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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Ferromagnetic resonance in tunnel junctions: Mag-noise and complex impedance analysis

Valeri Synogatch, Neil Smith, and J. R. Childress

J. Appl. Phys. 93, 8570 (2003); http://dx.doi.org/10.1063/1.1557852 (3 pages) | Cited 3 times

Online Publication Date: 9 May 2003

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Ferromagnetic resonance (FMR) in the Co80Fe20/Ni80Fe20 free (sense) layer of micron-sized, magnetic tunnel junction (MTJ) devices is studied by two different techniques. The first method employs the MTJ device’s magnetoresistance, and measures thermally excited magnetization fluctuations (mag-noise) as a resistance noise spectrum. Correlations between magnetoresistance and FMR frequency versus in-plane magnetic field have been observed for different devices. The FMR frequencies agreed well with calculations when including substantial out-of-plane magnetic anisotropy fields. The second method detects the change in the complex impedance of the MTJ before and after applying a dc current, as measured by a vector network analyzer. The latter method seems to be very sensitive to internal nonuniform states of the free layer magnetization. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Np Metals and alloys
75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy

Noise in magnetic tunnel junction devices

K. B. Klaassen, J. C. L. van Peppen, and X. Xing

J. Appl. Phys. 93, 8573 (2003); http://dx.doi.org/10.1063/1.1557764 (3 pages) | Cited 15 times

Online Publication Date: 9 May 2003

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The noise expected from an ideal magnetic tunnel junction (MTJ) head is thermal noise at low bias voltages (≪50 mV, thermally assisted barrier crossings) and shot noise at higher bias voltages (≫50 mV, field-assisted barrier crossings). The shot noise is larger than the thermal noise, therefore, at 200 mV, the signal of an MTJ head has to be a factor of 2 larger than that of a GMR head with the same resistance to realize the same SNR. This paper reports MTJ noise measurements up to the ferromagnetic resonance (1–2 GHz). An ultra low-noise pre-amplifier system is described that allows electrical biasing of the devices. Wide-band 1/f noise is observed in devices without proper hard bias. Saturation is used to assess the magnetic fluctuation noise and the resonance therein. These wide-band noise measurements demonstrate that one can electronically read out MTJ heads up to the ferromagnetic resonance and down to the noise floor. © 2003 American Institute of Physics.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.

Thermal magnetization noise in submicrometer spin valve sensors

Vassilios D. Tsiantos, Thomas Schrefl, Werner Scholz, and Josef Fidler

J. Appl. Phys. 93, 8576 (2003); http://dx.doi.org/10.1063/1.1557853 (3 pages) | Cited 4 times

Online Publication Date: 9 May 2003

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With decreasing device dimensions thermal fluctuations may ultimately limit the performance of spin valve sensors. Using finite element micromagnetic simulations, we investigate thermal magnetization noise in submicrometer soft magnetic sensor elements within the framework of Langevin simulations. Local random thermal fluctuations lead to a collective motion of the magnetization. The magnetization precesses in the end domains leading to an oscillation of the total magnetization parallel to the long axes with an amplitude in the order of 0.1 Ms at 350 K. The noise power increases linearly with temperature. Irrespective of the bias field, the time averaged total magnetization parallel to the long axes decays approximately by 0.01 Ms as the temperature is raised by 100 K. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.75.Ss Magnetic field sensors using spin polarized transport
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Thermally excited ferromagnetic resonance as diagnostic tool for spin valve heads

Yuchen Zhou, Jian-Gang Zhu, and Nayoung Kim

J. Appl. Phys. 93, 8579 (2003); http://dx.doi.org/10.1063/1.1557854 (3 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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Thermally excited ferromagnetic resonance (TEFMR) in a spin valve head gives rise to mag-noise while its power spectral density directly reflects the magnetic field distribution in the sensing layer as well as the corresponding micromagnetic states. In this article, we report an experimental study on utilization of TEFMR spectral characteristics for spin valve head diagnosis and characterization. The study suggests that the variation of the micromagnetic states in the PM layer at the junctions is one of the most important factors causing the head-to-head variations of the recording performance, especially the heads from the same wafer. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.47.De Giant magnetoresistance
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
75.50.Ss Magnetic recording materials
85.75.Ss Magnetic field sensors using spin polarized transport

Experimental study of signal dependent noise in perpendicular recording

Wenzhong Zhu, Jian Chen, David Kaiser, Jack Judy, and Dean Palmer

J. Appl. Phys. 93, 8582 (2003); http://dx.doi.org/10.1063/1.1557765 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The extracted dipulse technique, or pseudorandom sequence method, has been used to determine the dependence of the noise upon the signal. Four main types of echo are identified. A simple model is developed and the simulated waveforms are used to substantiate the physical interpretation of the noise echo pulse. The model takes into account the most significant eigenmodes of noise obtained from experimental dibit data at different linear densities using a Karhunen–Loeve expansion. The calculations and experimental data agree very well from low linear density up to high linear density where the supralinear noise occurs. © 2003 American Institute of Physics.
Show PACS
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
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