Magnetoresistance in amorphous oxide films CoFeHfO

Abstract

This paper shows results on structural and magnetotransport measurements for reactively sputtered amorphous oxide films (Co55Fe20Hf25)1 − xOx with x ⩽ 0.35 and their layered structures. A strong x-dependency was found to be related to microstructural changes caused by oxygen-induced chemical phase separation. For low x, Co–Co(Fe) pair-correlated atom clusters dominate and the films are soft ferromagnetic with excellent uniaxial magnetic anisotropy. Small coercivity Hc ≈ 1–4 Oe, enhanced magnetisation Ms ≈ 420 emu/cm3 and low resistivity ρ ≈ 10− 4 Ωcm were measured for these films, showing a good potential for application in magnetoelectronics. For large x, however, since Hf-O pair-correlated atom clusters are dominant, the films become granular-like superparamagnetic with a saturation field Hs>20 kOe and a remanence Mr/Ms ≈ 0. ρ is extremely high presumably due to Coulomb blockade effect. A large magnetoresistance was observed, being 30% (70 kOe) at 5 K and 10% at room temperature. This effect can be attributed to spin-dependent tunnelling among lateral separated Co-Co(Fe) clusters. The layered structure shows a small, but low-field magnetotunnelling effect.

Driving ferromagnetic resonance frequency of FeCoB/PZN-PT multiferroic heterostructures to Ku-band via two-step climbing: composition gradient sputtering and magnetoelectric coupling

“…Microwave soft magnetic films (SMFs) are key materials, which can effectively miniaturize and multifunctionalize the electromagnetic components and devices, such as filters, phase shifters, isolators, circulators, thin film wireless inductors, magnetic recording write heads, antennas, etc 3456,. and reduce their occupation area in MMIC boards.…”

Novel nanostructure and magnetic properties of Co–Fe–Hf–O films

“…In fact, when the sputtering is carried out in an Ar atmosphere (P O2 = 0%), the atmosphere preferentially reacts with Co and Hf forming clusters of Fe-Fe(Co) and Co 2 Hf due to chemical phase separation [19]. This is verified by the TEM image (figure 2(a)) and the selected area diffraction (SAD) pattern (inset of figure 2(a)).…”

Large tunable FMR frequency shift by magnetoelectric coupling in oblique-sputtered Fe 52.5 Co 22.5 B 25.0 /PZN-PT multiferroic heterostructure

“…[1] Microwave soft magnetic films (SMFs) are key materials for reducing the footprint of magnetic components on monolithic microwave integrated circuit (MMIC) boards. [2,3] The functioning frequency, performances, and size of the magnetic microwave components in MMICs, such as magnetic inductors, phase shifters, circulators, isolators, and filters, primarily dominate ferromagnetic resonance (FMR) frequency f r and the permeability µ of the SMFs. [4][5][6][7][8][9] The developing trend of MMICs toward high integration, high frequency, light weight, low energy consumption, etc., requires that SMFs should exhibit higher f r , larger µ, and good compatibility with IC fabrication processes.…”