A Proposal to Advanced Storage Technology Consortium (ASTC)
Topic Number: MAMR No. 4
Proposal Title: Damping in Present Magnetic Recording Media
Principle Investigator: Mingzhong Wu
Department of Physics, Colorado State University, Fort Collins, CO 80523
Phone: (970) 491-6312; Fax: (970) 491-7947; E-mail: mwu@lamar.colostate.edu
Administrative Contact: Bo Bogdanski
Colorado State University Sponsored Programs, Fort Collins, CO 80523-2002
Phone: (970) 491-5574; Fax: (970) 491-6147; E-mail: bo.bogdanski@colostate.edu
Project Period: July 1, 2011 – June 30, 2012. Amount: $69,995. Submission date: April 28, 2011
Project Summary
Understanding the damping of magnetization precession in magnetic recording media is of both
fundamental and practical importance. In practical terms, the damping processes in media not only set a
natural limit to switching times and recording data rates, but also play a critical role in microwave-assisted
magnetization switching. In spite of such importance, however, the study of damping in recording media
is still rather limited.
The goal of this project is to use comprehensive ferromagnetic resonance (FMR) measurements and
numerical analyses to identify and quantify different physical relaxation processes in present recording
media. We will carry out temperature-, frequency-, and angle-dependent FMR measurements in various
media samples from the sponsors. We will not only determine the total damping constant α, but will also
separate different components in α which are responsible for different damping processes. Our work will
also yield detailed information on the temperature dependence of α, the levels of spatial inhomogeneity in
the media, and the effects of media properties on α.
The research team has extensive experience in studying damping in magnetic materials, including
recording media and head materials from the magnetic recording industry, and also in studying
microwave-assisted magnetization reversal. These studies were carried out through close collaborations
with scientists in the industry and were supported in part through research grants from INSIC, Western
Digital, and Seagate.
1
I. Background
a. A Big Picture about Damping
This section provides an overview of the damping processes in magnetic materials. It serves to
simplify the discussions in the following sections.
The magnetization in a magnetic material can precess around the direction of a static magnetic field.
One can maintain a uniform magnetization precession by the use of an RF magnetic field. Once the RF
field is turned off, however, the magnetization will tend to relax back to the static field direction. Figure 1
gives a schematic roadmap for the relaxation (or damping) of uniform magnetization precession. The
arrows and numbers indicate different relaxation routes.
Generally speaking, there are three main
pathways for magnetization relaxation in a magnetic material [1,2,3,4,5,6]:
(I) Energy redistribution within the magnetic system through routes 2 and 3;
(II) Energy transfer out of the magnetic system to non-magnetic systems through routes 1 and 4;
(III) Energy transfer out of the material to external systems through route 5.
Possible physical relaxation processes in routes 1-5 are summarized in Table I. The relaxation
processes in routes 6 and 8 are similar to those in route 1, and the processes in route 7 are similar to
those in route 3.
Several phenomenological models have been proposed to describe the relaxation of the uniform
magnetization. These models include the Gilbert model (also called the LLG model), the Landau-Lifshitz
model, and the Bloch-Bloembergen model.
Each model can take into account one or more of the
relaxation processes listed in Table I. None of the existing models, however, can take into account all of
the processes. For example, the Gilbert model can rigorously describe the magnon-phonon and magnonelectron scattering processes, but fails to describe the two-magnon scattering process.
In the two-
magnon scattering process, the longitudinal component of the magnetization is unchanged, and the
length of the magnetization vector decreases. As a result, this process can only be described by the T2
term in the Bloch-Bloembergen equation. In this sense, it is incorrect if one attempts to describe all the
relaxation processes in a material with a single damping parameter, such as the Gilbert constant α.
3


5


4


1
2


6
7


8


FIG. 1. A roadmap for the relaxation of uniform magnetization precession in magnetic materials
2
Table I. Physical Relaxation Processes in Magnetic Materials
Route
Relaxation Process
Magnon-phonon
scattering
Charge transfer
relaxation
1
Slowly relaxing
impurity
Rapidly relaxing
impurity
Eddy current
2
3
Two-magnon
scattering
Three-magnon
scattering
Four-magnon
scattering
Spin-flip magnonelectron scattering
4
Breathing Fermi
surface
5
Spin pumping
Brief Description
For this process, one views the uniform precession modes as magnons with zero
wavenumbers. Those magnons scatter with phonons (lattice vibration modes)
and pass their energy to the phonons.
2+
3+
This process is also called the valence-exchange or Fe -Fe relaxation and
2+
3+
occurs in crystals with Fe and Fe ions on equivalent sites. When there is a
net spin alignment, the site degeneracy is split slightly. Via spin-orbit coupling,
the precession leads to the breathing of the energy level of each site, resulting in
the hopping of a 3d electron from one iron ion to another.
The impurities are usually rare-earth elements. The relaxation relies on the
exchange coupling between the spins of magnetic elements and those of
impurity and the coupling of the impurity spins to the lattice. The exchange
coupling is anisotropic. As a result, the splitting of the two lowest energy levels
depends on the instantaneous direction of the magnetization, leading to the
transitions of the impurity between the two energy levels.
This is similar to the slowly relaxing impurity mechanism. The difference is that
the exchange coupling is isotropic and the energy levels do not breathe. The
impurities absorb energy from the magnetization precession and changes from
the ground state to the excited state.
This involves a loss of energy of the uniform precession to the lattice through the
conduction electrons. The eddy-current damping increases with the square of
the linear sample dimension, such as the film thickness.
This process involves the scatting of zero-wavenumber magnons with
inhomogeneities, such as grain-to-grain fluctuations, grain boundaries, small
pores, and surface defects. After each scattering, the initial magnon is
annihilated and a new magnon is created. The new magnon has a frequency
which is the same as the initial magnon and a wavenumber which correlates with
the spatial variation of the inhomogeneities.
This process includes three-magnon confluence and three-magnon splitting. In
a confluence process, two magnons scatter with each other and are annihilated,
and one new magnon is created. In a splitting process, one magnon is
annihilated and two new magnons are created.
In each scattering process, two magnons scatter with each other and are
destroyed, and two new magnons are created.
When a “spin-up” free electron scatters with a magnon, it absorbs the energy of
the magnon, destroys the magnon, and changes into a “spin-down” electron.
With an increase in temperature, the electron lifetime decreases and the electron
Fermi level broadens. As a result, the magnon-electron scattering probability
increases and the damping increases.
This process is also called intraband magnon-electron scattering. Via spin-orbit
coupling, the magnetization precession changes the energy of the free electron
states, pushing some occupied states above the Fermi level and some
unoccupied states below the Fermi level. As a result, the electron-hole pairs are
produced near the Fermi level. These pairs exist for some lifetime before
relaxation through scattering with the lattice. The energy dissipated to the lattice
depends on how far the system gets from equilibrium, and the latter increases
with the electron lifetime.
At a ferromagnet/normal metal interface, the magnetization precession in the
ferromagnet produces a spin current that flows into the normal metal. This spin
current carries spin angular momentum out of the ferromagnet.
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b. Ferromagnetic Resonance
Ferromagnetic resonance (FMR) is probably the most widely used technique for the study of the
damping of uniform precession. The left diagram in Fig. 2 shows a schematic representation of the FMR
effect, where the magnetization M absorbs energy from the microwave magnetic field h and maintains a
fixed angle of precession around the static magnetic field H. The FMR effect manifests itself in a peak
response in the measurement of the
Power absorption
z
power absorption in the material as a
H
function of the static magnetic field, as
shown by the right diagram in Fig. 2.
M
This peak response is, more or less,
Lorentzian in shape. The full width at
the half maximum of this so-called
h
x
y
FMR absorption curve is usually taken
∆HFMR
HFMR
Static magnetic field H
FIG. 2. Schematic of ferromagnetic resonance (FMR)
as the FMR linewidth ∆HFMR.
The origin of the FMR linewidth differs significantly in different materials. In general, one can express
the linewidth as
∆H FMR =  ∆H i + ∆H 0
(1)
i
where ∆Hi denotes the contribution from a certain relaxation process i and ∆H0 takes into account the
inhomogeneity-caused line broadening.
It is important to emphasize that the inhomogeneity line
broadening is not a loss. It arises from the simple superposition of several local FMR profiles for different
regions of the sample. Those local FMR profiles are shifted in field because of some change in the
magnetic properties of the different regions.
At the first glance, it might seem difficult to obtain useful information on damping from ∆HFMR
measurements, since the linewidth ∆HFMR consists of many terms. In practice, however, FMR techniques
have proved to be an extremely useful tool for the identification and even quantification of different
physical damping processes in a great variety of materials. This is possible due to three facts as follows.
(1) For a specific material, not all the processes listed in Table I are involved in the relaxation. Rather,
only a few of the processes take place or play important roles. In a high-resistivity ferrite, for example, the
relaxation via the magnon-phonon scattering and charge transfer processes are possible, but the eddy
current and magnon-electron scattering effects are negligible. (2) Many of the relaxation processes show
unique temperature or frequency dependences. In some cases, this makes it fairly easy to distinguish
one process from another. (3) Some of the processes can be easily turned on or off through a change in
FMR configurations, such as the direction and magnitude of the static field. For magnetic thin films, for
example, one can suppress the two-magnon scattering simply by applying the static field normal to the
film plane.
c. Possible Damping Processes in Recording Media
Understanding the damping of magnetization precession in real magnetic recording media is of both
fundamental and practical importance. In practical terms, the relaxation processes in media not only set
a natural limit to switching times and recording data rates, but also play a critical role in microwave-
4
assisted magnetization switching [7]. In spite of such importance, however, studies on the damping in
magnetic recording media materials are still rather limited. The only work reported to date was done on
granular Co-Cr films by Professor Carl Patton’s group [8]. The work showed that, when the magnetic field
was applied perpendicular to the film plane, the only important process was the magnon-electron
scattering, which could be characterized by a small damping constant of α=0.004. It also showed that,
when the field was applied in a direction away from the film normal, there was also a grain-to-grain twomagnon scattering process, which played a more significant role in the relaxation than the magnonelectron scattering. The granular films studied in this work, however, differ significantly from real media
materials. First, the films were “soft”, with a net perpendicular anisotropy field of only 0.61 kOe. Second,
the films consisted of only a single magnetic layer, while the present media consists of a relatively
complex structure, such as the so-called ECC (exchange coupled composite) structure.
What are actual physical damping processes in the present media? Table II shows the possibility for
each relaxation process listed in Table I to contribute to the damping of magnetization precession in
media materials. The justifications were based mainly on the mechanism of each process (see Table I)
and our very recent study on the damping in a commercial-like perpendicular media disk provided by
Western Digital [9].
Table II. Possibilities for Occurrences of Different Relaxation Processes in Recording Media
Relaxation Process
Possibility
Justification
Magnon-phonon scattering
Yes
This process takes place in almost all magnetic materials.
Charge transfer relaxation
No
This process exists in ferrites, not metals.
Slowly relaxing impurity
No
There are no rare-earth elements in media materials.
Rapidly relaxing impurity
No
There are no rare-earth elements in media materials.
Eddy current
No
The eddy current damping is negligible in very thin films.
Two-magnon scattering
Maybe
This depends on the field/film configuration.
Three-magnon scattering
Maybe
This depends on the field/film configuration.
Four-magnon scattering
Maybe
This depends on the field/film configuration.
Spin-flip magnon-electron scattering
Yes
This process takes place in materials with free electrons.
Breathing Fermi surface
Yes
This process takes place in materials with free electrons.
Spin pumping
No
This effect occurs in the presence of a neighboring normal
metal.
As shown in Table II, there are six processes that might contribute to the damping in a media material.
One, however, can narrow down them to two processes only with the two considerations as follows. (1)
The occurrence of the two-, three-, and four-magnon scattering processes relies on the availability of
degenerate spin-wave modes. One can suppress the number of the degenerate modes and, thereby,
exclude these magnon scattering processes by conducting FMR measurements with a static magnetic
field perpendicular to the film (or disk) plane. (2) In metallic materials, the contributions of the magnon-
5
electron scattering and breathing Fermi surface mechanisms to the relaxation are much larger than the
contribution from the magnon-phonon scattering. As a result, it is appropriate to ignore the contribution
from the magnon-phonon scattering. With these considerations, one can take into account only the spinflip magnon-electron scattering (MES) and breathing Fermi surface (BFS) mechanisms. Therefore, for
perpendicular FMR on recording media, the linewidth can be expressed as
(2)
∆ H FMR = ∆ H MES + ∆ H BFS + ∆ H 0
where ∆HMES and ∆HBFS describe the contributions from the MES and BFS processes, respectively.
d. Damping Constant α
It is known that both the spin-flip magnon-electron scattering and breathing Fermi surface
mechanisms can be described by the Gilbert model, which is also called the LLG model. As a result, one
can rewrite Equation (2) as
∆H FMR =
2α MES
γ
ωFMR +
2α BFS
γ
ωFMR + ∆H 0
(3)
where ωFMR is the FMR frequency and γ is the absolute value of the gyromagnetic ratio. αMES and αBFS
are the damping constants responsible for the MES and BFS processes, respectively, and can be
expressed as [10]
α MES
1  T 
=A
γ M s  300 
2
 300 
 T 


2
α BFS = B
1
γ Ms
(4)
(5)
where Ms is the saturation magnetization, T is temperature (K), and A and B are two constants with the
unit of frequency. The summation of αMES and αBFS yields an overall damping constant α, which is the
very damping parameter appearing in the Gilbert equation (or the LLG equation).
II. Proposed Research
This section provides essentials for the proposed research project.
research approaches and planned works.
Subsections b-e describes
Subsection f lists the likely outcomes of the project.
Subsection g gives the time line of the project.
a. Objectives of This Project
The goal of this project is to use comprehensive FMR measurements and numerical analyses to
identify and quantify relaxation processes and determine the damping constant α in present magnetic
recording media provided by the magnetic recording industry.
b. Approaches for Damping Constant Determination
We will use two approaches to determine the damping constant of the media materials. The results
from the two approaches will be compared. Such comparison will allow us to confirm and refine each
approach and, thereby, to obtain highly-reliable damping constants.
6
As discussed in Section I.c, the dominant damping mechanisms in perpendicular recording media
are the spin-flip magnon-electron
electron scattering (MES) and breathing Fermi surface (BFS) processes. These
processes show opposite temperature dependences, as can be seen in Equations (4) and (5). The
inhomogeneity line broadening ∆H0 can be evaluated as [11]
∂H FMR  ∆H u 
∆H 0 =

 Hu
∂H u  H u 
(6)
where Hu is the effective perpendicular anisotropy field and the ratio ∆Hu/Hu describes the level of the
spatial variation in Hu. Note that the derivative term essentially equals to one for perpendicular FMR
measurements; the ratio is independent of temperature
temperature; and the dependence of Hu on temperature
temp
can
be measured experimentally.
For this reason
reason,, one can determine the damping constant through
temperature-dependent
dependent FMR measurements and the fitting of FMR linewidth data with the following
equation
∆H FMR (T ) =
2
2
2ωFMR 
1  T   2ωFMR 
1  300    ∆H u
+
B
A


+
γ  γ M s  300  
γ  γ M s  T    H u

 Hu

(7)
The equation is obtained simply by substituting Equations (4)
(4)-(6)
(6) into Equation (3). One can see that
there are three fitting parameters: A
A, B, and ∆Hu/Hu.
It is known that the value of ∆H0 is independent of frequency [12]. For this reason, one can also
rewrite Equation (3) as
∆H FMR (ω ) =
2 (α MES + α BFS )
γ
ω + ∆H 0
or
∆H FMR (ω ) =
2α
γ
ω + ∆H 0
(8)
This equation suggests another approach, namely, that one can obtain the damping constant through
frequency-dependent
dependent FMR measurements and the fitting o
off the FMR linewidth with Equation (8). In this
case, one has two fitting parameters: α and ∆H0.
c. Damping Determination through Temperature
Temperature-Dependent Measurements
This approach involves the following steps. The fitting of ∆HFMR(T) with three models is illustrated in
Fig. 3.
(1) Measure the saturation magnetization Ms of the
sample over a wide temperature range (for example,
T=100K-400K);
(2) Performance field-swept
swept FMR measurements over
the same temperature range;
(3) Determine the FMR field HFMR values from the FMR
data;
(4) Calculate the anisotropy field Hu values with the
Kittel equation and the Ms and HFMR data;
(5) Determine the FMR linewidth ∆HFMR values from the
FMR data;
(6) Fit the ∆HFMR vs. T response with Equation (7) and
obtain fitting parameters A,, B, and ∆Hu/Hu;
FIG. 3. Fitting of temperature-dependent
temperature
FMR linewidth data with three contributions:
magnon-electron
electron scattering linewidth ∆HMES,
breathing Fermi surface linewidth ∆HBFS, and
inhomogeneity line broadening ∆H0.
7
(7) Calculate the damping constants with Equations (4) and (5).
There are five important points to be noted. (1) The FMR measurements should be done with a
magnetic field perpendicular to the film plane so that the magnon-magnon
magnon scattering processes are
prohibited, as discussed in Section I.c
I.c. (2) This approach will yield the values of αMES, αBFS, and α as a
function of T,, although we are mainly interested in the values at room temperature. (3) This approach
allows us to determine not only the value of α, but also the weights of αMES and αBFS in α. (4) The work
will also yield the ratio ∆Hu/Hu. This ratio describes the level of anisotropy field fluctuation in the media
and, thereby, is of great interest to our industry collaborators who make recording media. In the case that
our collaborators can provide this ratio, the fitting parameters wil
will be reduced from three to two. (5) In
certain media materials, the inhomogeneity might consist of spatial variations in both the strength of
anisotropy field and the anisotropy axis. This will be considered in numerical analyses.
It is important to mention
ntion that, w
with this approach, we have recently succeed in determining the
values of αMES, αBFS, and α in a commercial
commercial-like
like perpendicular ECC media disk provided by Western
Digital [9]. This previous experience will greatly help the implementation of this new project.
d. Damping Determination through Frequency
Frequency-Dependent Measurements
This approach involves three steps
steps: (1) Run field-swept
FMR measurements at different frequencies
frequencies; (2) Determine
the FMR linewidth ∆HFMR values from the FMR data; and (3)
Fit the ∆HFMR vs. ω response with Equation ((8) and obtain
fitting parameters α and ∆H0 (or ∆Hu/Hu).
The fitting of
∆HFMR(ω) is illustrated in Fig. 4. We will compare the results
from this approach with those obtained with the first
approach.
This
his will allow us to refine our numerical
analyses.
We want to mention that we have previous experiences
with
frequency-dependent
dependent
FMR
measurements
FIG. 4. Linear fit to frequency-dependent
frequency
FMR linewidth data.
and
(a)
(b)
150
Cr
700
600
Ta
500
Ti
400
Cu
300
Pt
100
Inhomogeneity
line broadening
75
50
Intrinsic damping
25
200
100
12
Grain-boundary
two-magnon scattering
125
FMR linewidth (Oe)
FMR linewidth (Oe)
800
Ru
13
14
15
16
Frequency (GHz)
0
17
18
8
10
12
14
16
Frequency (GHz)
18
20
Grain-grain twomagnon scattering
FIG. 5. (a) FMR linewidth as a function of frequency for Fe65Co35 films on different seed layers, as indicated. (b)
Experimental (circles) and theoretical (solid curve) FMR linewidths for a Fe65Co35 film on a Ru seed layer. The
dashed curves in (b) show four contributio
contributions to the overall linewidth. (unpublished)
8
numerical analyses in a number of different sets of materials, including those thin film materials from
Seagate [13] and Western Digital [14]. We believe those experiences will be valuable for the work
proposed here.
Figure 5 shows representative frequency-dependent FMR linewidth data and
corresponding numerical results [13]. Note that the FMR measurements were done with an in-plane field
and, therefore, the FMR linewidth contains substantial contributions from two-magnon scattering
processes.
e. Other Work
We plan to study the effects of various media parameters and properties on the relaxation processes
and the damping constant. These parameters and properties include film thickness, grain size, and the
strength of the “granular layer” to “capping layer” coupling.
This work will be done through close
collaborations with our industry partners. We will also study the damping properties in media materials
where the damping might involve other relaxation processes (other than the magnon-electron scattering
and breathing Fermi surface processes considered above). For example, for materials with nonmagnetic
metallic layers, one might need to consider the spin pumping effect; for materials containing rare-earth
elements, one might need to take into account the slow relaxing impurity process.
For the FMR
measurements proposed above, the magnetic field will be applied along the film normal direction. Work
is also planned to use polar-angle-dependent FMR measurements to study magnon-magnon scattering
processes in certain media materials.
f. Outcomes of Proposed Project
The likely outcomes from the above-proposed work include the following:
(1) Damping constant α of various media samples provided by the sponsors;
(2) Physical relaxation processes involved in damping and corresponding contributions to and
weight in the total damping constant α ;
(3) Temperature dependence of the damping constant α and its components;
(4) Level of inhomogeneity or level of spatial variation in the anisotropy field;
(5) Effects of material parameters and properties on the damping constant α ;
(6) Contributions of magnon-magnon scattering processes to the relaxation (for fields pointed away
from the film normal direction);
(7) Research opportunities for two graduate students, two undergraduate students, and one high
school student;
(8) Three quarter reports and one final report;
(9) Two or more joint publications with industry partners;
(10)Development and enhancement of collaborations with recording industry.
g. Time Line
Table III gives the work schedule for the proposed project. As the project proceeds, we will redefine
this schedule according to our progress to maximize the output of this project.
9
Table III. Schedule for proposed work
Task
Quarter
1
2
3
Temperature-dependent FMR measurements and numerical analyses
X
X
X
X
X
Frequency-dependent FMR measurements and numerical analyses
Effects of media parameters and properties on damping
X
Polar-angle-dependent FMR measurements and numerical analyses
Reporting
4
X
X
X
X
X
X
III. Research Resources
a. Qualification of Research Team
The PI’s group at Colorado State University (CSU) is ideally suited to implement the proposed project.
There are three main reasons as follows.
(1) The PI’s group has extensive experiences in studying damping in magnetic materials, including
media and head materials from the magnetic recording industry [9,13,14], and in studying microwave
assisted magnetization reversal (MAMR) [15,16,17,18,19]. The PI has published over 80 technical
papers in the field of microwave magnetics, which include nine recent papers in Physical Review Letters.
(2) The team has previous and ongoing collaborations with many scientists in the recording industry
in the field of damping and MAMR. These collaborations were supported in part by research grants from
Western Digital, Seagate, and the Information Storage Industry Consortium (INSIC).
(3) The team has sufficient facilities for FMR measurements over a wide range of magnetic fields (up
to 2 T), as a function of field angle (-90° to 90°), over a wide range of frequencies (up to 75 GHz), at low
and high power (up to 2000 W), and as a function of temperature (100 K to 400 K). Key equipment in PI’s
laboratory includes a 110 GHz vector network analyzer, a 67 GHz vector network analyzer, a 26 GHz
spectrum analyzer, a 40 GSa/s 12 GHz oscilloscope, a 2000 W 8-18 GHz TWT amplifier, a 60 GHz
microwave probe station, and various microwave generators, pulse generators, and electromagnets.
b. Resources Required to Perform Project
The research team for this project will consist of the PI, two graduate students, two undergraduate
students, and one high school student.
The team has sufficient experimental resources for the proposed work, which include seven FMR
systems, a SQUID magnetometer, a MOKE system, and a vibrating sample magnetometer.
The temperature-dependent FMR measurements will be done with either the X-band EPR system or
the K-band low-temperature FMR system.
For the measurements with the EPR system, one first
magnetizes the sample to saturation with a strong magnetic field along the media film normal direction
and then run FMR measurements with a field which is opposite to the direction of the magnetization. This
10
arrangement allows for the observation of FMR responses in the X-band frequency range. It is also
relevant to practical data writing processes where one always applies an opposite field in order to switch
the magnetization.
The frequency-dependent FMR measurements will be done with a high-sensitivity microwave probe
station, which was developed very recently in the PI’s laboratory under a financial support from the U.S.
National Institute of Standard and Technology (NIST). The key components of this station includes a 110
GHz vector network analyzer system, 50 Ω 67 GHz coplanar waveguide structures and calibration kits, 50
Ω 67 GHz probes, 67 GHz low-noise cables with a shielding effectiveness of -120 dB, a 2.4 T
electromagnet, and a pneumatically isolated table for vibration reduction. We will also consider the use of
microwave cavities of different frequencies. High-Q cavities available for this project include a 9.45 GHz
cavity, a 9.48 GHz cavity, and a 17.3 GHz cavity.
c. Resources Other Than ASTC Funding Dedicated to Perform Project
Below is a list of the current support of the PI, which will support either directly or indirectly the
implementation of this new project.
Title: New Faculty Startup Funds
Source of Support: Colorado State University
Starting Date: 09/16/2007
Ending Date: 08/15/2012
Amount: $333,000
Principal Investigator: Mingzhong Wu
Title: Nonlinear spin waves in magnetic films: new concepts and applications
Source of Support: The U.S. National Science Foundation
Project Location: Department of Physics, Colorado State University
Award Amount: $330,000
Starting Date: 09/01/2009
Ending Date: 08/31/2012
Principal Investigator: Mingzhong Wu
Co-Principal Investigator: Lincoln Carr
Project Title: Novel magnetic nano films and devices for millimeter wave communications
Source of Support: The U.S. National Science Foundation
Project Location: Department of Physics, Colorado State University
Award Amount: $328,000
Starting Date: 09/01/2007
Ending Date: 08/31/2011
Principle Investigator: Mingzhong Wu
Co- Principle Investigator: Carl E. Patton
11
Project Title: Measurement/characterization of nanometer-scale magnets for post-CMOS electronics
Source of Support: The U.S. National Institute of Standard and Technology
Project Location: Department of Physics, Colorado State University
Award Amount: $962,440
Starting Date: 01/01/2010
Ending Date: 12/31/2012
Principal Investigator: Kristen Buchanan
Co-Principal Investigator: Mingzhong Wu
Co-Principal Investigator: Carl Patton
Project Title: High-frequency measurements and analysis on Western Digital materials and devices
Source of Support: Western Digital Technologies, Inc.
Project Location: Department of Physics, Colorado State University
Award Amount: $10,000
Starting Date: 01/04/2011
Ending Date: 06/30/2011
Principle Investigator: Mingzhong Wu
d. Resources Requested from ASTC
Table IV gives a summary of the budget for this project. The Colorado State University’s federally
negotiated indirect cost rates for research is 48.0%, modified to exclude capital equipment and tuition.
The fringe rates for the faculty, graduate research assistants, and students hourly are 25.3%, 4.9%, and
0.8%, respectively. The budget includes the following items.
(1) Support is requested for 0.25 summer month salary for the PI, 10 months for one graduate
student, and 3 months for another graduate student.
Support is also requested for one
undergraduate “work study” student and one undergraduate “non-work study” student. One high
school student will also participate in this research project, but under support from the summer
Research Engineering Apprenticeship Program (REAP) of the U. S. Army Research Office.
(2) Monthly operating costs are requested for materials, supplies, and facility use fees.
The
materials and supplies include supplies for sample preparations, electronic components for
measurement systems, and computer software for numerical analyses.
(3) Tuition cost is requested for one semester of in-state graduate tuition.
(4) Travel funds are requested to partially support the PI and the students to present the results at
ASTC meetings and other conferences.
12
Expected technical cooperation with the sponsors: We expect that the sponsors will provide recording
media samples and relevant information about the samples, such as saturation magnetizations,
anisotropy fields, film thicknesses, and grain sizes.
Table IV. Budget summary
PERSONNEL SALARIES
Academic Faculty:
Fringe Rate
Administrative Professional:
Fringe Rate
State Classified:
Fringe Rate
Post-Doctorates:
Fringe Rate
Non-Student Hourly:
Fringe Rate
Student Hourly:
Fringe Rate
GRA's:
Fringe Rate
$1,958
$495
$0
$0
$0
$0
$0
$0
$0
$0
$6,000
$40
$22,750
$1,115
TOTAL SALARY:
TOTAL FRINGE:
$30,708
$1,650
TOTAL PERSONNEL:
$32,358
DOMESTIC TRAVEL:
$2,000
INTERNATIONAL TRAVEL:
$0
MATERIALS AND SUPPLIES
$10,236
OTHER DIRECT COSTS
In-State Tuition:
Out-State Tuition:
Publications:
Participant Stipends:
Participant Allowances:
Participant Travel:
Equipment Use Fees:
Animal Care:
Consultants:
Other:
$3,996
$0
$0
$0
$0
$0
$0
$0
$0
$0
TOTAL OTHER DIRECT:
$3,996
SUBCONTRACTS:
$0
EQUIPMENT:
$0
TOTAL DIRECT COSTS:
$48,590
Facilities & Administrative:
$21,405
Consortium F&A
TOTAL:
$0
$69,995
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Expected student internships: We expect that the sponsors will provide a summer internship
opportunity for one of the two graduate students in this project.
IV. Biographical Sketch of Principal Investigator
Dr. Mingzhong Wu is an Assistant Professor in the Department of Physics, Colorado State University
(CSU). His research group is interested in many topics in microwave magnetics. The current research
areas include ferromagnetic resonances and relaxation, magnetization reversal dynamics, spintronics,
microwave and millimeter wave magnetic materials and devices, multiferroic heterostructures, and
nonlinear spin waves. Dr. Wu has been a Senior Member of the Institute of Electrical and Electronic
Engineers (IEEE) since 2006. He has been on the Education Committee of the IEEE Magnetics Society
since 2009 and on the Editorial Review Board of IEEE Magnetics Letters since 2010. He serves as a
proposal reviewer for six research foundations, and he also serves as a reviewer for 28 international
journals.
He has served on organizing and program committees for a number of international
conferences. He received the Early Career Faculty Excellence in Undergraduate Teaching or Mentoring
Award from the CSU College of Natural Sciences in 2011. Dr. Wu has authored and co-authored over 80
publications in archival technical journals.
V. References
1
M. Sparks, Ferromagnetic-Relaxation Theory (McGraw Hill, New York, 1964).
2
A. G. Gurevich and G. A. Melkov, Magnetization Oscillations and Waves (CRC-Press, Boca Raton,
1996).
3
V. Kambersky, Phys. Rev. B 76, 134416 (2007).
4
K. Gilmore, Y. U. Idzerda, and M. D. Stiles, Phys. Rev. Lett. 99, 027204 (2007).
5
S. S. Kalarickal, N. Mo, P. Krivosik, and C. E. Patton, Phys. Rev. B 79, 094427 (2009).
6
B. Heinrich and G. Woltersdorf, J. Supercond. Novel Magn. 20, 83 (2007).
7
J. Zhu, X. Zhu, and Y. Tang, IEEE Trans. Magn. 44, 1 (2008).
8
P. Krivosik, S. S. Kalarickal, N. Mo, S. Wu, and C. E. Patton, Appl. Phys. Lett. 95, 052509 (2009).
9
L. Lu, M. Wu, M. Mallary, G. Bertero, K. Srinivasan, and R. Acharya, “Ferromagnetic resonance and
damping in perpendicular recording media,” in preparation.
10
J. Kunes and V. Kambersky, Phys. Rev. B 65, 212411 (2002).
11
N. Mo, J. Hohlfeld, M. ul Islam, C. S. Brown, E. Girt, P. Krivosik, W. Tong, A. Rebei, and C. E. Patton,
Appl. Phys. Lett. 92, 022506 (2008).
12
S. S. Kalarickal, P. Krivosik, J. Das, K. S. Kim, and C. E. Patton, Phys. Rev. B. 77, 054427 (2008).
13
“Effects of seed layers on ferromagnetic resonance linewidths of Fe65Co35 thin films,” Lei Lu, Ke Sun,
Mingzhong Wu, Jared Young, Christoph Mathieu, and Matthew Hadley, the 2009 APS Four Corners
Section Fall Meeting, Golden, Colorado, October 23-24, 2009.
14
14
“Origins of damping in ultra-thin ferromagnetic films,” Lei Lu, Zihui Wang, Griffin Mead, Mingzhong Wu,
Christian Kaiser, and Qunwen Leng, the 2010 APS Four Corners Section Fall Meeting, Ogden, Utah,
October 15-16, 2010.
15
“Simulation of microwave assisted magnetization reversal in perpendicular-anisotropy thin films,”
rd
Mingzhong Wu, Zihui Wang, and Corneliu Nistor, the 53
Annual Conference on Magnetism and
Magnetic Materials, Austin, Texas, November 10-14, 2008. (Invited talk)
16
“Observation of microwave-assisted magnetization reversal in magnetic films through ferromagnetic
resonance absorption measurements,” Mingzhong Wu, Zihui Wang, Corneliu Nistor, and Ke Sun, the
th
20 Magnetic Recording Conference, Tuscaloosa, Alabama, October 5-7, 2009. (Invited talk)
17
Z. Wang and M. Wu, J. Appl. Phys. 105, 093903 (2009).
18
C. Nistor, K. Sun, Z. Wang, M. Wu, C. Mathieu, and M. Hadley, Appl. Phys. Lett. 95, 012504 (2009).
19
Z., Wang, K. Sun, W. Tong, M. Wu, M. Liu, and N. Sun, Phys. Rev. B 81, 064402 (2010).
15