnetization, in other words, the characteristic of generating a finite amount of magnetism without application of power to the magnetic material. The finite magnetization of the ferromagnetic material; might not be indicated by the bulk quantity of magnetic material however, a piece of ferromagnetic material can be internally divided into a plurality of regions. Each of these regions shows a finite amount of magnetism; however, the direction of the magnetism differs with each respective region. These regions, in other words, each small zone where the magnetism has a fixed direction, is referred to as a magnetic domain.
Material having ferromagnetic properties is utilized in many ways in a wide variety of applications, such as all kinds of magnetic recording and magnetic sensors. Development of material with ferromagnetic properties suited for different objectives is currently proceeding at a vigorous pace. In the area of magnetic recording in particular, to meet demands for ever greater high density recording, a crucial issue is how to make these magnetic domains as small as possible in as few magnetic domains as possible and yet still perform magnetic recording.
Practical magnetic recording is currently still at the stage of having to use a plurality of magnetic domains per unit of magnetic recording. Preferably, a single magnetic domain should function as a magnetic recording unit and the size of this magnetic domain should preferably be as small as possible. A method utilizing electron beam lithography, for instance, to make small magnetic domains in ferromagnetic material has been proposed in the Journal of Applied Physics, Vol. 76, pp. 6673-6675 (1994). In this method, regions of several dozen nanometers consisting of magnetic atoms were formed on a nonmagnetic substrate, in other words a substrate showing no ferromagnetic properties, and a ferromagnetic pillar array consisting of a single magnetic domain were also reported. Atoms discovered with ferromagnetic properties here having a single bulk quantity were the 3d transition metals Cr, Mn, Fe, Co, Ni as well as the lanthanides Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu. A method proposed in the Journal of Applied Physics, Vol. 76, pp. 6656-6660 (1994), for instance, showed that ferromagnetic particle arrays of approximately the same size can be formed by depositing the ferromagnetic material on a nonmagnetic substrate utilizing the probe of a scanning tunneling microscope (STM).
However, merely applying these two methods as is in order to achieve a still further reduction in the size of the magnetic portion will not work well. The reason can be explained with the Stoner model which is often used to describe typical ferromagnetic material such as Fe, Co, and Ni. This Stoner model, as related in the Tokyo University Bussei Kenkyu-jo, “Bussei Kagaku Jiten”, pp. 198-200, Tokyo Shoseki (1996), expresses conditions (Stoner conditions) for discovering ferromagnetism by U×D(EF)>1 where U is the electron correlation energy or energy of coulomb repulsion between electrons and D (Ef) is the electron state density at the Fermi level EF. Therefore, a material must have an extremely large state density D (EF) at the Fermi level in order to exhibit ferromagnetic properties. However, when the bulk ferromagnetic piece for satisfying the above mentioned Stoner conditions is comprised of atomic cluster types of a minute size or elongated atomic types, then the state density D (EF) decreases drastically due to the finite size effect. Consequently, the Stoner condition has not been met and there is a high probability that the spontaneous magnetism has been lost. Accordingly, a new method completely different from those of the conventional art is required in order to achieve a ferromagnetic fine line with even smaller magnetic domains.
SUMMARY OF THE INVENTION
In view of the above problems it is therefore an object of the present invention to provide a ferromagnetic fine line and a magnetic apparatus thereof characterized by being able to control the magnetization by means of the proximity of the electrodes and the structure on an atomic level, and able to protect the magnetization characteristic from the adherence of impurities by means of embedding in an atomic layer, with no loss of spontaneous magnetization when the magnetic domains are even smaller than the conventional art.
In order to resolve the above mentioned problems, this invention utilizes the fact that the array of the atomic cluster (including molecules) of the solid surface and atoms on the solid surface, differs from the electron state of a bulk (solid); in other words, a lump or cluster that is macroscopic in size. Restated, ferromagnetic properties can be discovered by the appropriate array or ordering of atoms on the surface of a substrate. Further, embedding within a protective atom layer ensures that no loss of magnetization characteristics will occur on the surface of the solid with this atomic array, and weakening of magnetization characteristics is prevented by absorption of impurities. One other special feature deserving note in this atomic level array, is that ferromagnetic characteristics can be displayed just by using non-magnetic atoms. Here nonmagnetic atoms indicates atoms without magnetic properties, excluding atoms previously defined as magnetic or rare gas molecules (He, Ne, Ar, Kr, Xe, Rn). In this atomic level array, ferromagnetism can be expressed with nonmagnetic atoms and magnetic atoms, or just with magnetic atoms.
As related previously, conditions (Stoner condition) for displaying ferromagnetism are expressed by U×D(Ef)>1 where U is the electron correlation energy or energy of coulomb repulsion between electrons, D (Ef) is the electron state density at the Fermi level. Therefore, even in a bulk (solid) of substance groups with nonmagnetic characteristics, ferromagnetism can be obtained if the Stoner condition of U×D(Ef)>1 can be satisfied by the proper array of atoms on the surface of the substrate. The appearance for instance, of spontaneous magnetism at the end of ribbon-shaped graphite can theoretically be predicted as mentioned in the Journal of the Physical Society of Japan, Vol. 65, pp. 1920-1923 (1996). However such a structure is only theoretical and has not actually been achieved.
In this invention, ultra-fine fabricating technology is utilized on the atomic level by utilizing methods such as STM to form an atomic level array or order on the surface of a nonmagnetic substrate. At this time, the detailed configuration of the state density of the atomic level array will vary according to the atomic type and array, and this invention is characterized in that the peak of the state density occurs in the vicinity of the Fermi level. The peak of this state density permits the Stoner condition to be satisfied and ferromagnetism to be achieved.
REFERENCES:
patent: 5561300 (1996-10-01), Wada et al.
patent: 5968677 (1999-10-01), Watanabe
“Peculiar Localized State at Zigzag Graphite Edge”, M. Fujita et al, Journal of Physical Society of Japan, vol. 65, 1996, pp. 1920-1923.
“Interaction of Ga Adsorbates with Dangling Bonds on the Hydrogen Terminated Si(100) Surface”, by T. Hashizume et al, Japanese Journal of Applied Physics, vol. 65, 1996, pp. 1085-1088.
“Single-domain magnetic pillar array of 35nm diameter and 65Gbits/in2 density for ultrahigh density quantum magnetic storage”, by S. Y. Chou et al; Journal of Applied Physics, vol. 76, 1994, pp. 6673-6675.
“Properties and measurement of scanning tunneling microscope f
Hashizume Tomihiro
Ichimura Masahiko
Ono Yoshimasa
Onogi Toshiyuki
Wada Yasuo
Hitachi , Ltd.
Kiliman Leszek
Mattingly Stanger & Malur, P.C.
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