Magneto-optical detection of a field produced by a sub-resolution magnetic structure

Abstract

A polarization microscope optically detects the effect of the magnetic field from a sub-optical resolution magnetic structure on a magneto-optical transducer. The magneto-optical transducer includes a magnetic layer with a magnetization that is changed by the magnetic field produced by the magnetic structure. The saturation field of the magnetic layer is sufficiently lower than the magnetic field produced by the magnetic structure that the area of magnetization change in the magnetic layer is optically resolvable by the polarization microscope. A probe may be used to provide a current to the sample to produce the magnetic field. By analyzing the optically detected magnetization, one or more characteristics of the sample may be determined. A magnetic recording storage layer may be deposited over the magnetic layer, where a magnetic field produced by the sample is written to the magnetic recording storage layer to effect the magnetization of the magnetic layer.

What is claimed is: 
     
         1 . An apparatus for testing a sample that includes a magnetic field producing structure, the apparatus comprising:
 a polarization microscope including an optical detector, an optical axis, and a field of view, the polarization microscope having an optical resolution limit, wherein the largest linear dimension of the projection of the magnetic field producing structure of the sample on a plane perpendicular to the optical axis is smaller the optical resolution limit;   a magneto-optical transducer comprising a magnetic layer having a magnetization and a saturation field, the magneto-optical transducer being positioned on the optical axis and within the field of view of the polarization microscope, the polarization microscope optically detects a change in the magnetization of the magnetic layer;   a reflective layer coupled to the magnetic layer, wherein the sample under test is held so that the reflective layer is between the magnetic layer and the magnetic field producing structure and so that the magnetic layer is between the magnetic field producing structure and the optical detector; and   wherein the saturation field of the magnetic layer is sufficiently lower than a magnetic field produced by the magnetic field producing structure that a change in the magnetization of the magnetic layer is produced over an area with a linear dimension that is larger than the optical resolution limit of the polarization microscope.   
     
     
         2 . The apparatus of  claim 1 , wherein the magneto-optical transducer comprises at least one of a soft underlayer magnetic film and a magnetic recording layer deposited on the reflective layer so that the at least one of the soft underlayer magnetic film and the magnetic recording layer is between the reflective layer and the magnetic field producing structure of the sample under test. 
     
     
         3 . The apparatus of  claim 2 , wherein the magneto-optical transducer further comprises a magnetic recording storage layer deposited on the soft underlayer magnetic film so that the magnetic recording storage layer is between the soft underlayer magnetic film and the magnetic field producing structure of the sample under test. 
     
     
         4 . The apparatus of  claim 1 , wherein the reflective layer is a soft underlayer magnetic film deposited on the magnetic layer. 
     
     
         5 . The apparatus of  claim 1 , wherein the reflective layer is a magnetic recording storage layer deposited on the magnetic layer. 
     
     
         6 . The apparatus of  claim 1 , wherein the reflective layer is a surface on the sample under test. 
     
     
         7 . The apparatus of  claim 1 , further comprising a probe configured to be coupled to the sample to provide a current to cause the magnetic field generating structure in the sample to produce the magnetic field. 
     
     
         8 . The apparatus of  claim 7 , wherein the probe is configured to be coupled to a sample that includes a write head, wherein the magnetic field producing structure of the sample is a write pole. 
     
     
         9 . The apparatus of  claim 8 , wherein the sample is in the form of one of a bar, slider, head gimbal assembly or head stack assembly. 
     
     
         10 . The apparatus of  claim 7 , wherein the probe is coupled to a current supply that is configured to provide a positive current, a negative current, a pulsed current, and a varying current, to the sample via the probe. 
     
     
         11 . The apparatus of  claim 7 , wherein the sample includes a write head and the probe is further configured to provide a current to a Dynamic Flying Height device on the sample. 
     
     
         12 . The apparatus of  claim 7 , wherein the sample includes a write head and the probe is further configured to provide a current to a microactuator device on the sample. 
     
     
         13 . The apparatus of  claim 7 , wherein the sample includes a heat assisted magnetic recording write head and the probe is further configured to provide a current to a thermal device on the sample. 
     
     
         14 . The apparatus of  claim 1 , wherein the sample includes a heat assisted magnetic recording write head, the apparatus further comprising a laser used with a heat assisted magnetic recording write head. 
     
     
         15 . The apparatus of  claim 1 , wherein the largest linear dimension of the projection of the magnetic field producing structure is smaller than 275 nm and the area of change in magnetization of the magnetic layer has a diameter of 275 nm or greater. 
     
     
         16 . The apparatus of  claim 1 , wherein the polarization microscope is one of a white field microscope and a confocal microscope. 
     
     
         17 . The apparatus of  claim 1 , wherein the optical detector is one of a camera and a photodetector. 
     
     
         18 . The apparatus of  claim 1 , wherein the magnetic layer comprises ferrimagnetic garnet. 
     
     
         19 . The apparatus of  claim 18 , wherein the saturation field of the magnetic layer is at least one order of magnitude lower than the magnetic field produced by the magnetic field producing structure of the sample. 
     
     
         20 . The apparatus of  claim 1 , wherein the magnetic layer comprises at least one of NiFe, Ni, NiCr, CoFe, NiFeCr, and CoNiFe. 
     
     
         21 . The apparatus of  claim 1 , wherein the magneto-optical transducer is positioned so that the detected magnetization component of the magnetic layer is along the optical axis. 
     
     
         22 . The apparatus of  claim 1 , further comprising a processor coupled to the polarization microscope, the processor is configured to receive an image of the magnetization of the magnetic layer from the optical detector and to analyze the image to determine a characteristic of the sample. 
     
     
         23 . The apparatus of  claim 22 , wherein the determined characteristic of the sample is a geometrical dimension of the sample. 
     
     
         24 . The apparatus of  claim 22 , wherein the determined characteristic of the sample is the strength of the magnetic field produced by the magnetic field generating structure in the sample. 
     
     
         25 . The apparatus of  claim 22 , further comprising a probe configured to be coupled to the sample to provide a current to cause the magnetic field generating structure in the sample to produce the magnetic field, wherein the determined characteristic of the sample is determined for different currents provided to the sample by the probe. 
     
     
         26 . The apparatus of  claim 22 , wherein the determined characteristic of the sample is determined by comparing the image of the magnetization of the magnetic layer to at least one of a threshold and a reference image. 
     
     
         27 . The apparatus of  claim 1 , further comprising a loader that holds at least a portion of the sample flat against the reflective layer or a layer that is disposed over the reflective layer. 
     
     
         28 . The apparatus of  claim 27 , wherein the loader includes an actuator to tilt or pitch the sample to hold the magnetic field producing structure flat against one of the reflective layer and the layer that is disposed over the reflective layer. 
     
     
         29 . The apparatus of  claim 27 , wherein the loader holds a plurality of samples flat against the one of the reflective layer and the layer that is disposed over the reflective layer, the apparatus further comprising a plurality of probes to be coupled to the plurality of samples. 
     
     
         30 . The apparatus of  claim 28 , wherein the loader and the polarization microscope are configured to place at least a subset of the plurality of samples within the field of view simultaneously. 
     
     
         31 . The apparatus of  claim 1 , further comprising a cleaner that is configured to clean the magneto-optical transducer. 
     
     
         32 . The apparatus of  claim 1 , wherein the magneto-optical transducer includes the reflective layer that is deposited on the magnetic layer and wherein a protective layer is deposited on the reflective layer. 
     
     
         33 . The apparatus of  claim 1 , further comprising a fastener for holding the sample on the magneto-optical transducer and a loader that the magneto-optical transducer is loaded onto and held within the field of view of the polarization microscope while the sample is held on the magneto-optical transducer. 
     
     
         34 . The apparatus of  claim 33 , wherein the fastener is one of a mechanical fastener and an adhesive fastener. 
     
     
         35 . The apparatus of  claim 1 , further comprising a reference magnetic field source having a known size and a magnetic field with a known strength and the magnetic field from the reference magnetic field source causes a change in magnetization over an area in the magnetic layer that is detected by the polarization microscope. 
     
     
         36 . The apparatus of  claim 1 , further comprising a temperature control device configured to control the temperature of the sample. 
     
     
         37 . The apparatus of  claim 1 , further comprising a controllable magnetic field source that provides an external magnetic field to at least one of the sample and the magneto-optical transducer. 
     
     
         38 . The apparatus of  claim 1 , further comprising an actuator coupled to at least one of the magneto-optical transducer and the polarization microscope, the actuator provides relative motion between the magneto-optical transducer and the polarization microscope. 
     
     
         39 . The apparatus of  claim 1 , the magnetic layer having a thickness and a saturation field, the thickness and the saturation field of the magnetic layer are configured so that a magnetic field produced by the sample changes the magnetization in the magnetic layer but does not fully saturate through the thickness of the magnetic layer at any location of the magnetic layer. 
     
     
         40 . An apparatus for testing a sample that produces a magnetic field, the apparatus comprising:
 a polarization microscope including an optical detector, the polarization microscope having an optical axis, and a field of view; and   a magneto-optical transducer comprising a magnetic layer and a magnetic recording storage layer deposited over the magnetic layer wherein the sample under test is held so that the magnetic recording storage layer is between the magnetic layer and the sample and the magnetic layer is between the sample under test and the optical detector, the magneto-optical transducer being positioned on the optical axis and within the field of view of the polarization microscope, the polarization microscope optically detects a change in the magnetization of the magnetic layer caused by a magnetic field produced at least one of the sample under test and the magnetic recording storage layer.   
     
     
         41 . The apparatus of  claim 40 , wherein the magneto-optical transducer further comprises a soft underlayer magnetic film deposited between the magnetic layer and the magnetic recording storage layer. 
     
     
         42 . The apparatus of  claim 40 , wherein the magneto-optical transducer further comprises a reflective layer deposited between the magnetic layer and the magnetic recording storage layer. 
     
     
         43 . The apparatus of  claim 40 , wherein the magnetic recording storage layer is reflective. 
     
     
         44 . The apparatus of  claim 40 , the magnetic layer having a magnetization and a saturation field, the saturation field of the magnetic layer being sufficiently lower than the magnetic field produced at least one of the sample under test and the magnetic recording storage layer that a change in the magnetization of the magnetic layer is produced over an area with a linear dimension that is larger than an optical resolution limit of the polarization microscope. 
     
     
         45 . The apparatus of  claim 40 , further comprising a probe configured to be coupled to the sample to provide a current to cause the sample to produce the magnetic field. 
     
     
         46 . The apparatus of  claim 45 , wherein the probe is configured to be coupled to a sample that includes a write head. 
     
     
         47 . The apparatus of  claim 46 , wherein the sample is in the form of one of a bar, slider, head gimbal assembly or head stack assembly. 
     
     
         48 . The apparatus of  claim 45 , wherein the probe is coupled to a current supply that is configured to provide a positive current, a negative current, a pulsed current, and a varying current, to the sample via the probe. 
     
     
         49 . The apparatus of  claim 45 , wherein the sample includes a write head and the probe is further configured to provide a current to a Dynamic Flying Height device on the sample. 
     
     
         50 . The apparatus of  claim 45 , wherein the sample includes a write head and the probe is further configured to provide a current to a microactuator device on the sample. 
     
     
         51 . The apparatus of  claim 45 , wherein the sample includes a heat assisted magnetic recording write head and the probe is further configured to provide a current to a thermal device on the sample. 
     
     
         52 . The apparatus of  claim 45 , wherein the sample includes a heat assisted magnetic recording write head, the apparatus further comprising a laser used with a heat assisted magnetic recording write head. 
     
     
         53 . The apparatus of  claim 40 , wherein the polarization microscope is one of a white field microscope and a confocal microscope. 
     
     
         54 . The apparatus of  claim 40 , wherein the optical detector is one of a camera and a photodetector. 
     
     
         55 . The apparatus of  claim 40 , wherein the magnetic layer comprises ferrimagnetic garnet. 
     
     
         56 . The apparatus of  claim 55 , wherein the saturation field of the magnetic layer is at least one order of magnitude lower than the magnetic field produced by the sample. 
     
     
         57 . The apparatus of  claim 40 , wherein the magnetic layer comprises at least one of NiFe, Ni, NiCr, CoFe, NiFeCr, and CoNiFe. 
     
     
         58 . The apparatus of  claim 40 , wherein the magneto-optical transducer is positioned so that the detected magnetization component of the magnetic layer is along the optical axis. 
     
     
         59 . The apparatus of  claim 40 , further comprising a processor coupled to the polarization microscope to receive an image of a magnetization of the magnetic layer from the optical detector, the processor analyzes the image to determine a characteristic of the sample. 
     
     
         60 . The apparatus of  claim 59 , wherein the determined characteristic of the sample is a geometrical dimension of the sample. 
     
     
         61 . The apparatus of  claim 59 , wherein the determined characteristic of the sample is the strength of the magnetic field produced by the magnetic field generating structure in the sample. 
     
     
         62 . The apparatus of  claim 59 , further comprising a probe configured to be coupled to the sample to provide a current to cause sample to produce the magnetic field, wherein the determined characteristic of the sample is determined for different currents provided to the sample by the probe. 
     
     
         63 . The apparatus of  claim 59 , wherein the determined characteristic of the sample is determined by comparing the image of the magnetization of the magnetic layer to at least one of a threshold and a reference image. 
     
     
         64 . The apparatus of  claim 40 , further comprising a loader that holds at least a portion of the sample flat against the magnetic recording storage layer or a layer that is disposed over the magnetic recording storage layer. 
     
     
         65 . The apparatus of  claim 64 , wherein the loader includes an actuator to tilt or pitch the sample to hold the magnetic field producing structure flat against the magnetic recording storage layer or a layer that is disposed over the magnetic recording storage layer. 
     
     
         66 . The apparatus of  claim 64 , wherein the loader holds a plurality of samples flat against the magnetic recording storage layer or a layer that is disposed over the magnetic recording storage layer, the apparatus further comprising a plurality of probes to be coupled to the plurality of samples. 
     
     
         67 . The apparatus of  claim 65 , wherein the loader and the polarization microscope are configured to place at least a subset of the plurality of samples within the field of view simultaneously. 
     
     
         68 . The apparatus of  claim 40 , further comprising a cleaner that is configured to clean the magneto-optical transducer. 
     
     
         69 . The apparatus of  claim 40 , wherein the magneto-optical transducer further comprises a protective layer deposited on the magnetic recording storage layer. 
     
     
         70 . The apparatus of  claim 40 , further comprising a fastener for holding the sample on the magneto-optical transducer and a loader that the magneto-optical transducer is loaded onto and held within the field of view of the polarization microscope while the sample is held on the magneto-optical transducer. 
     
     
         71 . The apparatus of  claim 70 , wherein the fastener is one of a mechanical fastener and an adhesive fastener. 
     
     
         72 . The apparatus of  claim 40 , further comprising a reference magnetic field source having a known size and a magnetic field with a known strength and the magnetic field from the reference magnetic field source causes a change in magnetization over an area in the magnetic layer that is detected by the polarization microscope. 
     
     
         73 . The apparatus of  claim 40 , further comprising a temperature control device configured to control the temperature of the sample. 
     
     
         74 . The apparatus of  claim 40 , further comprising a controllable magnetic field source that provides an external magnetic field to at least one of the sample and the magneto-optical transducer. 
     
     
         75 . The apparatus of  claim 40 , further comprising an actuator coupled to at least one of the magneto-optical transducer and the polarization microscope, the actuator provides relative motion between the magneto-optical transducer and the polarization microscope. 
     
     
         76 . The apparatus of  claim 40 , the magnetic layer having a thickness and a saturation field, the thickness and the saturation field of the magnetic layer are configured so that a magnetic field produced by the sample changes the magnetization in the magnetic layer but does not fully saturate through the thickness of the magnetic layer at any location of the magnetic layer.