Magnetic disk device

1. A magnetic disk device comprising:

a magnetic disk;

a magnetic head configured to write data on the magnetic disk;

an assist section configured to assist, when the magnetic head writes data on the magnetic disk, write of the data by utilizing an assist element;

a voltage control section configured to control a voltage to be applied to the assist element;

a positioning control section configured to carry out positioning of the magnetic head relatively to the magnetic disk on the basis of servo data and acquire positional error data of the magnetic head positioned on the basis of the servo data; and

a voltage adjustment control section configured to adjust the magnitude of the voltage to be applied to the assist element by the voltage control section when the positional error data exceeds a predetermined value, wherein

the voltage adjustment control section adjusts the magnitude of the voltage of the voltage control section on the basis of the positional error data in such a manner as to make the voltage to be applied to the assist element smaller as the positional error becomes greater, and

an amount by which the voltage to be applied to the assist element is made smaller is determined on the basis of a tendency of an average element lifetime relative to the voltage to be applied to the assist element.

2. The magnetic disk device of claim 1 , wherein

the assist element is a spin-torque oscillator element configured to oscillate high-frequency waves, and

the assist section is a high-frequency assist section configured to assist write of data by using the spin-torque oscillator element.

3. The magnetic disk device of claim 1 , wherein

the assist element is an optical element configured to emit laser light, and

the assist section is a thermal assist section configured to assist write of data by using the optical element.

4. A magnetic disk device of claim 2 , wherein comprising:

a magnetic disk;

a magnetic head configured to write data on the magnetic disk;

an assist section configured to assist, when the magnetic head writes data on the magnetic disk, write of the data by utilizing an assist element;

a voltage control section configured to control a voltage to be applied to the assist element;

a positioning control section configured to carry out positioning of the magnetic head relatively to the magnetic disk on the basis of servo data and acquire positional error data of the magnetic head positioned on the basis of the servo data; and

a voltage adjustment control section configured to adjust the magnitude of the voltage to be applied to the assist element by the voltage control section when the positional error data exceeds a predetermined value, wherein

when the voltage to be applied to the assist element of the magnetic head in which the variance value of the positional error data is the smallest is set as a first voltage, and the voltage to be applied to the assist element of the magnetic head in which the variance value of the positional error data is the largest is set as a second voltage,

the voltage adjustment control section adjusts the magnitude of the voltage to be applied to the assist element by the voltage control section in such a manner that the first voltage becomes greater than or equal to the second voltage.

5. The magnetic disk device of claim 4 , wherein

the assist element is a spin-torque oscillator element configured to oscillate high-frequency waves, and

the assist section is a high-frequency assist section configured to assist write of data by using the spin-torque oscillator element.

6. The magnetic disk device of claim 4 , wherein

the assist element is an optical element configured to emit laser light, and

the assist section is a thermal assist section configured to assist write of data by using the optical element.

7. A magnetic disk device comprising:

a magnetic disk;

a magnetic head configured to write data on the magnetic disk;

an assist section configured to assist, when the magnetic head writes data on the magnetic disk, write of the data by utilizing an assist element;

a voltage control section configured to control a voltage to be applied to the assist element;

a positioning control section configured to carry out positioning of the magnetic head relatively to the magnetic disk on the basis of servo data and acquire positional error data of the magnetic head positioned on the basis of the servo data; and

a voltage adjustment control section configured to adjust the magnitude of the voltage to be applied to the assist element by the voltage control section when the positional error data exceeds a predetermined value,

which further comprising three or more sets of the magnetic disk and the magnetic head, wherein

the three or more sets are accommodated in a housing including a top cover and a base, and

when an average value of the voltage to be applied to the assist element of the magnetic head closest to the top cover side and the voltage to be applied to the assist element of the magnetic head closest to the base side is set as a third voltage, and an average value of the voltages to be applied to the assist elements of the magnetic heads other than the magnetic heads closest to the top cover side and the base side is set as a fourth voltage,

the voltage adjustment control section adjusts the magnitude of the voltage to be applied to each of the assist elements by the voltage control section in such a manner that the fourth voltage becomes greater than or equal to the third voltage.

8. The magnetic disk device of claim 7 , wherein

the assist element is a spin-torque oscillator element configured to oscillate high-frequency waves, and

the assist section is a high-frequency assist section configured to assist write of data by using the spin-torque oscillator element.

9. The magnetic disk device of claim 7 , wherein

the assist element is an optical element configured to emit laser light, and

the assist section is a thermal assist section configured to assist write of data by using the optical element.