An apparatus comprises a slider having an air bearing surface (ABS) and a near-field transducer (NFT) at or near the ABS. An optical waveguide is configured to couple light from a laser source to the NFT. A resistive sensor comprises an ABS section situated at or proximate the ABS and a distal section extending away from the ABS to a location at least lateral of or behind the NFT. The resistive sensor is configured to detect changes in output optical power of the laser source and contact between the slider and a magnetic recording medium.

A data storage device is disclosed comprising a disk, a head for accessing the disk, and a sensor for generating an alternating sensor signal. The sensor is disconnected from an input of a sensing circuit and while the sensor is disconnected an alternating calibration signal is injected into the input of the sensing circuit, wherein the alternating calibration signal comprises a predetermined offset and amplitude. A response of the sensing circuit to the alternating calibration signal is evaluated to detect at least one of an offset and a gain of the sensing circuit.

A magnetic head for perpendicular magnetic recording includes a read head unit, a write head unit disposed forward of the read head unit along the direction of travel of a recording medium, a heater that generates heat for causing the medium facing surface to protrude in part, an expansion layer that makes part of the medium facing surface protrude, and a sensor that detects contact of the part of the medium facing surface with the recording medium. The write head unit includes a main pole, a write shield, and a return path section. The return path section includes a yoke layer located backward of the main pole along the direction of travel of the recording medium, a first coupling part that couples the yoke layer and the write shield to each other, and a second coupling part that is located away from the medium facing surface and couples the yoke layer and the main pole to each other.

A sensor supported by a head transducer has a temperature coefficient of resistance (TCR) and a sensor resistance. The sensor operates at a temperature above ambient and is responsive to changes in sensor-medium spacing. Conductive contacts connected to the sensor have a contact resistance and a cross-sectional area adjacent to the sensor larger than that of the sensor, such that the contact resistance is small relative to the sensor resistance and negligibly contributes to a signal generated by the sensor. A multiplicity of head transducers each support a TCR sensor and a power source can supply bias power to each sensor of each head to maintain each sensor at a fixed temperature above an ambient temperature in the presence of heat transfer changes impacting the sensors. A TCR sensor of a head transducer can include a track-oriented TCR sensor wire for sensing one or both of asperities of the medium.

A data storage device may have increased signal-to-noise ratio contact detection by employing a transducing head associated with a data storage medium each connected to a controller. The transducing head can have an alternating current heater excited to a first frequency for a first revolution of the data storage medium and to a different second frequency for a second revolution of the data storage medium. The second frequency may produce lateral transducing head motion as a result of physical contact of the transducing head with the data storage medium. The controller can issue a contact status in response to comparing a first plurality of position error signals logged during the first frequency to a second plurality of position error signals logged during the second frequency.

A Perpendicular Magnetic Recording (PMR) head is configured for use in Thermally Assisted Magnetic Recording (TAMR). Two or three contiguous write shields, of various widths and thicknesses, formed on a leading edge side of the write gap (WG), main pole (MP) and near-field transducer (NFT), protect the head during write touchdowns (TD) and signal the approach of such a touchdown. Moreover during a write touchdown the contact with the head is restricted to the large write shields, producing a large touchdown area (TDA) and insuring the lifetime of the head.

According to one embodiment, when an inspection of a defect of a recording surface of the magnetic disk is carried out by using the first processing section and the second processing section on the basis of the output of the gap sensor, a magnetic disk device is configured to compare a threshold defined on the basis of outputs of the first processing section at a plurality of tracks excluding a track which is an inspection object and an output of the first processing section at the track which is the inspection object with each other and, when the output of the first processing section at the track which is the inspection object exceeds the threshold, detect that there is a defect on the track concerned of the magnetic disk.

A recording head has a waveguide that delivers optical energy from an energy source and a write pole extending to a media-facing surface of the recording head. The recording head also has a near-field transducer coupled to receive the optical energy from the waveguide and emit surface plasmons from the media-facing surface towards a recording medium while the write pole applies a magnetic field to the recording medium. The near-field transducer has an extended portion that, as-manufactured, protrudes beyond the media-facing surface by a first distance.

Example systems, data storage devices, and methods to provide long-term spacing compensation for heat assisted magnetic recording 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. The head includes a laser for heat assisted magnetic recording and a fly height actuator. Based on the operation of the laser, both a short-term fly height compensation parameter and a long-term fly height compensation parameter are determined based on different temperature state models. The operating power of the fly height actuator is determined, at least in part, based on the short-term and long-term height compensation parameters.

According to one embodiment, a magnetic disk device includes a magnetic disk, a magnetic head including a read head, a write head, a heater and the magnetic head, and a sensor and the control section. The control section when applying electric power to the heater, the control section predicts, on the basis of a relationship between a value of the electric power to be applied to the heater and an output value of a spectrum at a pulse frequency of a DC output of the sensor in a state where pulsed electric power is applied to the heater, the output value of the spectrum, and detects contact between the magnetic head and the magnetic disk before the predicted output value of the spectrum becomes less than or equal to a threshold.