Abstract:
A novel magnetic imaging microscope test system with high spatial (1-10 nm) and temporal (˜1 ns) resolution of the magnetic field is disclosed, as well as the system application for characterization of read and write heads for magnetic recording. The test system includes a scanner assembly and a work piece holder for holding a work piece to be tested. The scanner assembly and the work piece holder are positionable relative to each other at very fine resolution during scanning. A probe arm is cantilevered from the scanner assembly to bring a probe head into close proximity to the work piece holder. The probe head is configured scan a work piece in contacting engagement therewith so that a magnetic device on the probe head magnetically interacts with a magnetic field generating or magnetic field sensing device on the work piece. A probe head for use in the test system and a related test method are also disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to the field of scanning microscopy. More particularly, the invention concerns the non-intrusive magnetic imaging of devices and systems that generate and/or sense magnetic fields, including the magnetic field output of magnetic write heads and the magnetic response of magnetic read heads.  
           [0003]    2. Description of the Prior Art  
           [0004]    By the way of background, current methods for magnetic imaging suffer from various limitations. The most widespread method is Magnetic Force Microscopy (MFM). Even though MFM provides high spatial resolution, it does not actually measure magnetic field, but rather the magnetic field gradient, making interpretation of the images difficult and, in some cases, impossible to de-convolute. Additionally, MFM only works with static magnetic fields and has no time-domain capabilities. Another wide-spread magnetic imaging method is Kerr microscopy, which does provide time-resolved magnetic field imaging. However, Kerr microscopy can only image magnetization of the material, thus limiting the technique in the choice of materials. Additionally, because Kerr microscopy is an optical technique, the spatial resolution is limited by the wavelength of light. More recent advances in the field of magnetic imaging, such as Lorenz microscopy, ballistic electron emission microscopy, and polarization X-ray microscopy also suffer from various limitations, and are complicated and expensive.  
           [0005]    Accordingly, a need exists for a new technique for magnetic imaging that can provide unambiguous magnetic field mapping with high spatial resolution, and which also preferably provides time-domain capabilities. One area where such a technique could be immediately utilized is the characterization of magnetic recording heads. Although a variety of characterization techniques have been developed in this area, they involve characterization of a more complicated system, which includes not only the head for magnetic recording, but also the magnetic recording media and the electronics for operating the head. In addition to being an indirect method of head characterization, these methods involve long evaluation cycles and the high cost associated with building individual sliders.  
           [0006]    What is therefore required is a magnetic imaging system that allows non-intrusive imaging of magnetic fields with high (e.g., ˜1-10 nm) spatial resolution and high (e.g. ˜1 nsec or better) temporal resolution, and whose functions include imaging the time-resolved magnetic field output of a magnetic write head and imaging the magnetic response of a magnetic read head.  
         SUMMARY OF THE INVENTION  
         [0007]    The foregoing problems are solved and an advance in the art is obtained by a magnetic imaging microscope test system that can be utilized for characterization of read and write heads used for magnetic recording, and for characterization of other structures that are magnetic in nature or which otherwise produce magnetic fields (such as AC current-carrying wires).  
           [0008]    According to the invention, the test system can be operated in two main modes. In the first mode, which may be called imaging mode, a magnetic field sensor is used to raster-scan over the surface of a work piece (test sample) and acquire an image of the magnetic field to be characterized. In the second mode, which may be called stimulation mode, a structure that produces a tunable local magnetic field, referred to herein as a “magnetic stencil,” is used to raster-scan over the surface of a work piece while the magnetic response of the work piece is recorded to form an image.  
           [0009]    The test system further includes a scanner assembly and a work piece holder for holding the work piece to be tested. The scanner assembly and the work piece holder are positionable relative to each other at a coarse resolution, while the image is acquired by scanning at very fine resolution, preferably using piezoelectric scanner. A probe arm is cantilevered from the scanner assembly and extends to a probe arm free end situated adjacent the work piece. A probe head is disposed at the probe arm free end and incorporates a magnetic device comprising either a magnetic field sensor, a magnetic stencil, or both. The test system may further incorporate a laser that focuses a laser beam on the back side of the probe head, which reflects the beam to a detector. The reflected beam is used to adjust the angle between the probe head and the work piece, and with feedback circuitry, can be used to maintain that angle at a pre-determined setting during the scanning, to ensure constant distance between the magnetic device and the work piece surface.  
           [0010]    In the imaging mode of operation, a variety of magnetic sensors can be used. The choice of the sensor is application dependent, and is determined based on whether the in-plane or out-of-plane component of the magnetic field is to be studied, by the magnitude of the magnetic field, and by dynamics of the magnetic field.  
           [0011]    In one exemplary magnetic sensor embodiment, the sensor comprises a magnetic flux pick-up loop having a short section providing a sensor tip portion and a pair of legs extending therefrom to a pair of electrical contacts. An electrically conductive ground plane is spaced from the pick-up loop. This sensor produces output voltage proportional to the magnitude of time-variant magnetic fields introduced into the pick-up loop tip portion in a direction parallel to the work piece surface and perpendicular to the loop plane.  
           [0012]    In another exemplary magnetic sensor embodiment, the sensor comprises a layer of soft ferromagnetic material forming a sensor tip portion sandwiched between layers of non-magnetic electrically conductive material. Operation of this sensor is based on the anisotropic magnetoresistance effect (AMR), and the sensor resistance change is proportional to the magnitude of magnetic fields in a direction parallel to the work piece surface and perpendicular to the sensor layer planes.  
           [0013]    In yet another exemplary magnetic sensor embodiment, the sensor comprises a multilayer structure, similar to the giant-magneto-resistance (GMR) structures used in the read heads for magnetic recording. One edge of the multilayer structure provides a sensor tip portion. According to one construction, the change in resistance of the sensor is roughly proportional to the magnitude of magnetic fields in a direction perpendicular to the work piece surface and parallel to the layer planes. According to another construction, the change in resistance of the sensor is roughly proportional to the magnitude of magnetic fields in a direction parallel to the work piece surface and perpendicular to the layer planes. Other exemplary embodiments, using tunneling magneto-resistance (TMR) and variations of the GMR, TMR, and AMR structures may also be constructed.  
           [0014]    The imaging mode of the test system can be used for characterization of magnetic recording write heads, in which case any of the aforementioned magnetic sensors may be incorporated on the probe head while the test system is operated in the imaging mode to characterize the magnetic output of the field generator. During imaging, an AC write current is applied to the write head at the desired frequency, which is preferably the same frequency at which the head operates in a disk drive for magnetic recording. This results in a time-varying magnetic field being generated at the ABS surface of the write head. By imaging this field, the parameters important for write head evaluation, such as field amplitude, field gradient, erase bands, overwrite, adjacent track interference, and write bubble speed can be determined.  
           [0015]    When the test system is used in the stimulation mode, the probe head may incorporate the aforementioned magnetic stencil to produce a local magnetic field, which, optionally, could be time-dependent.  
           [0016]    In one exemplary magnetic stencil embodiment, the stencil comprises an inductive coil driving a pair of soft magnetic pole pieces, one of which is extended to form a stencil tip. By passing electrical current into the coil, the magnetization of the pole pieces is changed, resulting in a magnetic field being generated from the end of the extended pole piece, perpendicular to the work piece surface. The magnetic field is confined to the cross-sectional size of the extended pole piece.  
           [0017]    In another exemplary magnetic stencil embodiment, the stencil comprises a wire that is used to drive a soft adjacent ferromagnetic layer providing a stencil tip portion. The wire passes an electrical current that alters the magnetic moment of the ferromagnetic layer according to fluctuations in current magnitude and direction. This stencil generates a magnetic field that is perpendicular to the work piece surface and parallel to the ferromagnetic layer plane.  
           [0018]    In still another exemplary magnetic stencil embodiment, the stencil comprises a pair of conductive electrodes, separated by thin insulation layer, with electrical current flowing in opposite directions through the electrodes. Each electrode has a short section providing a stencil tip portion. This results in a magnetic field confinement between the tip portion with the magnetic field emerging from the gap in the direction perpendicular to the work piece surface and parallel to the layer planes.  
           [0019]    The stimulation mode of operation can be applied for characterization of the sensors of magnetic recording read heads. The magnetic stencil is scanned over the read sensor and driven by an AC current while the response of the sensor, i.e. it&#39;s change in resistance, is recorded. By doing so, parameters such as magnetic read track width, amplitude, pulse width at half amplitude (PW50), and position-dependent stability can be determined. By repeating the scans at varied stencil amplitude, position-dependent transfer curves can be obtained, allowing extraction of the sensor stiffness and hard bias properties.  
           [0020]    In each of the foregoing embodiments, the magnetic sensor/stencil may be adapted for operation at a spatial resolution of between approximately 1-10 nm at the adjustable distance from the surface of the sample and a temporal resolution as high as approximately 1 nsec.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0021]    The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying Drawing, in which:  
         [0022]    [0022]FIG. 1 is a schematic view of a magnetic imaging microscope test system constructed in accordance with the present invention;  
         [0023]    [0023]FIG. 2 is a functional block diagram of the test system of FIG. 1;  
         [0024]    [0024]FIG. 3 is a perspective view of a work piece being scanned by the test system of FIG. 1 in a first direction;  
         [0025]    [0025]FIG. 4 is a plan view showing an exemplary probe arm and probe head of the test system of FIG. 1 scanning a disk drive slider row in the first direction;  
         [0026]    [0026]FIG. 5 is an enlarged plan view showing scanning of a slider row read/write head in the first direction;  
         [0027]    [0027]FIG. 6 is a perspective view of a work piece being scanned by the test system of FIG. 1 in a second direction;  
         [0028]    [0028]FIG. 7 is a plan view showing an exemplary probe arm and probe head of the test system of FIG. 1 scanning a disk drive slider row in the second direction;  
         [0029]    [0029]FIG. 8 is an enlarged plan view showing scanning of a slider row read/write head in the second direction;  
         [0030]    [0030]FIG. 9A is a scan image of a magnetic recording write head produced by the magnetic imaging microscope test system of FIG. 1 scanning in the first direction; and  
         [0031]    [0031]FIG. 9B is example of the magnetic field image of another magnetic recording write head produced by the magnetic imaging microscope test system FIG. 1, scanning in the second direction;  
         [0032]    [0032]FIG. 10 is a plan view showing a first exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic sensor for magnetic field generator characterization;  
         [0033]    [0033]FIG. 11 is a perspective view showing a second exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic sensor for magnetic field generator characterization;  
         [0034]    [0034]FIG. 12A is a cross-sectional view showing a third exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic sensor for magnetic field generator characterization;  
         [0035]    [0035]FIG. 12B is a top-down view of the magnetic sensor of FIG. 12A looking toward a work piece to be imaged;  
         [0036]    [0036]FIG. 13A is a cross-sectional view showing a fourth exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic sensor for magnetic field generator characterization;  
         [0037]    [0037]FIG. 13B is a top-down view of the magnetic sensor of FIG. 13A looking toward a work piece to be imaged;  
         [0038]    [0038]FIG. 14A is a cross-sectional view showing a first exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic stencil for magnetic sensor characterization;  
         [0039]    [0039]FIG. 14B is a plan view of the magnetic stencil of FIG. 15A;  
         [0040]    [0040]FIG. 15 is a perspective view showing a second exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic stencil for magnetic sensor characterization; and  
         [0041]    [0041]FIG. 16 is a perspective view showing a third exemplary embodiment of a probe head magnetic device of the test system of FIG. 1 implemented as a magnetic stencil for magnetic sensor characterization. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0042]    Turning now to the figures, wherein like reference numerals represent like elements in all of the several views, FIG. 1 illustrates a magnetic imaging microscope test system  2  adapted for high resolution magnetic characterization of magnetic field generating and sensing devices, and particularly disk drive inductive write heads and magnetoresistive read heads. The test system  2  includes a scanner assembly  4  that is preferably adapted for very finely controllable (e.g., ˜1 nm) resolution) two-dimensional movement in the directions shown by the x and y axes in FIG. 1. A conventional piezoelectric control system of the type used in a standard MFM may be used for this purpose. The scanner assembly  4  includes a piezoelectric assembly  6  that carries a probe arm  8 . The probe arm  8  is cantilevered from the piezoelectric assembly  6  so as to extend toward a work piece  10 . In the context of the present invention, the work piece  10  will comprise a magnetic field generating or sensing device, such as a magnetic disk drive write head or read head, or a collection of such devices arranged in a single slider row or in multiple slider rows on a wafer substrate. The work piece  10  is supported on a stage  12  that acts as a work piece holder and is preferably adapted for gross positioning of the work piece  10  in the directions shown by the x and y axes in FIG. 1.  
         [0043]    A probe head  14  is disposed at the free end of the probe arm  8 . It is configured to slidably engage the work piece  10 , so that a magnetic device  15  incorporated on the probe head (i.e., a magnetic stencil or sensor as described in more detail below) can be operatively positioned for magnetic interaction with the work piece.  
         [0044]    Turning now to FIG. 2, many of the functional components of a conventional MFM scanning assembly may be used to implement the electronics of the test system  2 , while others are external. These components include a signal generator  20 , an RF lock-in amplifier  22 , a broadband amplifier  24 , an x-y scanning piezo driver system  26 , and a data processing system such as a computer workstation  28 . In the embodiment of FIG. 2, the work piece  10  comprises magnetic field generators, which, for example, could be one or more disk drive write heads  11 . The signal generator  20  generates an appropriate test (stimulus) signal  30 , such as a sine wave AC current, to drive the write head  11  to generate a corresponding alternating magnetic field signal. The signal generator  20  also generates a reference signal  32  that is locked in frequency and phase to the stimulus signal  30  and is fed to the reference input of the RF lock-in amplifier  22 .  
         [0045]    The magnetic device  15  on the probe head  14  is assumed to be a magnetic sensor to generate a readback signal  34  in response to the magnetic fields generated by the write head  11 . The readback signal  34  is amplified by the broadband amplifier  24  and fed to the second input of the RF lock-in amplifier  22 . The RF lock-in amplifier  22  compares the reference signal  32  and the readback signal  34  and outputs a characterizing signal  36  representing the time-varying magnetic output of the write head  11 . The characterizing signal  36  is converted to digital form by an analog-to-digital (A-D) converter  38 , and fed to the workstation  28  for evaluation. It will be appreciated that if the frequency (or time) characteristics of the write head  11  are not necessary, a static imaging can be obtained by removing the stimulus signal  30 , and only analyzing the average value of the signal  34 . It will be further appreciated that the signal generator  20  and the lock-in amplifier  22  could be replaced by a network analyzer. Alternatively the lock-in amplifier  22  could be replaced by digitizing scope, or any other detection device, as determined by the noise level of the system.  
         [0046]    In order to test different areas of the write head  11 , the workstation  28  generates x and y positioning signals  40  and  42  that are respectively converted to analog form by digital-to-analog (D-A) converters  44  and  46  forming part of the x-y scanning system  26 . A pair of high voltage amplifiers  48  and  50 , also forming part of the x-y scanning system  26 , produce high voltage x and y driving signals  52  and  54  that are used to control the position of the scanner assembly  4  relative to the write head  11 . Coarse positioning of the scanner assembly  4  relative to a work piece is performed by the adjusting the x-y positioning stage  12 .  
         [0047]    Although FIG. 2 illustrates an implementation of the test system  2  that can be used to characterize magnetic field generators, such as magnetic recording write heads, it will be appreciated that the system could be readily adapted to characterize magnetic field sensors, such as magnetic recording read heads, by connecting the signal generator  20  to drive the probe head  14  and connecting the work piece  10  to the broadband amplifier  24 . Moreover, in this configuration the magnetic device  15  of the probe head  14  would comprise a magnetic stencil, either in lieu of a magnetic sensor or in combination therewith.  
         [0048]    Turning now to FIG. 3, one of the features that differentiates the test system  2  from a conventional MFM device is that the probe head  14  is generally large and rectangular, as opposed to the point contact configuration of a conventional MFM probe tip. As a consequence, only topographically flat surfaces can be imaged. However, this provides an advantage in that the feedback mechanism is significantly simplified compared to an MFM, where the feedback circuitry is required to maintain constant separation between the MFM tip and the sample surface. This facilitates a much simpler test procedure and drastically faster scan rates. Moreover, unlike an MFM, the probe head  14  can incorporate a magnetic device  15  that comprises either a magnetic sensor or a magnetic stencil (as described in more detail below) or both, as well as a variety of other lithographically defined structures. This allows the test system  2  to measure magnetic fields instead of just magnetic field gradients, and further allows for dynamic characterization at desired frequencies as well as characterization in different magnetic directions.  
         [0049]    In FIG. 3, the work piece  10  is shown to comprise a linear collection of magnetic field generating and/or sensing devices. The work piece  10  is arranged relative to the probe arm  8  such that the magnetic device  15  may be used to image a particular magnetic field direction. As scanning is performed, the electronics of the test system  2  are used to characterize the magnetic properties of the work piece devices.  
         [0050]    Note that the work piece  10  may be scanned with the probe head&#39;s magnetic device  15  in contacting engagement with the work piece  10  or with the magnetic device spaced from the work piece  10 . To maintain a constant separation distance, a conventional laser driver  50  and a laser detector  52  of the type used in MFM systems may be used to detect the angle between the probe head  14  and the work piece  10 . As shown in the inset in FIG. 3, the magnetic device  15  is offset a small distance “d” (e.g., 0.1-10 um) from the trailing edge of the probe head  14 . At an angle ∂ formed by the work piece  10  and probe head  14 , the separation of the magnetic device  15  from the work piece surface is equal to d*sin (∂). Therefore, by maintaining a selected angle ∂, the magnetic device  15  of the probe head  14  can be scanned at a desired height above the work piece surface.  
         [0051]    [0051]FIG. 4 illustrates a practical use for the scanning orientation of FIG. 3 in an exemplary embodiment of the invention in which the probe arm  8  is formed using a conventional disk drive suspension assembly  60  and wherein the magnetic device  15  is formed as a thin film structure on a conventional disk drive slider  62  (which serves as the probe head  14 ). The magnetic device  15  is raster-scanned across a slider row  64  that mounts a plurality of magnetic recording heads  66 . The primary scanning direction is in the direction shown by the arrow  68 . The secondary scanning direction is perpendicular to the arrow  68 . The term “raster scanning” refers to the fact that for each scanning position in the primary scanning direction, a perpendicular scan is performed to acquire a series of scanned lines in the secondary scanning direction, in a manner that is analogous to a raster display device.  
         [0052]    [0052]FIG. 5 illustrates this scanning motion by the magnetic device  15  across a magnetic recording head  66  having a read head  70  and a write head  72 . The primary direction of scanning movement (arrow  68 ) is across the track width of the head  66 . The secondary direction of scanning movement is across the gap width of the head  66 , as shown by the arrow  74 . This kind of scanning facilitates cross-track magnetic profiles that can be used to assess various write head and read head parameters. For example, write heads may be characterized for write width, erase band width, write bubble speed, overwrite (OW), outside and inside diameter non-linear transition shifts (NLTS), and cross-track signal-to-noise ratio (SNR) degradation. Read heads may be characterized for read head transfer curve capability, magnetic read width and magnetic side reading.  
         [0053]    Turning now to FIG. 6, the work piece  10 , which is again shown as a linear collection of magnetic field generating and/or sensing devices, is arranged relative to the probe arm  8  such that the magnetic device  15  may be used to raster scan the work piece along its transverse axis. As described above in connection with FIG. 5, the angle ∝ of the probe head  14  is maintained using the laser  50  and detector  52  to provide a desired spacing distance between the magnetic device  15  and the work piece  10 .  
         [0054]    [0054]FIG. 7 illustrates a practical use for the scanning orientation of FIG. 6 in an exemplary embodiment of the invention in which the probe arm  8  is again formed using a conventional disk drive suspension assembly  90  and wherein the magnetic device  15  is formed as a thin film structure on a conventional disk drive slider  92  (which serves as the probe head  14 ). The magnetic device  15  is raster-scanned across a slider row  94  that mounts a plurality of magnetic recording heads  96 . As shown by the arrow  98 , the primary scanning direction is across individual sliders of the slider row  94 . The secondary scanning direction is perpendicular to the arrow  98 .  
         [0055]    [0055]FIG. 8 illustrates this scanning motion by the magnetic device  15  across a magnetic recording head  96  having a read head  100  and a write head  102 . The primary direction of scanning movement is across the gap width of the head  96  (arrow  98 ) while the secondary direction of scanning movement is across the track width of the head, as shown by the arrow  104 . This kind of scanning facilitates additional magnetic profiles that can be used to assess various write head and read parameters. For example, write heads may be characterized for gap field at product data rates. Read heads may be characterized for 50% amplitude pulse width (PW 50) and user bit density (PW50/T) measurements.  
         [0056]    As a demonstration of the foregoing scanning techniques, FIGS. 9A and 9B show two images of the magnetic field produced by a conventional disk drive write head at 1 MHz as measured by the test system  2  in the imaging mode and with the magnetic device  15  comprising a magnetic sensor. FIG. 9A shows the magnetic image of the P1 pole  80  and P2 pole  82  when scanned in the direction shown in FIGS.  3 - 5 . A pair of S1 and S2 shields  84  and  86  can also be seen, as well as the formation of magnetic domains  88  in the P1 pole  80 . In FIG. 9B, the scanning direction is as shown in FIGS.  6 - 8 . It is revealed that the strongest magnetic field is produced by the P2 pole  80 , while the P1 pole  82  and the shields  84  and  86  have a smaller field of opposite polarity.  
         [0057]    Turning now to FIGS.  10 - 13 , exemplary implementations of the magnetic device  15  as magnetic sensor structures for the imaging mode of the test system  2  are shown. In FIG. 10, an exemplary magnetic sensor  110  is formed by a conductive back plane structure  112  made from copper or the like, upon which are formed a flux pickup loop  114  made from a conductive material such as Cu or the like. A gap  116  between the legs of the pickup loop  114  may be in range of 1-50 nm. A short section  118  of the pickup loop  114  can be lapped to provide a sensor tip portion having a stripe height of about 5-10 nm. Time-variant magnetic fields in a direction perpendicular to the plane of the pickup loop  114  and parallel to the surface of the work piece  10  (as shown by the arrow head/tail  122 ) cause electrical current flow in the loop, which is then sensed through the electric terminals  120  of the sensor  110 . Advantageously, only flux changes in the area of the pickup loop  114  close to the sensor tip portion  118 , which is not backed up by the conductive plane  112 , are detected. Thus, high spatial resolution of local magnetic fields can be achieved.  
         [0058]    In FIG. 11, another exemplary magnetic sensor  130  is formed by sandwiching a soft ferromagnetic material layer  132 , such as NiFe, CoFe or the like, between two planar conductive leads  134  made from copper or the like, that are otherwise electrically insulated from each other by an insulating layer (not shown) such as Al2O3, SiO2 or the like. Electrical current goes through the leads  134  and passes through the ferromagnetic layer  132 , which forms a tip portion of the sensor  130 . Resistance of the sensor  130  depends on the magnetization of the ferromagnetic layer  132  with respect to the current flowing direction according to AMR effect in the current perpendicular to plane (CPP) configuration. For the sensor  130 , this direction is perpendicular to the sensor deposition plane (i.e., the direction shown by the arrow  136  in FIG. 11) and parallel to the surface of the work piece  10 . This is intentionally chosen to give several advantages. First, because the current is flowing perpendicular to the deposition plane, the sensor  130  is sensitive only to the X-component of the magnetic field (i.e., in the direction of the arrow  136 ), and does not change its resistance state even when the sensor&#39;s in-plane magnetization is changing. Second, the sensor  130  has linear response even in large magnetic fields, because it has a very large de-magnetization factor in the direction perpendicular to the deposition plane. The high spatial resolution is obtained by the fact that the thickness of the ferromagnetic layer  132  is 1-10 nm, and its lateral dimensions can be made about 10-30 nm by utilizing E-beam lithography. Additionally, the sensor  130  is lapped so that the ferromagnetic layer  132  has a stripe height of 5-10 nm.  
         [0059]    In FIGS. 12A and 12B, another exemplary magnetic sensor  140  is shown. This multilayer structure is similar to the GMR sensors of magnetic recording read heads. It includes an anti-ferromagnetic pinning layer  142  made from PtMn or the like, a multilayer pinned structure comprising a first pinned layer  144  made from CoFe or the like, a non-magnetic spacing layer  146  made from Ru or the like, and a second pinned layer  148  made from CoFe or the like, a conductive spacer layer  150  made from Cu or the like, and a free sensing layer  152  made from NiFe or the like. An electrical sense current may be passed through the conductive leads  154  abutted to the pattern multilayer, and changes in resistance are proportional to the sin of the angle between the free layer  152  and the second pinned layer  148 . The magnetization of the pinned layers  144  and  148  is pinned in the deposition plane perpendicular to the sensor&#39;s tip portion  156 . By using E-beam lithography, the size of the sensor  140  can be made on the order of 10-30 nm, which determines the resolution of the sensor. The  140  sensor is sensitive to the out-of-plane component of the magnetic field parallel to the deposition planes and perpendicular to the surface of the work piece  10  (as shown by the arrow  158  in FIGS. 12A and 12B). Sensor structures similar to sensor shown in FIGS. 12A and 12B can also be made utilizing tunnel magneto-resistance effect (TMR).  
         [0060]    In FIGS. 13A and 13B another sensor  160 , also based on the GMR effect, is shown. The sensor  160  includes a pinning layer  162  made form PtMn or the like, a multilayer pinned structure  164  comprising CoFe and Ru layers, a spacer layer  166  made from Cu or the like, and a free layer  168  made from NiFe or the like. The sensor is abutted by a pair of conductive leads  170 . Unlike the pinned layers of the sensor  140  shown in FIGS. 12A and 12B, the magnetization of the pinned multilayer structure  164  is pinned perpendicular to the deposition plane and parallel to the sensor&#39;s tip portion  172 . This is achieved by utilizing high out-of-plane anisotropy of the multilayer CoFe pinned layers when their thickness is made on the order of 4-6 Angstroms. As such, the sensor  160  will be sensitive to a magnetic field perpendicular to the sensor deposition planes and parallel to the surface of the work piece  10  (i.e., in the direction of the arrow  174 ). Sensor structures similar to sensor shown in FIGS. 13A and 13B can also be made utilizing tunnel magneto-resistance effect (TMR).  
         [0061]    In addition to forming the magnetic device  15  so as to include any of the foregoing magnetic sensors, it should be noted that is possible to combine on the same magnetic sensor structure more than one sensor, such that one will be sensitive to the in-plane component of the magnetic field, and the other to the out-of-plane component of the magnetic field. By recording the response of both sensors individually, all components of the magnetic field can be mapped.  
         [0062]    Turning now to FIGS.  14 - 16 , exemplary implementations of the magnetic device  15  as magnetic stencils for use during the stimulation mode of the test system  2  are shown. In FIG. 14A, a magnetic stencil  180  is formed as a modified write head. The stencil  180  thus includes a plurality of coil loops  182  made from copper or the like that drive a yoke  184  made from a soft ferromagnetic material such as NiFe (permalloy), CoFe or other materials. The yoke  184  includes a pair of soft magnetic pole pieces  186  and  188 , with the pole piece  186  being extended to form a stencil tip  190 . The coil loops  182  and the yoke  184  are embedded in an insulative material  192 , such as alumina (Al 2 O 3 ), that is deposited over a suitable substrate  194 . The stencil tip  190  is lithographically defined by the lift-off or by the ion-mill technique on a vacuum-deposited layer of soft ferromagnetic material, such as NiFe or the like. The thickness of the deposited material can be finely controlled to within few angstroms, with the total thickness preferably in the range of 1-10 nm. In the top-down view of FIG. 14B, the width of the stencil tip  190  is defined lithographically, and can be in the range of 10 nm to 100 um.  
         [0063]    By passing electrical current into the coil loops  182 , the magnetization of the pole pieces  186  and  188  is changed, resulting in a magnetic field being generated from the end of the stencil tip  190 , perpendicular to the surface of the work piece  10  (i.e., the direction of the arrow  196 ). The magnetic field is confined to the cross-sectional size of the stencil tip structure. Because the magnetic field is localized to the space near the stencil tip  190 , the very fine stencil tip thickness permits very high resolution in the primary scanning direction shown by the arrow  198 . On the other hand, the stencil tip  190  can be made relatively wide in the perpendicular secondary scanning direction (e.g., about 10-100 um), for ease of alignment of the magnetic device  15  relative to the work piece  10 , which could be a magnetic recording read head.  
         [0064]    In FIG. 15, a magnetic stencil  200  is formed using another design alternative in which a wire  202  is lithographically processed from copper or the like is used to drive a soft adjacent layer  204  made from a soft ferromagnetic material such as NiFe, CoFe or the like. The soft adjacent layer  204  provides a tip portion of the stencil  200 . The wire  202  passes a current “I” that alters the magnetic moment “M” of the soft adjacent layer  204  according to fluctuations in current magnitude and direction. Note that the direction of the magnetic moment “M” in the quiescent state can be oriented as shown in FIG. 200. The stencil generates a magnetic field that is perpendicular to the surface of the work piece  10  (i.e., the direction of the arrow  206 ). When the stencil is placed in an operative position with the layer plane normal to the work piece  10 , the magnetic field will be parallel to the work piece surface. Advantageously, the soft adjacent layer  204  has a very narrow thickness of approximately 1-10 nm, thus permitting very high resolution in the primary scanning direction (shown by the arrow  208 ). On the other hand, the soft adjacent layer  204  is preferably relatively wide in the perpendicular secondary scanning direction (e.g., about 10-100 um), for ease of alignment of the magnetic device  15  relative to the work piece  10 , but could be made using E-beam lithography as narrow as ˜10 nm for applications requiring two-dimensional imaging.  
         [0065]    In FIG. 16, a magnetic stencil  210  is formed using another design alternative featuring a pair of inductive coil loops  212  and  214 , made from copper or the like. Each coil loop  212  and  214  passes a current I of equal magnitude but of opposite direction, and has a short section  216  providing a stencil tip portion. The coil loops  212  and  214  are separated by a suitable insulator, such as alumina, that defines a gap thickness “G.” Advantageously, the gap “G” is very narrow (e.g., approximately 1-10 nm), thus permitting very high resolution in the primary scanning direction shown by the arrow  218 . On the other hand, the width of each coil loop section  216  is preferably relatively wide in the perpendicular secondary scanning direction (e.g., about 10 um), for ease of alignment of the magnetic device  15  relative to the work piece  10 . The electrical current passing through the coil loops  212  and  214  creates a magnetic field oriented parallel to the stencil layer planes and perpendicular to the work piece  10  (i.e., the direction of the arrow  220 ).  
         [0066]    Accordingly, a magnetic imaging microscope test system has been disclosed. Additionally, its use for characterization of read and write heads used for magnetic recording has been described. While various embodiments of the invention have been described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.