A change in an optical energy profile of energy emitted from a read/write head is determined. The read/write head includes an optical transmission path that emits the energy to heat a heat-assisted recording medium during writing. A change in optical efficiency of the read/write head is also determined. Based on the change in the optical energy profile and the change in the optical efficiency, a change in the effectiveness of the read/write head is determined, and in response a mitigation is performed.

According to one embodiment, a magnetic disk device includes a disk, a head, a volatile buffer memory, a nonvolatile memory, a main power supply, and a control unit. The control unit includes a write processing unit, a management unit, a data protection processing unit, a counter, and a determination unit. When the determination unit determines that a difference has reached a threshold, the management unit returns write data of the volatile buffer memory, which is original data of write data of a track in which a count value becomes a maximum value among tracks, to a protection target.

The present disclosure generally relates to a magnetic recording system comprising a magnetic recording head that provides a low resistance cross-track current path at the trailing side of the main pole. A bias current may be driven through the path to enhance the magnetic write field to the magnetic recording media. The current is driven by an alternating current (AC) source external to the head. In some embodiments, the cross-track current going through the low resistance path enables high amounts of current to be utilized without break down of the magnetic recording head.

In accordance with an embodiment, a circuit is configured to vary an intensity of a drive current of a resistive heater element based on the digital control signal. The circuit includes and output circuit configured to control a respective slew rate and an electric energy dissipated in the resistive heater element independently of a resistance value of the resistive heater element.

A magnetic disk apparatus according to an embodiment includes a magnetic disk, a magnetic head, a second memory, and a controller. On the magnetic disk, a servo sector where first servo data is recorded is provided. The magnetic head writes data and reads data to and from the magnetic disk. The first memory stores data to be written and stores data read from the magnetic disk. The second memory stores second servo data. The controller acquires the second servo data corresponding to the first servo data from the second memory based on the first servo data read by the magnetic head when passing over the servo sector. The controller executes positioning control of the magnetic head by using the first servo data and the second servo data.

Example systems, data storage devices, and methods for using a harmonic sensor in the read channel of a data storage device to determine phase error are described. The data storage device includes a storage medium with data tracks and a head that can be positioned for reading and writing those tracks. A tone pattern may be written to a data track and a read signal from the tone pattern may subsequently be processed through the harmonic sensor to acquire amplitude data corresponding differences between a target frequency of the tone pattern and a read frequency from the read signal. The amplitude data may be processed to determine phase error values that correspond to an operating condition during writing, such as mode hops and/or down track thermal gradients related to operation of a laser during heat assisted magnetic recording.

A heat-assisted magnetic recording head includes a near-field transducer, a waveguide, and a solid immersion mirror. The near-field transducer is configured to focus and emit an optical near-field. The waveguide is configured to receive electromagnetic radiation and propagate the electromagnetic radiation toward and proximal to the near-field transducer. The solid immersion mirror is disposed proximal to the near-field transducer and along a media-facing surface of the heat-assisted magnetic recording head. The solid immersion mirror includes a first segment and a second segment disposed on opposite sides of the near-field transducer relative to a cross-track dimension of the heat-assisted magnetic recording head. The solid immersion mirror includes a thermally robust metal having a melting temperature of at least 1500 degrees Celsius. The thermally robust metal is a primary material of the solid immersion mirror.

A recording head includes a near-field transducer proximate a media-facing surface of the recording head. A light delivery waveguide extends from an energy source to the near-field transducer. The light delivery waveguide includes, proximate the near-field transducer, a C-shaped core of a first dielectric material. The C-shaped core has a hollow aligned with the near-field transducer. A cladding of a second dielectric material surrounds the C-shaped core.

According to one embodiment, a magnetic device includes a magnetic element including a first magnetic layer and a second magnetic layer, and a magnetic field generator. The magnetic field generator is configured to perform a first transition operation and a second transition operation. In the first transition operation, a first state where a first magnetic field is generated is configured to transit to a second state where a second magnetic field is generated. In the second transition operation, the second state is configured to transit to the first state. The first magnetic field includes a first component in a first orientation from the first magnetic layer to the second magnetic layer. The second magnetic field includes a second component in a second orientation from the second magnetic layer to the first magnetic layer.

Described are magnetic recording heads that include auxiliary current wires that drive the write pole tip, augmenting the main coils that provide magnetomotive force to the write pole. The auxiliary wires are provided in close proximity to the write pole tip near the media-facing surface of the recording head, and are preferably in closer proximity to the write pole tip than are the main coils. In certain writer designs that include one or more heat sink structures positioned near or around the write pole tip, such as may be found in heat-assisted magnetic recording writer constructions, the auxiliary wire(s) may be accommodated near or around the heat sink structures, or the heat sink structures themselves can serve as the auxiliary wires.