According to one embodiment, a magnetic disk device applies a bias voltage for measurement to a high frequency assist element according to a setting instruction of the bias voltage to measure a conduction current by in a recording head, calculates the resistance value in the supply path of the bias voltage from a relationship between the measured current and the bias voltage for measurement, and changes the bias voltage applied at the time of data recording based on the calculated resistance value.

According to one embodiment, a magnetic disk device applies a bias voltage for measurement to a high frequency assist element according to a setting instruction of the bias voltage to measure a conduction current by in a recording head, calculates the resistance value in the supply path of the bias voltage from a relationship between the measured current and the bias voltage for measurement, and changes the bias voltage applied at the time of data recording based on the calculated resistance value.

A PMR writer is disclosed wherein a top yoke (TY) is extended toward the air bearing surface (ABS) and below a top coil for faster saturation speed and better frequency extendibility without wide adjacent track erasure trade-off. The TY extension has a front side recessed 0.9-1.3 microns from the ABS, and has a backside below an inner corner of a PP3 trailing shield that is 2-2.6 microns from the ABS. TY thickness is from 0.3-0.8 micron and the TY is preferably used with a 1+1T coil design, and a PP3 trailing shield apex angle of 60 to 80 for better high data rate performance. Magnetic modeling shows rise time is shorter than for a conventional TY. The top yoke design is compatible with various base writer structures. When used in selectable double writers or selectable triple writers, each writer has a separate TY, main pole, and bottom yoke.

A spin transfer torque (STT) device has a free ferromagnetic layer that includes a Heusler alloy layer and a template layer beneath and in contact with the Heusler alloy layer. The template layer may be a ferromagnetic alloy comprising one or more of Co, Ni and Fe and the element X, where X is selected from one or, more of Ta, B, Hf, Zr, W, Nb and Mo. A CoFe nanolayer may be formed below and in contact with the template layer. The STT device may be a spin-torque oscillator (STO), like a STO incorporated into the write head of a magnetic recording disk drive. The STT device may also be a STT in-plane or perpendicular magnetic tunnel junction (MTJ) cell for magnetic random access memory (MRAM). The template layer reduces the critical current density of the STT device.

A spin transfer torque (STT) device has a free ferromagnetic layer that includes a Heusler alloy layer and a template layer beneath and in contact with the Heusler alloy layer. The template layer may be a ferromagnetic alloy comprising one or more of Co, Ni and Fe and the element X, where X is selected from one or, more of Ta, B, Hf, Zr, W, Nb and Mo. A CoFe nanolayer may be formed below and in contact with the template layer. The STT device may be a spin-torque oscillator (STO), like a STO incorporated into the write head of a magnetic recording disk drive. The STT device may also be a STT in-plane or perpendicular magnetic tunnel junction (MTJ) cell for magnetic random access memory (MRAM). The template layer reduces the critical current density of the STT device.

A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a spin torque oscillator (STO) element. The data storage device further comprises a differential amplifier comprising a first input coupled to a first end of the STO element and a second input coupled to a second end of the STO element. A bias current is applied to the STO element, and the bias current is adjusted. A resistance delta of the STO element is detected based on an output of the differential amplifier, wherein the resistance delta corresponds to a bias current level when the STO begins to oscillate.

A dual perpendicular magnetic recording writer is disclosed wherein the better of two writers on a slider is determined by performance testing, and is then integrated into a head gimbal assembly. Main pole layers in the two writers are separated by a cross-track width <10 microns to minimize read-write offset. Each of the driving coil (DC) and bucking coil (BC) have two outer portions forming a U shape with a front side, and each have a center portion connected to the front side proximate to an air bearing surface and a backend contacting an interconnect. A write current passes from a BC outer portion below the main pole in the selected writer through the BC center portion to the interconnect, and then through the DC center portion to a DC outer portion above the main pole in the selected writer. Area density capability mean and sigma are improved.

A dual perpendicular magnetic recording writer is disclosed wherein the better of two writers on a slider is determined by performance testing, and is then integrated into a head gimbal assembly. Main pole layers in the two writers are separated by a cross-track width <10 microns to minimize read-write offset. Each of the driving coil (DC) and bucking coil (BC) have two outer portions forming a U shape with a front side, and each have a center portion connected to the front side proximate to an air bearing surface and a backend contacting an interconnect. A write current passes from a BC outer portion below the main pole in the selected writer through the BC center portion to the interconnect, and then through the DC center portion to a DC outer portion above the main pole in the selected writer. Area density capability mean and sigma are improved.

Dual and triple PMR writers are disclosed wherein the number of writer pads required to energize the selected PMR writer is minimized to three or four, respectively, with a coil configuration wherein separate top coils are connected by separate interconnects or side taps to separate bottom coils. Either top coils or bottom coils may be linked to a common W pad. Alternatively, there may be one bottom coil that allows all output current to flow to a common W pad. Coils may have a pancake or helical shape. In dual PMR writer embodiments, there may be one or two dynamic fly height heater coils. Magnetic performance in the selected writer of a dual PMR writer is similar to that of a single PMR writer with regard to erase width in AC mode (EWAC), Hy field, trailing and side shield return fields, down-track and cross-track gradient.

Dual and triple PMR writers are disclosed wherein the number of writer pads required to energize the selected PMR writer is minimized to three or four, respectively, with a coil configuration wherein separate top coils are connected by separate interconnects or side taps to separate bottom coils. Either top coils or bottom coils may be linked to a common W pad. Alternatively, there may be one bottom coil that allows all output current to flow to a common W pad. Coils may have a pancake or helical shape. In dual PMR writer embodiments, there may be one or two dynamic fly height heater coils. Magnetic performance in the selected writer of a dual PMR writer is similar to that of a single PMR writer with regard to erase width in AC mode (EWAC), Hy field, trailing and side shield return fields, down-track and cross-track gradient.