Microwave Properties and Anisotropy Field Distribution in Nanogranular Fe–Co–Al–O Films

Pasquale, M.,Coisson, M.,Perero, S.,Lim, S.H. IEEE 2005 IEEE transactions on magnetics Vol.41 No.10

We have investigated the microwave properties of a set of Co–Fe–Al–O films with different thicknesses. The films show a well-defined in-plane anisotropy due to the bias field applied during deposition. The resonance frequency is determined through the scattering parameters measured with a vector network analyzer and a probing station connected to a coplanar waveguide. The results show that the resonance peak features depend on the direction of the applied/RF field and on the applied field history.

On the influence of Joule heating induced nanocrystallization on structural and magnetic properties of Co_64Fe_21B_15 alloy

S. N. Kane,M. Coisson,P. Tiberto,F. Vinai,F. Mazaleyrat 한국물리학회 2011 Current Applied Physics Vol.11 No.4

Structural and magnetic properties of Joule heated Co_64Fe_21B_15 alloy have been studied. Crystallization of the specimens starts after Joule heating with 1.6 A current, leading to the formation of nanocrystalline Co_80Fe_20 phase with grain diameter ranging between 19 and 25 nm. Crystallization of the specimens is found to detoriate the soft magnetic properties. Observed decrease of the hyperfine field of the amorphous component upon Joule heating suggests the increase of the boron near-neighbours to iron and the changes in the hyperfine field of the crystalline component are attributed to the changes in the environment around Fe atom in the specimen. The coercivity is found to obey a domain wall pinning process instead of random anisotropy, as expected in soft magnetic nanocrystalline magnetic materials.

Microwave Properties and Damping in [Pt/Co] Multilayers With Perpendicular Anisotropy

Caprile, Ambra,Pasquale, Massimo,Kuepferling, Michaela,Coisson, Marco,Tae Young Lee,Sang Ho Lim IEEE 2014 IEEE magnetics letters Vol.5 No.-

<P>Magnetic tunnel junctions with perpendicularly magnetized elements are being considered for next-generation, non-volatile, magnetic random access memory (MRAM) elements due to their large thermal stability, low Gilbert damping constant α, and very low critical current density Jc required for spin-transfer-torque (STT), current-induced, magnetization switching. Here we study, by means of static magnetization and field-swept ferromagnetic resonance (FMR), [Pt/Co] multilayers with reduced Pt and Co layer thicknesses, ranging between 0.2 nm and 0.32 nm. Such materials are known to exhibit strong perpendicular magnetic anisotropy due to low interdiffusion, even after annealing up to 500°C. We analyzed our data on FMR frequency versus applied magnetic field with the appropriate Kittel formulas and obtained a high anisotropy field H<SUB>k</SUB> and a very low Gilbert damping constant α. This improvement makes the [Pt/Co] system with low overall Pt and Co content a promising candidate for STT-MRAM.</P>

Influence of Composition and Thermal Treatments on Structural, Magnetic and Magnetotransport Properties of (Fe100−xCox)78Si9Nb3B9Cu1 Alloys

S. N. Kane,Zs. Gercsi,F. Mazaleyrat,L. K. Varga,M. Coisson,,F. Vinai,F. Celegato,Y. H. Jeong 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

The effect of Co addition and thermal treatments on the magnetic properties and the corresponding changes occurring in the nanostructure and magnetoimpedance in (Fe100−xCox)78Si9Nb3B9Cu1 with x = 0, 20, 40, 60, 70, 75, 80, 85, 90, 95 are reported. Results show that variation in the Co content affects the stability of the alloy against crystallization and that the specimen with x = 40 exhibits highest stability against crystallization. The volume fraction of the nanograins varies between 42 to 62 % and the corresponding grain diameter ranges between 9 to 13 nm. Obtained lattice parameter values suggest that the studied samples consist of bcc Co-Fe phase with Si impurities, with Co contents ranging between 50 to 74 % and Si contents ranging between 7 to 25 %. In the studied alloys, especially above x = 70, there is a tendency to form and to stabilize a Co70Fe30- like phase. The coercive force for as-cast specimens practically does not change with increasing Co content whereas the samples annealed with and without a magnetic field exhibit appreciable changes and display similar behaviours. The coercive field is systematically lower for field-annealed samples and the abrupt increase in the coercive field for alloys with x = 70 and above is attributed to the formation of a magnetically harder Co70Fe30-like phase (as compared to the Fe80Si20 phase), which were confirmed by a decrease in the lattice parameter. The maximum values of the obtained induced anisotropy constant and the anisotropy field are, respectively, 750 J/㎥ and ~ 1250 A/m. The magnetoimpedance maximum response of the studied samples remains almost constant as a function of Co concentration for the three kinds of samples (as-cast and annealed with and without a field). However, a threefold increase in the linear range is observed for the transverse-field-annealed samples, which should increase the dynamic range of field sensors based on these new materials. The effect of Co addition and thermal treatments on the magnetic properties and the corresponding changes occurring in the nanostructure and magnetoimpedance in (Fe100−xCox)78Si9Nb3B9Cu1 with x = 0, 20, 40, 60, 70, 75, 80, 85, 90, 95 are reported. Results show that variation in the Co content affects the stability of the alloy against crystallization and that the specimen with x = 40 exhibits highest stability against crystallization. The volume fraction of the nanograins varies between 42 to 62 % and the corresponding grain diameter ranges between 9 to 13 nm. Obtained lattice parameter values suggest that the studied samples consist of bcc Co-Fe phase with Si impurities, with Co contents ranging between 50 to 74 % and Si contents ranging between 7 to 25 %. In the studied alloys, especially above x = 70, there is a tendency to form and to stabilize a Co70Fe30- like phase. The coercive force for as-cast specimens practically does not change with increasing Co content whereas the samples annealed with and without a magnetic field exhibit appreciable changes and display similar behaviours. The coercive field is systematically lower for field-annealed samples and the abrupt increase in the coercive field for alloys with x = 70 and above is attributed to the formation of a magnetically harder Co70Fe30-like phase (as compared to the Fe80Si20 phase), which were confirmed by a decrease in the lattice parameter. The maximum values of the obtained induced anisotropy constant and the anisotropy field are, respectively, 750 J/㎥ and ~ 1250 A/m. The magnetoimpedance maximum response of the studied samples remains almost constant as a function of Co concentration for the three kinds of samples (as-cast and annealed with and without a field). However, a threefold increase in the linear range is observed for the transverse-field-annealed samples, which should increase the dynamic range of field sensors based on these new materials.

A Vapor Sensor Based on a Porous Silicon Microcavity for the Determination of Solvent Solutions

Huy Bui,Thuy Van Nguyen,The Anh Nguyen,Thanh Binh Pham,Quoc Trung Dang,Thuy Chi Do,Quang Minh Ngo,Roberto Coisson,Van Hoi Pham 한국광학회 2014 Current Optics and Photonics Vol.18 No.4

A porous silicon microcavity (PSMC) sensor has been made for vapors of solvent solutions, and a method has been developed in order to obtain simultaneous determination of two volatile substances with different concentrations. In our work, the temperature of the solution and the velocity of the air stream flowing through the solution have been used to control the response of the sensor for ethanol and acetone solutions. We study the dependence of the cavity-resonant wavelength shift on solvent concentration, velocity of the airflow and solution temperature. The wavelength shift depends linearly on concentration and increases with solution temperature and velocity of the airflow. The dependence of the wavelength shift on the solution temperature in the measurement contains properties of the temperature dependence of the solvent vapor pressure, which characterizes each solvent. As a result, the dependence of the wavelength shift on the solution temperature discriminates between solutions of ethanol and acetone with different concentrations. This suggests a possibility for the simultaneous determination of the volatile substances and their concentrations.