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RESEARCH PAPERS: Micro/Nanoscale Heat Transfer

# Thermal Characterization of $Cu∕CoFe$ Multilayer for Giant Magnetoresistive Head Applications

[+] Author and Article Information
Y. Yang

Mechanical Engineering Department  Carnegie Mellon University, Pittsburgh, PA 15213

R. M. White

Electrical and Computer Engineering Department  Carnegie Mellon University, Pittsburgh, PA 15213

M. Asheghi1

Mechanical Engineering Department and Electrical and Computer Engineering Department,  Carnegie Mellon University, Pittsburgh, PA 15213

1

Corresponding author.

J. Heat Transfer 128(2), 113-120 (Jun 21, 2005) (8 pages) doi:10.1115/1.2136916 History: Received June 10, 2004; Revised June 21, 2005

## Abstract

Giant magnetoresistance (GMR) head technology is one of the latest advancements in the hard disk drive (HDD) storage industry. The GMR head multilayer structure consists of alternating layers of extremely thin metallic ferromagnetic and nonmagnetic films. A large decrease in the electrical resistivity from antiparallel to parallel alignment of the film magnetizations is observed, known as the GMR effect. The present work characterizes the in-plane electrical and thermal conductivities of $Cu∕CoFe$ GMR multilayer structures in the temperature range of $50K$ to $340K$ using Joule-heating and electrical resistance thermometry on suspended bridges. The thermal conductivity of the GMR layer monotonically increases from $25Wm−1K−1$ (at $55K$) to nearly $50Wm−1K−1$ (at room temperature). We also report a GMR ratio of 17% and a large magnetothermal resistance effect (GMTR) of 25% in the $Cu∕CoFe$ multilayer structure.

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## Figures

Figure 1

Tunneling electron micrograph (TEM) of the GMR structure. The GMR layer consists of (from top to bottom) Ta: 30Å; CoFe: 12Å (Co 90%; Fe 10%); 40 repeats: Cu: 21ÅCoFe12Å (Co 90%; Fe 10%); NiFe: 40Å (Ni 80%; Fe 20%) and Ta: 30Å.

Figure 2

Schematic representation of electron transport in a GMR multilayer structure, consisting of top and bottom CoFe magnetic layers and Cu nonmagnetic space layer. The distance between the layers is relatively small compared to the mean free paths of electrons. Large decreases in the electrical and thermal resistivities are expected due to the spin-dependent scattering at the interfaces of the CoFe and Cu multilayer structure.

Figure 3

The fabricated suspended microbridge structure: (a) schematic, and (b) top view image taken using an optical microscope. The dimension ΔL is the length of the over-etched area near the bases of the suspended structure. Voltage pads are connected to the suspended structure by nearly 2‐μm‐wide interconnects.

Figure 4

Changes in the electrical resistances of the suspended bridge as a function of square of current, I2. Curve fits for bridges of the same width and different lengths yield kGMR=51Wm−1K−1, for the GMR layer.

Figure 5

Experimental apparatus for field-dependent measurement

Figure 6

Schematic of the calibration procedure. The R versus I curves for the GMR bridge were measured at different field strength while keeping the base temperature constant. The same process was repeated at different base temperatures.

Figure 7

Temperature dependence of thermal conductivity for Cu∕CoFe GMR multilayer structure. The electrical resistivity is shown in the right inset.

Figure 8

Lorenz number values for 144nm GMR layer of the present study as a function of temperature. The Lorenz number value for free electron is nearly L0=2.45×10−8WΩK−2.

Figure 9

Resistivity change of the 144nmCu∕CoFe GMR multilayer structure as a function of applied field

Figure 10

Thermal conductivity change of the 144nmCu∕CoFe GMR multilayer structure as a function of applied field

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