Laser ablated pure non-crystalline Co thin films for inductors for ultra-high frequencies
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Laser ablated pure non-crystalline Co thin films for inductors for ultra-high frequencies
V. Madurga, J. Vergara, C. Favieres Departamento de Física. Universidad Pública de Navarra. Campus Arrosadía. E-31006 Pamplona. Spain. ABSTRACT Non-crystalline Co thin films have been prepared by pulsed laser ablation deposition. From the M-H hysteresis loops measurements, a soft magnetic behavior is observed. Néel type magnetic domain walls are observed in the as-deposited films. The spontaneous magnetization, Ms (T = 300 K), is ≈ 860 emu/cm3. After annealing at 500 oC, Ms (T = 300 K) is ≈ 1460 emu/cm3. The extrapolated to zero K resistance decreases almost two orders of magnitude from the as deposited samples to the crystallized heated at 500 °C ones. A trilayer Co/Cu/Co has shown a real part magnetic susceptibility of 120 at 100 MHz. In the 100 MHz to 1 GHz frequency range, a perpendicular bias magnetic field increased this value up to 270, remaining almost constant for all range.
INTRODUCTION Ferromagnetic elements in the amorphous state have attracted interest from both the theoretical and the applied points of view [1-9]. Different techniques have shown the possibility of producing these kind of materials; in particular, the pulsed laser ablation deposition method, PLAD, is one of the most versatile method for preparing non-crystalline solids [7] and thin films of pure ferromagnetic elements at room temperature [8-9], exhibiting interesting magnetic and electrical properties. Since years, there has been interest in developing thin film soft ferromagnetic materials appropriated for high frequency ( f >100 MHz) applications, as for example, for electromagnetic devices as a high frequency field-amplifying component, e.g., in read-write heads for magnetic disk memories for computers [10-12]. Some of the most desirable properties in these materials are high saturation magnetization, low magnetic coercitivy, high magnetic permeability and high electrical resistivity. In this work we show that non-crystalline PLAD Co thin films - films made up of one element only -, are very suitable for high frequencies applications because they exhibit, at room temperature, such magnetic and electrical properties mentioned above.
EXPERIMENTAL Non-crystalline Co thin films were prepared by PLAD, using a stainless-steel chamber (Neocera) at 10-5 mbar pressure. A pulsed Nd: YAG laser, λ=1024 nm, 20 Hz repetition rate, with 4 ns pulses, energy 300 mJ per pulse, was used. A polished circular disk, 20 mm in diameter, of pure Co (Goodfellow metals, 99.999%) was used as the target, which was rotated at 32 rpm. The area of the laser beam on the target was 2 mm2. Pure Si (111) substrates, 2 X 25 T3.2.1
mm2, were used for depositing the CoCuCo sandwiches and 4 x 4 mm2 substrates were used for the pure Co films deposition. The substrates, which were rotated at 120 rpm, were situated at 70 mm from the target. The deposition time was 30 min., thus obtaining samples ≈ 250 nm thick. After deposition, some samples were annealed at temperatures up to 700 °
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