W0 03/021579
`
`-.
`
`10/415751
`
`PCT/US02/27327
`
`i new PCT/PTO 30 APR 2003
`
`-c
`
`Magnetic Material Structures, Devices And Methods
`BACKGROUND OF THE INVENTION
`
`1.
`
`Field of the Invention
`
`_
`
`This invention is directed to magnetic material
`
`structures, methods for making magnetic material structures
`and devices made from magnetic material structures.
`2. Description of the Prior Art
`
`10
`
`15
`
`As
`
`the home, office,
`
`transportation system, business
`
`place and factory become more automated and electronically
`
`connected, and as electronic devices and appliances such as
`
`communication
`communication‘ devices, wireless
`computers,
`devices, electronic games, entertainment systems, personal
`
`data assistants,
`
`transportation vehicles, manufacturing
`
`tools,
`
`shop
`
`tools,
`
`and
`
`home
`
`appliances
`
`become more
`
`sophisticated" there is-,~ and will be,
`
`an ever-increasing
`
`low cost electronic
`and
`for higher performance
`demand
`circuits,
`sensors,
`transducers, data storage systems and
`
`20
`
`other magnetic devices which employ magnetic thin film
`materials.
`In
`order
`for
`these
`devices
`to
`remain
`
`competitive‘ in the market place‘ each product generation
`
`must be higher performing, unobtrusive and, usually,
`
`less
`
`expensive
`
`than
`
`the previous.
`
`Hence
`
`there
`
`are
`
`ever
`
`25
`
`improvements
`technical
`for
`increasing demands
`materials and structure of these devices.
`
`in the
`
`30
`
`35
`
`For all of
`
`these applications the magnetic material
`
`has an improved performance if the magnetic properties can
`
`be better controlled during the construction.
`
`Two familiar
`
`properties, which are sometimes considered to be intrinsic
`
`magnetic properties, are the saturation magnetization, Ms,
`and
`the magnetocrystalline
`anisotropy
`energy
`density
`constants (usually denoted by a subscripted K symbol).
`The
`
`meaning
`
`of magnetic
`
`anisotropy
`
`energy
`
`is
`
`that
`
`the
`
`magnetization would
`
`have
`
`a
`
`preferred
`
`direction,
`
`or
`
`directions, of orientation.
`
`That
`
`is,
`
`the energy of
`
`the
`
`system is minimal when
`
`the magnetization vector points
`
`along certain directions. These directions are referred to
`as
`the magnetic easy axes while the magnetic hard axes
`
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`TDK Corporation Exhibit 1002 Page 1
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`

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`W0 03/021579
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`PCT/US02/2 7327
`
`coincide with. magnetic orientations where the energy is
`
`maximized.
`
`However,
`
`it should be noted that
`
`the magnetic
`
`anisotropy is not actually an intrinsic property in the
`sense that
`the materials are commonly not made perfectly.
`
`5 Nevertheless,
`
`good performance in device applications is
`
`3‘
`
`almost always dependent upon there being a single preferred
`
`magnetic orientation or anisotropy direction and so in the
`
`manufacturing process one strives to achieve
`
`a desired
`
`uniaxial anisotropy. An objective of the present
`
`invention
`
`10
`
`is
`
`to
`
`provide
`
`new mechanisms
`
`for
`
`controlling
`
`the
`
`magnetocrystalline anisotropy of
`
`thin magnetic films. By
`
`doing so the performance of almost all magnetic devices are
`envisioned to be improved.
`
`In general
`orientation of
`
`the anisotropy energy is a function of the
`the magnetization vector with respect
`to a
`
`15
`
`given physical
`
`axis.
`
`Here,
`
`we define
`
`a- “uniaxial"
`
`anisotropy to exist
`
`‘if
`
`the
`
`anisotropy energy density
`
`function only contains
`
`a
`
`single maximum and a
`
`single.
`
`minimum as the magnetization angle, 9,
`
`is rotated by 180
`
`20
`
`degrees from a physical axis. Likewise we define an “ideal
`
`uniaxial" anisotropy energy to exist if the energy equation
`
`has only a
`
`sin2(e) or cos2(9)dependence. Materials and
`
`device processing to achieve a desired orientation or
`
`anisotropy is commonly difficult and sometimes impossible,
`
`25
`
`perhaps because heretofore the mechanism for achieving
`
`anisotropic orientation has
`
`not
`
`been well understood.
`
`Furthermore,
`
`uniform control of
`
`the orientation of
`
`the
`
`magnetic anisotropy is often difficult
`
`to achieve and
`
`maintain in a manufacturing process where many different
`
`30
`
`desired
`
`material
`
`properties
`
`‘must
`
`be
`
`obtained
`
`simultaneously.
`
`Background for Oriented Soft Magnetic Films
`
`35
`
`f
`
`In. magnetic devices,
`
`for example,
`
`such as _sensors,
`
`transducers,
`
`transformers,
`
`inductors,
`
`signal mixers,
`
`flux
`
`concentrators,
`
`recording media keepers, data recording and
`
`playback
`
`transducers
`
`it
`
`is
`
`common
`
`that
`
`the magnetic
`
`TDK Corporation
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`Exhibit 1002
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`TDK Corporation Exhibit 1002 Page 2
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`

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`W0 03/021579
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`PCT/US02/27327
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`response to a driving field possess high sensitivity and at
`
`the same time,
`
`low coercivity (Hc). Or stated simply,
`
`the
`
`material possesses essentially non-hysteretic behavior.
`
`For this type of behavior the device is constructed so that
`
`the applied field is directed along the hard magnetic axis
`in the
`
`results
`This
`a uniaxial magnetic material.
`of
`minimization of coercivity and hysteric effects, which are
`
`many times associated with magnetic domain wall motion of
`a material,
`
`materialsthat are multi—axial. For
`
`example,
`
`which has bi—axial anisotropy, will have two easy and two
`
`hard magnetic axes and will exhibit hystersis and losses.
`
`In. many of
`
`these applications a linear, or near
`
`linear
`
`response is also advantageous, while in other applications,
`
`such as signal mixers,
`
`a controlled non—linear response is
`
`desire.
`
`To obtain a
`
`linear‘ magnetic response,
`
`requires
`
`both applying a field along—the magnetic hard axis and that
`
`the
`
`anisotropy
`
`energy density
`
`function
`
`not
`
`only
`
`be
`
`uniaxial, but that it also have simple sin2(e) or negative
`
`10
`
`15
`
`20
`
`Since
`
`is the angle measured between
`cos2(e) dependence, where, Q,
`and
`the physically
`the magnetization vector direction
`there
`is
`the
`
`determined magnetic
`
`easy
`
`axis.
`
`mathematical
`
`identity,
`
`sin2(eh= 1- cos2(e),
`
`and since the
`
`origin in the energy function is arbitrarily defined the
`
`25
`
`use
`
`of
`
`behavior.
`
`or
`sin2(e)
`Item [1]
`
`-cos2(e)
`
`yield
`
`equivalent physical
`
`of Figure 1
`
`illustrates the squared
`
`sinusoidal anisotropy energy density curve shape versus the
`angle of the magnetization vector with respect
`to the easy
`
`axis located at zero degrees.
`
`Figure 2
`
`illustrates the
`
`response of
`
`the components of the magnetization, Mx and My,
`
`30
`
`as a
`
`function of applied field,
`
`Hx = Ha, along the hard
`
`magnetic axis direction, x. The linear curve kinks only at
`the point
`[2] where the magnetization becomes saturated, or
`fully aligned with the applied field. For
`this special
`
`uniaxial anisotropy this occurs at the applied field value
`
`35
`
`of
`
`Hk
`
`along the
`
`x direction, which
`
`is
`
`known
`
`as
`
`the
`
`anisotropy field.
`
`These
`
`response curves are sometimes
`
`referred to as hysteresis loops even though they exhibit no
`
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`W0 03/021579
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`PCT/US02/27327
`
`hystersis.
`
`It
`
`is the shape of
`
`the sin2(e) energy function
`
`that causes the response, Mx, along the hard axis to be
`
`linear and to be fully reversible.
`
`My is the response in
`
`the y direction to an applied field in the x direction.
`The
`
`shown
`
`is
`
`quadratic
`
`for applied field
`
`curve
`
`shape
`
`magnitudes
`
`less
`
`than Hk,
`
`where My
`
`is
`
`zero for
`
`larger
`
`magnitude fields.
`
`The quadratic behavior is necessary for
`
`linear Mx
`constant,
`
`is
`where Ms
`=
`since Nu:
`the total,
`wt‘+M,2,
`saturation magnetization vector nmgnitude.
`If
`
`10
`
`the anisotropy energy is uniaxial, but
`
`is not governed by
`
`the,
`
`ideal,
`
`sin2(e)
`
`functional
`
`form then the magnetic
`
`response is not linear. However, heretofore,
`
`the applicant
`
`knows of
`
`no
`
`real material
`
`examples exhibiting both a
`
`15
`
`uniaxial
`behavior.
`
`energy curve
`
`and ya non-linear Mx versus
`
`Hx
`
`Materials
`
`exhibiting
`
`the
`
`sin2(e)
`
`energy
`
`density
`
`functional
`
`forni are often, referred to as having Stoner-
`
`ideal uniaxial single
`Wohlfarth behavior after the famous
`However,
`thin films are
`domain magnetization theory.
`
`20
`
`25
`
`30
`
`35
`
`the
`commonly nmlti—domain even though they might exhibit
`localized basis.
`
`sin2(9)
`
`functional
`
`energy _form on
`
`a
`
`Unless the hard axis direction is the same at all points in
`
`a sample and the applied driving field is exactly parallel
`to the hard axis then domain wall motion can commonly be
`observed. This motion results in coercivity mechanisms and
`
`hysteretic energy losses.
`
`represented by Figure
`
`2
`
`The lossless behavior of samples
`the
`
`is
`
`due
`
`to
`
`magnetization
`
`rotating in response to the applied field rather than a
`
`response via domain wall motion. Multi—axis
`
`anisotropy
`
`materials
`losses.
`
`always
`
`switch via wall motion and
`
`so suffer
`
`It
`
`is also well known that,
`
`for soft uniaxial
`
`thin
`
`films, by first applying a field along the easy axis, and
`
`then by keeping a constant bias field in this direction,
`
`to
`
`eliminate 180 degree domain walls, one can force all of the
`
`material to appear to be single domain as the hard axis is
`Hence ,
`
`because of this bias field, Hb = Hy,
`
`in
`
`then driven.
`
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`Exhibit 1002
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`TDK Corporation Exhibit 1002 Page 4
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`

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`W0 03/021579
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`PCT/US02/2 7327
`
`the easy axis direction the application of any finite Hx
`
`field along the hard axis
`
`can never
`
`quite drive the
`
`magnetization vector completely to the energy maximum [3]
`
`and the response will always be reversible and so lossless.
`
`This is not the case for materials with multiple anisotropy
`
`axes. For uniaxial materials the rotational response is key
`
`to many sensor devices and it is common in various forms of
`
`magnetoresistive sensors to provide a bias field along the
`
`easy axis.by either applying a small field or by exchange
`
`coupling the magnetic sensor material
`
`to a hard magnetic
`
`material that has been so oriented to provide an effective
`
`bias field.
`For
`some
`
`sensor applications,
`
`such
`
`as
`
`anti—theft
`
`.devices,
`
`and special electronic mixing circuit devices,
`
`soft,
`
`low
`
`loss,
`
`magnetic
`
`properties
`
`are
`
`desired
`
`simultaneously with a specific non—linear
`
`response.
`
`In
`
`the driving field has historically, and
`these applications,
`most commonly, been directed along an easy axis or in the
`
`direction of
`
`the lowest magnetic anisotropy' energy.
`
`In
`
`this direction magnetic
`
`domain wall motion is usually
`
`significant. This domain wall motion commonly results in a
`
`highly non—linear
`behavior.
`
`response or even in strong hysteretic
`
`Certain anti-theft,
`
`article
`
`surveillance,
`
`article
`
`identification or
`
`inventory control devices
`
`rely upon
`
`detecting harmonic signals, which are generated by this
`
`non—linear behavior or upon materials being driven in to
`
`saturation.
`
`One
`
`of many
`
`examples,
`
`of
`
`this
`
`type
`
`of
`
`surveillance system and tag is described in U.S. Patent No.
`
`3,747,086.
`
`This
`
`type
`
`of
`
`tag response
`
`has
`
`also been
`
`disclosed as enabling multiple bits of
`
`information to
`
`identify objects in U. S. Patent No. 5,538,803
`
`Other
`
`article tag ‘devices
`
`are based upon
`
`the magnetoelastic
`
`effect
`
`and mechanical
`
`resonance, where
`
`coupling exist
`
`between the magnetization and the mechanical strain in the
`
`material. An example, of this type of tag is disclosed in
`In these later devices it is
`U.S. Patent No. 4,510,489.
`
`desirable to drive the magnetization towards a hard axis so
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
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`TDK Corporation
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`Exhibit 1002
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`Page 5
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`TDK Corporation Exhibit 1002 Page 5
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`W0 03/021579
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`
`that rotation of
`
`the magnetization dominates and magnetic
`
`hysteretic losses are minimized.
`
`By using this mode, and
`
`by using the field to drive the device at
`
`its mechanical
`
`resonance frequency significant amounts of energy can be
`stored in the device.
`Hence, even after the drive field
`
`has been removed the mechanical vibration continues,
`
`the
`
`magnetoelastic properties
`
`are then used to invert
`
`the
`
`process
`
`to transmit
`
`a magnetic field as
`
`the mechanical
`
`stress
`
`causes
`
`the magnetization vector direction to
`
`10
`
`15
`
`20
`
`rotationally oscillate synchronously with the mechanical
`vibration.
`
`This time dependent magnetic dipole radiates a
`which
`
`magnetic field at the distinct resonance frequency,
`Uniaxial
`
`can be detected to verify the tag’s existence.
`.
`such a device to achieve _low
`anisotropy is needed in
`
`losses.
`
`Due
`
`to the uagnetoelastic coupling between the
`
`mechanical strain and the magnetic moment orientation the
`mechanical
`resonance
`
`fundamental
`
`of
`
`the
`
`frequency
`
`is
`
`emitted as an oscillating magnetic dipole field. However,
`
`is non—idea1 and results in a
`if the uniaxial anisotropy
`then the
`
`non-linear
`
`response
`
`harmonics would also be
`
`available for detection in the presence of a drive signal.
`
`there have never been available
`This is advantageous, but
`materials from which to form such a device before.
`
`25
`
`Likewise,
`in analog mixer circuit devices a non-linear
`response is desired. When two separate sinusoidal signals
`
`are simultaneously imposed on a nonlinear circuit device
`
`30
`
`35
`
`component a multiplication process results in a beating of
`the two signals.
`This results in additional harmonics at
`the sum and difference frequencies of the initial signals.
`information contained
`
`Hence,
`
`the
`
`in a modulated carrier
`shifted to
`
`a beat
`
`frequency.
`
`frequency signal
`
`can be
`
`Typically this is done to shift
`bandwidth
`to
`a
`
`higher
`
`carrier
`
`the information carrying
`bandwidth
`
`frequency
`
`(modulation)
`
`or bring the information carrying bandwidth
`
`signal back down to a bandwidth located near, or nearer to,
`These
`
`zero
`
`frequency
`
`for
`
`demodulation.
`techniques
`of
`common
`to telecommunication and
`
`frequency shifting are
`
`signal processing and in many other
`
`signal processing
`
`TDK Corporation
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`Exhibit 1002
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`Page 6
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`TDK Corporation Exhibit 1002 Page 6
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`applications.
`
`The
`
`non-linear circuit
`
`response,
`
`circuit
`
`components,
`
`and circuit
`
`implementation used to perform
`
`these
`
`signal mixing processes
`
`are described in many
`
`electrical engineering circuit textbooks. Two example texts’
`
`are “Electronic Communications-Techniques"
`
`by P.
`
`H. Young
`
`and
`
`“Physics of Semiconductor Devices”
`
`by S. M.
`
`Sze.
`
`Ideally the non-linear device used to mix the signals is
`
`efficient,
`
`low loss,
`
`and low noise.
`
`Usually non-linear
`
`Silicon active devices are used for this.
`
`In the past when
`
`10
`
`magnetic devices were used for this application domain wall
`
`motion caused both losses to the signal and induced noise.
`
`A magnetic material with non-linear response that operates
`by low loss magnetization rotation rather than by domain
`
`15
`
`_
`wall motion is very desirable.
`For most all transducer and sensor applications, which
`
`require low anisotropy values inzorder to provide large
`
`sensitivityy the use ‘of cubic crystalline materials. are
`fold
`common.
`However,
`due
`to the
`three
`crystalline
`
`symmetry’ of cubic materials,
`
`achieving a single axis of
`
`20
`
`25
`
`30
`
`35
`
`anisotropy energy density, which is almost always essential
`to obtaining the desired low loss,‘ low noise, magnetic
`is difficult.
`Thin, or thick,
`
`film materials
`
`properties,
`
`are commonly employed.
`data
`
`field transducers,
`storage playback transducers or
`fcc,
`face
`centered
`cubic,
`thin film
`
`commonly utilize
`
`For example many devices,
`
`such as
`
`Should these materials be prepared
`
`crystalline materials.
`with a
`
`(001) crystalline texture the anisotropy energy, as
`
`a function of angle
`
`in the filwl plane is bi—axial, has
`
`multiple easy and hard axes in the film plane yielding a
`
`non-linear
`
`and. hysteretic magnetic response resulting in
`
`signals.
`noisy
`desired,
`
`(111)
`
`Hence,
`a
`crystalline texture is
`where it can be mathematically shown for the case
`texture
`
`of
`
`the nagnetization being confined to the (111)
`
`plane,
`
`that due to the crystalline three fold symmetry of
`
`the projection of the {111} crystalline directions into the
`
`film plane,
`
`the cubic material will possess no net first
`
`order anisotropy‘ energy density. Even for only moderate
`
`saturation magnetization thin films,
`
`the magnetization is
`
`TDKComomfion
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`PCT/US02/27327
`
`essentially
`
`confined
`
`to _
`
`the
`
`film plane
`
`by
`
`the
`
`demagnetization forces associated with the planar
`
`film
`
`shape.
`
`To achieve a single ‘uniaxial anisotropy'
`
`in a cubic
`
`material with
`
`(111)
`
`texture
`
`the material
`
`is usually
`
`subjected to a thermal treatment, or is deposited directly,
`
`in the presence of
`
`an
`
`applied magnetic
`
`field.
`
`The
`
`resulting single magnetic easy axis is aligned along the
`field,
`while
`the
`hard
`
`axis
`
`is
`
`applied magnetic
`
`10
`
`perpendicular
`
`to this applied field. Furthermore the Mx
`While
`
`versus Hx response function is a linear response.
`the mechanism for
`the
`cause
`of
`this
`
`induced magnetic
`
`anisotropy is not well understood it is often argued that
`to break the
`an atomic
`
`15
`
`symmetry of
`
`grain of the material.
`
`pair ordering mechanism occurs
`(111)
`the directions in the
`plane for each
`on a local scale inside
`That
`is,
`
`each grain,
`
`pairs of atoms align along the applied field
`during the deposition, or the annealing process,
`to reduce
`
`Interestingly, annealing in a
`the magnetic field energy.
`field of different orientation can often alter this induced
`
`20
`
`the orientation
`anisotropy direction demonstrating that
`It is believed that this
`
`inducing mechanism is reversible.
`
`localized ordering allows fcc materials such as the NiFe
`
`alloys,
`
`permalloy,
`
`to have
`
`a
`
`small
`
`induced uniaxial
`
`anisotropy.
`
`Magnetic thin film body centered cubic, bcc,
`FeCo, FeAl,
`and
`or bcc derivative materials,
`such as Fe,
`
`similar compositions,
`
`because
`
`the
`
`required
`
`are seldom used in such applications
`texture
`(111)
`
`crystalline
`
`never
`
`develops during deposition of the bcc symmetric crystals.
`
`It
`
`is well understood that during the growth of thin
`
`metal
`
`films certain texture orientations tend to appear.
`
`These are driven by the minimization of surface energy and
`
`25
`
`30
`
`surface bonding considerations and are modified by surface
`which
`
`can
`
`be
`
`somewhat
`
`controlled by
`
`mobility issues,
`
`.35
`
`substrate and processing conditions. One
`
`simple rule of
`
`thumb is that the film surface energy is minimized when the
`
`atomic surface configuration is the most closely packed.
`
`For a fcc crystal the atoms in the surface are most closely
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`
`packed in the (111) plane and so this texture is the most
`
`likely.
`The
`(001)
`texture is less energetically likely,
`but
`is possible where as
`the high surface energy (110)
`texture never seems to occur.
`On the other hand, for a bcc
`
`crystal the atomic surface most closely packed is the (110)
`
`texture and this commonly appears,
`
`the (001)
`
`texture is the
`
`next
`
`the high
`lowest energy and is sometimes induced, but
`texture never seems to occur. Hence,
`
`surf ace energy (1 1 1)
`
`for fcc crystals we refer to the
`
`(111)
`
`texture as being
`
`10
`
`natural where as for the bcc crystal we refer to the (110)
`
`texture as being naturally occurring.
`
`If a low surface
`
`energy substrate
`which 'tends
`
`to wet
`
`is chosen,
`
`to the depositing’ material,
`
`such as an amorphous metal,
`the fcc
`
`15
`
`texture naturally occur. On
`texture and the bcc (110)
`(111)
`the other hand,
`if the substrate is non—wetting, such as an
`
`oxidized surface where
`bond to the
`
`the depositing material
`to limit
`the
`
`tends
`
`to
`
`oxygen atoms
`atomic
`surface
`then it is_common to see limited orientation in
`
`mobility,
`
`20
`
`25
`
`30
`
`35
`
`the deposited films or at best a set of mixed textures.
`The
`fcc
`(111)
`and
`
`crystal
`
`tends
`
`to
`
`form only weak
`
`(O01)textures while the bcc crystal tends to form only weak
`
`(110) and (001)
`
`textures.
`
`thin film grains with (110) or
`
`(001)
`
`For magnetic cubic crystalline
`texture there are
`
`multiple easy or hard axes in the film plane of the grain.
`
`In addition,
`because
`each grain has a- random in-plane
`orientation relative to other grains,
`these polycrystalline
`magnetic materials result
`in an ensemble of grains with
`
`multiple,
`
`random, anisotropy axes.
`
`These materials yield
`
`both. a non—linear
`
`response,
`
`as well as, high coercivity
`
`associated with losses
`
`and noise.
`
`Hence,
`
`bcc or bcc
`
`derivative materials, which almost always grow with (110)
`
`or
`
`(001)
`
`texture, are seldom used for devices.
`
`For
`
`this
`
`reason the high
`have
`
`materials
`
`saturation magnetization value of bcc
`device
`
`largely been unavailable to the
`
`designer who wishes to avoid domain wall motion.
`
`One need only consult
`
`the very authoritative text,
`
`“Physics
`
`of
`
`Ferromagnetism,
`
`2nd Edition”
`
`by
`
`Soshin
`
`Chikazumi,
`
`pages 299-309, on thermally induced anisotropy
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`
`of permalloy to see that the degree of understanding of the
`
`cause of uniaxial anisotropy in cubic materials is poor.
`
`Professor Chikazumi details the literature on the subject
`that
`thi S
`and notes
`one
`theory attempts
`to explain
`terms
`of
`“directional
`“phenomena
`order,”
`or
`
`in
`
`an
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`anisotropic distribution of different atomic pairs such as
`Ni—Ni,
`Fe—Fe,
`
`The
`
`logic is that
`
`the atomic
`
`or Ni—FeJ'
`
`spacing between the Ni—Fe pair is smaller than the other
`
`possible pairs and so a lattice distortion results from the
`
`atomic pairing. A nwgneto-crystalline uniaxial anisotropy
`
`is then proposed to result from the magneto-elastic energy
`with
`the
`
`associated
`
`resulting
`
`lattice
`
`distortion.
`
`Professor Chiakazumi also outlines a second theory in which
`
`it
`
`is “assumed.
`
`that ordering occurred by the growth. of
`
`distinct volumes of
`
`the ordered phase,
`
`and explains the
`
`induced anisotropy as the result of shape anisotropy of the
`
`Geometrical grain shapes,
`second phase."
`spherical,
`could generate considerable shape
`
`than
`other
`anisotropy
`
`energy.
`
`It should be pointed out however,
`
`that no physical
`
`evidence
`
`supporting either of
`
`these theories has been
`
`provided.
`
`Shape
`
`explanation,
`
`anisotropy is
`this
`
`as
`
`an
`
`intellectually comforting
`
`phenomenon is quite observable in
`
`elongated magnetic
`
`particles
`
`such as used in magnetic
`
`particulate data storage tapes and bar
`
`shaped permanent
`
`magnets.
`
`In these,
`
`the magnetic easy axis is aligned with
`
`the longer dimension. However, while Professor Chiakazumi
`
`illustrates that a rather complex pair ordering model with
`
`dipole-dipole interactions proposed by Neel can be used to
`
`qualitatively explain field induced anisotropy,
`
`there is no
`
`quantitative agreement
`
`and. he comments
`
`“The
`
`reasons why
`
`quantitative agreement
`
`is not obtained may
`
`lie in the
`
`approximate estimates of various quantities'and in failure
`
`to attain complete thermal equilibrium.”
`the
`the
`
`comments
`
`regarding
`
`texture
`
`of
`
`Nevertheless, he
`that
`
`materials
`
`“magnetic annealing is most effective for,
`<111> annealing,
`and least effective for <100>."
`less effective for <110>,
`
`In
`
`this
`
`statement
`
`he
`
`is
`
`referring to
`
`the
`
`parallel
`
`l0
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`
`orientation of
`
`the
`
`applied field and
`
`the
`
`crystalline
`
`directions during the annealing process.
`
`"Soft High Saturation
`Very recently a publication;
`(Fem7Com3)L*Nx Thin Films For Inductive Write
`
`Magnetization
`
`Heads,"
`
`IEEE ‘Transactions
`
`(hi Magnetics,
`
`Vol. 36, No. 5,
`
`September 2000, by N. X. Sun and S. X. Wang,
`
`claimed to
`
`achieve orientation of
`
`the
`
`bcc
`
`like material
`
`during
`
`deposition in an applied magnetic field. The publication
`
`10
`
`to
`appears
`necessary,
`
`the Nitrogen
`that
`indicate
`induced strain into the films,
`
`was
`content
`and created a
`
`small grain structure as
`broadened,
`the (110)
`that
`a
`indicated
`
`it shifted the angle of,
`
`and
`
`They also
`a
`second
`
`x-ray diffraction peak.
`“significant
`amount”
`of
`Fe4N-,
`
`15
`
`20
`
`25
`
`30
`
`35
`
`crystalline magnetic phase,
`
`appeared in the films. As
`
`Chikazumi suggests perhaps this anisotropy behavior is due
`
`to the strain or shape or pair ordering associated with the
`
`It is interesting to note that they obtained
`second phase.
`(100)
`textured substrate
`this orientation on an oxidized Si
`
`and by the applicant's standards the FeCoN (110)
`weak.
`
`They‘ went on to indicate that by sandwiching the
`hard
`
`FeCoN film between two permalloy films
`
`the
`
`axis
`
`texture is
`
`coercivity could be decreased, but they did not indicate or
`offer any evidence that
`the orientation of
`the FeCoN film
`was improved by depositing upon the permalloy.
`In fact, a
`
`comparison of hard axis hystersis loops for films prepared
`with and without
`the
`
`permalloy films
`
`indicate similar
`
`anisotropy fields necessary to saturate the magnetization.
`This
`that
`the
`indicate
`
`permalloy layer did not
`
`would
`
`improve the orientation in their structure.
`
`Background For Orientation with Hard Magnetic Films
`
`It
`
`should be noted that unlike field sensing and
`
`energy transforming devices
`
`that usually require
`
`soft
`
`magnetic materials,
`
`devices
`
`such as magnetic
`
`recording
`
`media
`
`and
`
`permanent magnets
`
`demand
`
`higher
`
`uniaxial
`
`‘anisotropy energy in order to achieve high coercivity Hc,
`and a preferred orientation in order
`to achieve a high
`
`11
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`
`this directly
`For motors or actuators
`remnance value.
`affects the amount of work that a device can deliver while
`
`for recording media it directly affects the output signal
`level and signal pulse width, or
`flux transition width,
`Even in some of these
`
`the recording density.
`
`and, hence,
`
`hard magnet applications it
`
`is desirable to incorporate
`
`soft magnetic materials
`
`to enhance overall performance.
`
`For example, perpendicular
`
`thin film recording media has
`
`long
`
`been
`
`discussed
`
`as
`
`a
`
`future
`
`replacement
`
`for
`
`longitudinal
`
`thin film media.
`
`However,
`
`in order
`
`for
`
`a
`
`recording system to function properly it is desirable that
`a soft magnetic keeper layer, or underlayer, be placed on
`the
`the
`opposite
`side~ of
`perpendicular hard magnetic
`
`recording layer from the recording head.
`
`This soft
`
`then provides a flux return path, or flux concentrator,
`
`layer
`for
`
`the recording head fields, as well as, a flux closure path
`
`for stabilizing the recorded bits against demagnetization
`energies after the head is removed.
`The
`former enables
`
`to function with higher coercivity media
`recording heads
`and with better
`the
`
`resolution, while
`
`later provides
`
`improved stability to the recorded patterns by eliminating
`
`a portion of
`
`the self—demagnetization energy associated
`
`with. perpendicular
`soft
`
`media
`
`a
`
`magnetic
`
`recording.
`
`In longitudinal
`
`layer would
`
`also improve
`
`recording
`the
`
`10
`
`15
`
`20
`
`25
`
`stability of
`
`energy
`demagnetization
`However, heretofore,
`
`the recorded patterns by reducing the self-
`’
`the
`hard
`
`of
`
`-recording
`
`layer.
`
`no soft magnetic underlayer has been
`
`found
`
`to be
`
`a
`
`either
`for
`satisfactory keeper
`perpendicular or longitudinal media as no good method of
`
`layer
`
`30
`
`35
`
`controlled the anisotropy orientation has been available.
`
`Soft magnetic underlayers, without a uniform and controlled
`results in domain wall
`induced media
`
`anisotropy direction,
`
`noise via domain wall motion Barkhausen phenomena.
`
`As
`
`the
`
`magnetic head passes over
`
`the media data it effectively
`
`shorts out
`
`the stray media bit fringe fields causing the
`
`magnetic patterns in the soft magnetic underlayers to relax
`
`to new positions.
`If there are significatn domain walls
`involved in this process they commonly break loose from
`
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`
`localized pinning defects causing sudden changes in their
`
`magnetic configuration.
`
`This Barkhausen phenomena causes
`
`noise signals to appear
`
`in the data playback head.
`
`For
`
`either perpendicular or longitudinal hard disk recording,
`
`where the recorded bit or
`
`flux patterns have been wider
`
`across the recorded track than the bit length,
`
`the desired
`
`anisotropy configuration for the soft layer is for the hard
`magnetic axis to be along the recorded track so that
`the
`easy axis lies across the track direction.
`Hence,
`for a
`
`10
`
`15
`
`traditional hard disk systeni
`
`this implies that
`
`‘axis of
`
`the soft
`
`film should be directed radially,
`
`the easy
`while
`
`the hard axis is directed circumferentially.
`
`Since the
`
`easy axis of the soft magnetic layer of this configuration
`to the fields
`flux
`is at
`90 degrees
`produced by the
`
`transitions of the hard recording layer,
`
`the magnetization
`
`vector of the soft magnetic layer rotates by spin rotation
`
`and the noise generating domain wall motion is avoided.
`Having a uniaxial
`soft magnetic underlayer with radial
`
`20
`
`orientation will solve a long-standing technical problem.
`As
`data
`storage
`areal densities
`are
`pushed
`forward,
`
`magnetic grain sizes have been reduced to the extent
`
`that
`
`the magnetic recorded state is near the thermal stability
`
`limit.
`
`Hence,
`
`even longitudinal
`
`recording stability and
`
`the transition length also benefit
`
`25
`
`magnetic
`
`underlayer
`
`to
`
`reduce
`
`from the use of a soft
`bit
`
`the
`
`transition
`of domain wall
`
`demagnetizing effects.
`
`Again,
`
`because
`
`motion generates noise the ideal orientation of
`
`the soft
`
`underlayer easy axis
`
`should be
`
`radial
`
`to minimize
`
`the
`
`potential
`
`for domain wall noise. Similarly,
`
`anisotropy
`
`30
`
`orientation
`
`addressable
`
`control
`data
`
`by providing a keeper
`storage
`layer wherein the magnetization vector is rotated by spin
`rotation and
`domain
`wall
`motion
`is minimized.
`This
`
`can benefit magnetic
`
`tape
`
`and x—y
`
`systems
`
`invention, of oriented soft magnetic materials,
`
`represents
`
`35
`
`a significantly improving future magnetic media.
`
`Background For Hard Magnetic Film Orientation
`
`13
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`
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`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`a
`Modern hard disk longitudinal media‘ consists of
`polycrystalline thin film composed essentially of uniaxial
`
`grains randomly oriented in the substrate plane.
`
`Playback
`
`by averaging the signals from the randomly oriented grains
`
`results in an isotropic response around the disk radius.
`
`This orientation randomness has been necessary to avoid the
`twice around modulation during disk rotation of
`a non-
`isotropic media.
`By mechanically grooving the disk surface
`
`prior to deposition of
`
`the thin film layers some
`
`small
`
`amount of orientation along the circumferential direction
`
`is sometimes observed. However,
`remanence
`of
`the hard magnetic
`radial
`remanence is seldom more
`
`the orientation ratio, OR,
`along the track to the
`than 1.2 and more often
`
`typically less
`substrates have been made
`
`than
`
`1.1
`
`and
`has
`been decreasing as
`smoother and media films made
`
`thinner
`
`enable
`to
`the
`
`higher
`the
`
`areal
`
`recording densities.
`the
`
`Likewise,
`ratio ‘of
`coercivities
`in
`two
`directions is also sometimes referred to as the orientation
`
`ratio,
`
`OR,
`
`and its maximum value is also typically similar
`
`to that of
`
`the magnetic remanence ratios.
`
`The origin of
`
`this hard magnetic material orientation has been in dispute
`
`for several years. While it has been argued by some that
`
`it originates from a slight preference of the c-axis of the
`
`hexagonal close packed, hcp, cobalt alloy to lie along the
`
`grooved direction,
`the
`vanish if
`
`disk is
`
`it has also been shown to diminish or
`
`thermally cycled before media
`This latter
`
`deposition, but after the mechanical grooving.
`
`phenomenon
`
`has
`
`resulted
`
`in
`
`some
`
`arguing
`
`that
`
`the
`
`orientational origin is due to a thermal stress development
`
`between the substrate and the film layers as the substrate
`
`stress associated with the grooves relaxes from the heat
`used,
`
`or generated, during the deposition.
`Marinero et al. outlines
`5,989,674,
`
`publications
`
`orientation and
`
`claiming
`then
`
`to
`
`invokes
`
`reveal
`stress,
`
`cause
`
`of media
`
`shape
`
`and
`
`even
`
`In US Patent
`several patents and
`the
`
`crystalline orientation to clahn a cause for orientation
`
`an
`during the deposition of
`substrate.
`
`mechanically grooved
`
`cobalt
`hcp
`a
`alloy on
`Others
`had claimed to
`
`14
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`
`W0 03/021579
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`
`achieve small orientation ratios by deposition of the media
`
`materials at an oblique angle to the disk surface.
`See for
`example, U.S. Patent No. 4,776,938. While this approach has
`shown some effect it has not resulted in a significantly
`
`improved OR over grooved substrates
`methods
`
`described are
`
`significantly inefficient
`
`in the
`
`and the deposition
`
`deposition of material.
`
`origin of
`
`the crystallographic
`Eurthermore,
`this orientation effect has also never been
`
`clearly stated or proven and it is possible that it is due
`
`10
`
`to particle shape effects.
`
`In spite of it's the patent
`
`description a number of years
`
`ago the method is not a
`
`technology that is currently used in production.
`the
`Nevertheless,
`from
`wherever
`
`orientation
`
`15
`
`originates,
`
`recording
`
`it has been proven to be beneficial to magnetic
`shorter
`for
`resolution a