Magnetic tunnel junctions (MTJs) have been identified as promising candidates for the development of high-performance, ultra-low field magnetometers due to their high sensitivity, low cost, low power consumption, and small size. However, 1/f noise is often quite large at low frequencies and inevitably becomes one of the most difficult issues in developing a magnetic field sensor with ultrahigh sensitivity. Low-frequency 1/f noise can have both electric and magnetic origins, and it is a result of complex non-linear interactions between many degrees of freedom inside a sensor. Therefore, a reduction of the 1/f noise can be expected for the magnetic sensor with very small dimensions. Here, the dependence of the 1/f noise on voltage and strong hard-axis bias field in deep submicrometer-sized MgO-based MTJs is investigated with various junction sizes. The noise spectra were measured by using a home-built low-frequency noise measurement setup with maximum frequency up to 30 kHz. We find that the noise spectral power density is 1/f-like at low frequencies. The experimental results suggest a relative reduction of 1/f noise with respect to the intrinsic thermal noise in small-sized MTJs. The results may open a new approach for reducing the 1/f noise level in MTJ nanosensors.
Complex magnetic ordering in a porous [Co/Pd]5-IrMn multilayered film is modeled for interpreting its magnetization reversal and magnetoresistance mechanisms and explaining its high-resistive and low-resistive states in opposite external fields.
The ribbons Nd2Fe14B/Fe-Co were prepared with the nominal composition Nd16Fe76B8/40% wt. Fe65Co35by the conventional and the developed magnetic field-assisted melt-spinning (MFMS) techniques. Both ribbons are nanocomposites with the smooth single-phase-like magnetization loops. The 0.32 T magnetic field perpendicular to the wheel surface and assisting the melt-spinning process reduces the grain size inside the ribbon, increases the texture of the ribbon, improves the exchange coupling, and, in sequence, increases the energy product(BH)maxof the isotropic powdered samples of MFMS ribbon in ~9% by comparison with that of the ribbon melt-spun conventionally. The grain size reduction effect caused by the assisted magnetic field has also been described quantitatively. The MFMS technique seems to be promising for producing high-performance nanocomposite ribbons.
In this study, we consider a technological approach to obtain a high perpendicular magnetic anisotropy of the Co/Pd multilayers deposited on nanoporous TiO2 templates of different types of surface morphology. It is found that the use of templates with homogeneous and smoothed surface relief, formed on silicon wafers, ensures conservation of perpendicular anisotropy of the deposited films inherent in the continuous multilayers. Also, their magnetic hardening with doubling of the coercive field is observed. However, inhomogeneous magnetic ordering is revealed in the porous films due to the occurrence of magnetically soft regions near the pore edges and/or inside the pores. Modeling of the field dependences of magnetization and electrical resistance indicates that coherent rotation is the dominant mechanism of magnetization reversal in the porous system instead of the domain-wall motion typical of the continuous multilayers, while their magnetoresistance is determined by electron-magnon scattering, similarly to the continuous counterpart. The preservation of spin waves in the porous films indicates a high uniformity of the magnetic ordering in the fabricated porous systems due to a sufficiently regular pores array introduced into the films, despite the existence of soft-magnetic regions. The results are promising for the design and fabrication of future spintronic devices.
Nd
10.5
Fe
83.5−x
Ga
x
B
6 (x=1.5, 3 and 4.5) ribbons were prepared by melt-spinning method with various wheel speeds from 5 to 40 m
s
−1. Strong crystallographic texture with c-axis of Nd
2
Fe
14
B crystallites along normal of the ribbon surface was observed. The texture degree can be enhanced by decreasing the quenching rate during solidification of the melt and by increasing the concentration of Ga. Preferred orientation of the nanocrystallites with their size of 10–30 nm is obtained not only by controlling the quenching rate of the melt during solidification but also by appropriately annealing the over-quenched ribbons. The texture of microstructure clearly affects magnetic anisotropy of the ribbons. With increasing concentration of Ga, the magnetic anisotropy of the ribbons is considerably increased. The coercivity above 6.5 kOe and maximum energy products larger than 15 MGOe can be achieved on the ribbons with Ga-concentration of 1.5%.
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