WO2001059768A2

WO2001059768A2 - High data rate writer poles

Info

Publication number: WO2001059768A2
Application number: PCT/US2000/027510
Authority: WO
Inventors: Shuwei Sun; Ned Tabat
Original assignee: Seagate Technology Llc
Priority date: 1999-10-05
Filing date: 2000-10-05
Publication date: 2001-08-16
Also published as: WO2001059768A3

Abstract

A magnetic head including a first writer pole (100) disposed on a second writer pole (102). The second pole forms a magnetic path with the first pole and first pole includes a film with a chemical formula of (Fe60Co40)100-xMx. M can be one or more elements selected from the list of Hf, Zr, Ta, Nb, Cu, C, V, and Pd. The variable x can be in the range of approximately 9 to 14 atomic percent. The film can be of a thickness in the range of approximately 1 micron to 2 micron. The first pole and the second pole can be connected at one end. The film can include a sputtered thin film. The second pole can include the same film as the first pole. The film can include a very fine grain nanostructure phase. In another aspect of this invention, a method for forming a magnetic head is disclosed. The method includes depositing a first writer pole, and depositing a second writer pole adjacent to the first pole. The second pole forms a magnetic path with the first pole. The first pole includes a film as specified above. The first pole can be deposited at a pressure of approximately 5-25 mT.

Description

HIGH DATA RATE WRITER POLES

BACKGROUND

Thin film magnetic recording heads are used in the data storage industry for recording data onto narrow tracks on a magnetic medium. In a hard disc drive, a thin film head may be mounted to a head-gimbal-assembly, which is used to position the head over concentric data tracks on a disk surface. Thin film heads may also be used with other magnetic medium types.

A thin film head typically includes a writer and a reader. The writer includes two magnetic layers, called writer poles or magnetic poles, separated by an insulating layer. The poles are typically conductively connected at one end and are separated by a thin insulating layer at the other end. Such a configuration can result in a somewhat horseshoe-like shape. Conductive wires are embedded within the insulating layer between the poles to form a coil that is used to create a magnetic field and write data to the magnetic medium.

During a write operation, a magnetic flux is induced in the poles by an electrical current flowing through the coil. This magnetic flux flows through the connected writer pole layers, but is impeded by their separation at the front gap. The pole separation at the front gap results in a discontinuity causing a magnetic field to protrude onto regions near the gap. This protruding field can be used to record data onto a magnetic medium. In a digital storage device, changes in magnetic flux orientation caused by changes in the direction of current flow in the coil are used to write data to the magnetic medium. For example, a positive magnetic flux may be generated from a current flowing through the coil in a first direction, while a negative magnetic flux may be generated by changing the direction of the current. The positive and negative magnetic fluxes can be used to stored "1" and "0" bit values on the magnetic medium by varying the bias of magnetic dipoles in the medium. For example, a positive dipole bias may represent a "1 " bit value while a negative bias may represent a "0" bit value.

Magnetic properties of the thin film materials used in magnetic poles can deteriorate at high frequencies. Recording data rates and frequencies have increased as recording areal density and rotational speed have increased to improve the performance and storage capacity of the hard disc drive. In current hard disc drives, the data rate for a 20 Gb/in² design is approximately 517 Mb/sec with a frequency of 258 MHz. For other high performance hard disc drives, the data rate is approximately 700Mb/sec with a frequency of 350MHz. Current writer pole materials, such as permalloy, Ni ₅Fe₅₅, and CoNiFe, are typically limited to a frequency lower than 300 MHz. Thus, high density and high data rate recording heads require the development of high frequency magnetic materials for the writer poles.

SUMMARY Accordingly, the present invention relates to a thin film material used in writer poles.

This invention discloses a magnetic head including a first writer pole disposed on a second writer pole. The second pole forms a magnetic path with the first pole and the first pole includes a film with the chemical formula of (Fe₆oCo ₀)₁₀o-_xM_x. M can be one or more elements selected from the list of Hf, Zr, Ta, Nb, Cu, C, Y, and Pd. The variable x can be in the range of approximately 9 to 14 atomic percent. The film can be of a thickness in the range of approximately 1 micron to 2 micron. The first pole can be a top pole and the second pole can be a bottom pole. The first pole and the second pole can be connected at one end. The film can include a sputtered thin film. The second pole can include the same film as the first pole. The film can include a very fine grain nanostructure phase. In another aspect of this invention, the magnetic head includes a first writer pole disposed on a second writer pole. The second pole forms a magnetic path with the first pole. The first pole includes a film with the chemical formula of (Fe₆₀Co₄o)₁oo-_xHf_x and the variable x is in the range of approximately 9 to 14 atomic percent.

In another aspect of this invention, the magnetic head includes a first writer pole disposed on a second writer pole. The second pole forms a magnetic path with the first pole. The first pole includes a film with the chemical formula of (Fe₆oCo o)₁₀₀._xZr_x and the variable x is in the range of approximately 9 to 14 atomic percent.

In another aspect of this invention, a method for forming a magnetic head is disclosed. The method includes depositing a first writer pole, and depositing a second writer pole adjacent to the first pole. The second pole forms a magnetic path with the first pole. The first pole includes a film with a chemical formula of (Fe₆oCo₄₀)₁oo-_xM_x. M can be one or more elements selected from the list of Hf, Zr, Ta, Nb, Cu, C, N, and Pd. The variable x is in the range of approximately 9 to 14 atomic percent. The film can have a thickness in the range of approximately 1 micron to 2 micron. The film can include a sputtered thin film. The second pole can be made of the same film as the first pole. The film can include a very fine grain nanostructure phase. The film can be deposited at a pressure of approximately 5 to 25 mT and a power of approximately 500 to 3000W. The details of the methodology can be found in the Detailed Description section below. The advantages of this invention may include the following:

The new thin film materials can have a very high resistivity, moderately high saturation induction, soft magnetic properties, excellent corrosion resistance, and good thermal stability. Its initial permeability can be constant with a frequency over a bandwidth three times that of the prior art materials. Furthermore, the new thin film materials can be used in high data rate writes without the need for lamination.

The new thin film materials can have a very fine grain nanostructure phase. These structures may be responsible for the very high resistivity and the soft magnetic properties.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section of a hard disc writer.

FIG. 2 is a data table comparing different writer pole materials.

FIG. 3 is a graph of the roll-off frequency of the hard axis initial permeability of FeCoHf. FIG. 4 is a graph of the FeCoHf hard axis initial permeability controlled by the magnetic current of the electromagnetic field in the substrate.

FIG. 5 is a graph of the FeCoHf material stress and deposition pressure.

FIG. 6 is a data table comparing FeCoHf with known writer pole materials.

FIG. 7a and b are graphs indicating the very fine grain nanostructure phase of FeCoHf.

FIG. 8 is a graph of the resistivity of FeCoHf.

FIG. 9 is a graph of the Bs and He of FeCoHf after 40 hours of cross magnetic annealing.

DETAILED DESCRIPTION

The present invention relates to a thin film material used in writer poles of a hard disc drive head. Referring first to FIG. 1, a thin film head is presented. The reader portion of the head includes a reader sensor 106, a top shield 105, and a bottom shield 107 separated by a reader gap 109. The writer portion of the head includes two magnetic poles, a top pole 100 and a bottom pole 102 typically deposited on a non-magnetic substrate 104. The bottom pole 102 forms a magnetic path with the top pole 100. The writer poles are typically conductively connected at one end and are separated by a thin insulating layer 108 on the other end. A writer coil 101 is embedded within the insulating layer 103 between the top pole 100 and the bottom pole 102 to form a coil 101 that is used to write the data to the magnetic medium.

The writer poles 100 and 102 typically consist of a thin film material. High frequency magnetic performance is dependent on the film resistivity of the thin film material. Film resistivity is the ratio of the electric field to the current density, such that the smaller the resistivity, the better the conductor. Increasing resistivity in a writer pole 100 or 102 can reduce eddy current. Eddy current is the induced current flow in the writer poles 100 and 102. The increased resistivity in the writer poles can result in increasing the writer poles working frequency, while maintaining good magnetic properties, corrosion resistance, and thermal stability suitable for writer head use at high frequencies.

In general, magnetic materials have two kinds of energy loss at high frequencies: hysteresis loss due to damping in the magnetizing process and Ohmic loss due to eddy current. At even higher frequencies there can also be various resonance and energy absorption, which result in energy loss. These energy losses can cause permeability (μ) as a function of frequency. Permeability is the ratio of magnetic induction (B) to the magnetic field (H) and can be split into a real and imaginary part (μ=μ'-μ"). The higher the permeability, the easier it becomes to conduct magnetic flux.

These energy losses also cause skin effect in the electromagnetic field penetration depth. As the electromagnetic field penetrates into conductive materials, the field strength reduces with the depth from the surface. When the electromagnetic strength reduces to 1/e, the depth is known as skin depth. The skin depth gets shallower with increasing frequency. When the skin depth is equal to the film thickness, the μ' rolloff will occur. From electrodynamics analysis, the maximum rolloff frequency is:

max = ^' ζ Equation 1

where p is the film resistivity, t is the film thickness, μ_s is the static permeability, and c is the speed of light.

Therefore, to get to higher working frequencies magnetic materials with high resistivity or thinner films should be chosen. High resistivity can be generated with films having a fine grain nanostructure or an amorphous phase, which can be accomplished, for example, by adding certain refractory elements or metalloid elements to the magnetic materials. Examples of refractory elements include Hf and Ta, and examples of metalloid elements include B, C, and Si. In an embodiment of this invention, the materials selected for the thin film of the writer pole include (Fe₆₀Co₄o)₁₀o._xM_x, wherein M is an element or a combination of the elements Hf, Zr, Ta, Nb, Cu, C, N, and Pd, and x is in the range of approximately 9 to 14 atomic percent. By choosing thin films that increase resistivity, the upper frequency limit of these films can be increased because of the reduction of the eddy current. Meanwhile, these films can also maintain high saturation magnetic induction, small coercivity, good corrosion resistance, and good thermal stability as required by writer pole design. This is shown in FIG. 2, which shows a comparison of the selected films with known films used in writer pole applications. The table lists the resistivity (p), saturation magnetic induction (Bs), coercivity (He), initial permeability along the hard axis (IP-h), and magnetic anisotroty field (Hk). The Bs is the magnetic flux density. The initial permeability along the hard axis is measured when the electromagnetic field is close to zero. As FIG. 2 demonstrates, the selected thin films have a high resistivity, while maintaining features useful for a thin film material for use in writer poles. The selected thin film materials can be in the range of approximately 0.1 μm to 2 μm thick while maintaining their properties. The writer pole material can be deposited on the substrate by a DC magnetron, RF diode sputtering, electroplating, or by methods known and used by those persons skilled in the art.

As can be seen by FIG. 2, (Fe₆₀Co₄o)₁oo-χHf_x ("FeCoHf) films are particularly effective. This is because FeCoHf films have a high resistivity of approximately 130-150 μΩ.cm. The resistivity of FeCoHf films are almost three times that of Νi₄₅Fe₅₅, a prior art thin film material used in writer poles. The working frequency of the FeCoHf films, therefore, can be three times that of Ni ₅Fe₅₅. The FeCoHf films can have a moderately high saturation induction of 16-17 kG, which is similar to Ni₄₅Fe₅₅. The saturation induction does not change when the film thickness increases between approximately 0.1 μm and 2 μm. The selected thin films can be magnetically soft. For example, the coercivity of the

FeCoHf films is approximately 2 Oe for films 0.1 μm thick. The selected films can get even softer as they get thicker. For example, the coercivity is approximately 0.8 Oe for films 2 μm thick, which is comparable with Ni₄₅Fe₅₅, a prior art thin film for writer poles. The selected thin films can also have excellent corrosion resistance. For example, the corrosion current of the FeCoHf films can be less than 0.05 (μA/cm²) in a KC1 solution with pH = 5.8. This result is an order of magnitude lower than the corrosion current of FeCo, a prior art thin film for writer poles. The selected films can also has passive potential, which indicates that they can have less corrosion risk when in contact with other metals.

The selected films can have very smooth surface morphology. The surface roughness of the FeCoHf films is only approximately 4 A measured by AFM, which is about one eighth of the surface roughness of FeCo. The selected films also have a very fine grain nanostructure phase. As is shown in FIGS. 3 and 4, the thin films can have an initial permeability that is constant with a frequency over a bandwidth three times that of Ni₄₅Fe₅₅. The writer pole, therefore, can be used for high data rate writes without the need for lamination.

FIG. 3 is a graph of the actual maximum rolloff frequency for FeCoHf as 3 GHz, which is similar to the predicted maximum rolloff frequency of Equation 1. FIG. 4 is a graph of the hard axis initial permeability. As is shown by the graph, varying the magnetic current in an electromagnet underneath the substrate can control the hard axis initial permeability.

FIG. 5 is a graph of the material stress and deposition pressure of FeCoHf. As stress increases, the magnetic domain structure worsens. Therefore, zero stress is preferred. As FIG. 5 shows, varying the deposition pressure can control stress. At a deposition pressure of approximately 5-25 mT, the stress will be close to zero.

FIG. 6 shows FeCoHf compared to other known thin film materials. The data in the table indicates that FeCoHf films are good materials for high data rate and high density writer poles. The resistivity (p) of FeCoHf can be almost three times that of most of the other writer pole materials. The saturation magnetic induction (Bs) and coercivity (He) can be comparable to other writer pole materials. The roll-off frequency can be more than three times that of other writer pole materials. And the initial permeability along the hard axis is improved over the other writer materials.

FIG. 7a is an XRD graph of FeCoHf and FIG. 7b is a TEM graph of FeCoHf. FIGS. 7a and b show that FeCoHf has a very fine grain nanostructure phase, which can increase the resistivity for use in thin films for writer poles.

FIG. 8 is a graph that shows the resistivity for FeCoHf, which is approximately 130- 150 μΩ.cm. It also shows that the coercivity of FeCoHf decreases to lower than lOe when the Hf concentration is in the range of 9-14 atomic percent. FIG. 9 is a graph that shows the saturation magnetic induction (Bs) and coercivity (He) of FeCoHf compared to its cross magnetic annealing time. As the graph demonstrates, the saturation magnetic induction and coercivity remain relatively constant through 40 hours. The selected films that are thicker than 0.5 μm can have good thermal stability against disturbance from elevated temperature and perpendicular magnetic fields. For example, the FeCoHf films cross magnetic anneal conditions are: 100°C, 40 hours, in a 250 Oe magnetic field perpendicular to the easy axis. The resistivity, saturation induction, and coercivity do not show apparent changes after the cross magnetic anneal. The easy axes of the films thicker than 0.5 μm were unchanged from their original direction. As can also be seen in FIG. 2, (FeeoCo^oo-xZrx films are also particularly effective.

The variable x is in the range of approximately 9 to 14 atomic percent. Using Zr films can result in a high resistivity of about 10 μΩ.cm, with a lower saturation induction of about 1 kG, which can be suitable for writer pole use in high data rate and high density recording heads. These thin films, and other materials with similar properties such as those listed above, are therefore suitable for writer pole materials, including the first and second magnetic poles, in high data rate and high density recording heads.

Claims

WHAT IS CLAIMED IS:

1. A magnetic head comprising: a first writer pole disposed on a second writer pole, wherein the second pole forms a magnetic path with the first pole; wherein the first pole comprises a film comprising:

(Fe₆₀Co₄o)₁₀o._xM_x .

2. The magnetic head of claim 1 wherein M is one or more elements selected from the list consisting of Hf, Zr, Ta, Nb, Cu, C, V, and Pd.

3. The magnetic head of claim 1 wherein the variable x is in the range of approximately 9 to 14 atomic percent.

4. The magnetic head of claim 1 , wherein the film further comprises a thickness in the range of approximately 1 micron to 2 micron.

5. The magnetic head of claim 1, wherein the first pole comprises a top pole and the second pole comprises a bottom pole.

6. The magnetic head of claim 1, wherein the first pole and the second pole are connected at one end.

7. The magnetic head of claim 1, wherein the film further comprises a low coercivity and a high saturation magnetic induction.

8. The magnetic head of claim 1, wherein the second pole comprises the same film as the first pole.

9. The magnetic head of claim 1 , wherein the film further comprises a very fine grain nanostructure phase.

10. A magnetic head comprising: a first writer pole disposed on a second writer pole, wherein the second pole forms a magnetic path with the first pole; wherein the first pole comprises a film comprising:

(Fe₆₀Co₄o)₁₀₀-_xHf_x ; and the variable x is in the range of approximately 9 to 14 atomic percent.

11. A magnetic head comprising: a first writer pole disposed on a second writer pole, wherein the second pole forms a magnetic path with the first pole; wherein the first pole comprises a film comprising:

(Fe₆₀Co₄₀)₁oo._xZr_x ; and the variable x is in the range of approximately 9 to 14 atomic percent.

12. A method for forming a magnetic head comprising: depositing a first writer pole; and depositing a second writer pole adjacent to the first writer pole, wherein the second pole forms a magnetic path with the first pole; wherein the first pole comprises a film comprising:

(Fe₆₀Co₄o)₁₀o-_xM_x •

13. The method of claim 12 wherein M is one or more elements selected from the list consisting of Hf, Zr, Ta, Nb, Cu, C, V, and Pd.

14. The method of claim 12 wherein the variable x is in the range of approximately 9 to 14 atomic percent.

15. The method of claim 12, wherein the film further comprises a thickness in the range of approximately 1 micron to 2 micron.

16. The method of claiml2, wherein the film further comprises a low coercivity and a high saturation magnetic induction.

17. The method of claim 12, wherein the film further comprises a sputtered thin film.

18. The method of claim 12, wherein the film further comprises a very fine grain nanostructure phase.

19. The method of claim 12, wherein the first pole is deposited at a pressure of approximately 5-25 mT.

20. A magnetic head comprising: a first writer pole deposited on a second writer pole, wherein the second pole forms a magnetic path with the first pole; and magnetic pole thin film means for increasing the resistivity of the first pole for operating the magnetic head at high frequencies.