Fabrication and properties of spin dependent tunneling junctions with CoFeHfO as free layers

Abstract

Spin-dependent tunneling (SDT) structures of Ta–Cu–Ta–CoFeHfO–Al2O3–FeCo–CrPtMn have been deposited by rf diode sputtering. The junctions have been fabricated using photolithographic techniques. A junction magnetoresistive ratio as high as 34% has been obtained after annealing the junctions at 250 °C for 1 h. The junctions have a typical bias voltage of 475 mV at half-maximum magnetoresistance values. The resistance–area–product is about 1 MΩ μm2, and the dc breakdown voltage is about 1.5 V. AlN has also been investigated as a barrier for the junctions. CoFeHfO layers have a high in-plane induced anisotropy field of 65 Oe and a high 4πMs value of 1.2 T, leading to a ferromagnetic resonance frequency higher than 2 GHz. This material has a high bulk resistivity of 1000 μΩ cm, resulting in a small eddy current effect. Therefore, a SDT device with CoFeHfO as the free layer is an attractive candidate for high-speed applications.

Tuning Magnetic Microstructures of Reference Layer in Magnetic Tunneling Junctions

“…A magnetic field of 4 kA/m was applied during the magnetic layer deposition to induce the easy axis. Annealing was done in forming gas at a temperature of 250 C for 1 hour with an applied field of 318 kA/m to align the pinning layer structure [11]. The antiferromagnetic (AFM) CrMnPt layer for pinning is at the top.…”

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

“…Hayakawa et al [10] first reported that Fe-M-O (M = Hf, Zr) magnetic films possessed a good magnetic softness owing to their nanostructure which consisted of ferromagnetic bcc nanocrystals (∼10 nm in size) embedded in an amorphous matrix containing large amounts of M and O elements. Soon after this work, several attempts were made to improve the high-frequency performance of these films [11][12][13][14][15][16][17][18][19]. It was found that the addition of Co to Fe-Hf-O films led to a significant improvement in the high-frequency magnetic response, mainly due to an increase in the crystalline anisotropy of the nanograins.…”

“…In this context, the recent findings of new magnetic oxide thin films are of practical importance in high-frequency applications because these materials can show a good highfrequency performance into the gigahertz range owing to their resistivity, which is approximately ten times higher than that of conventional magnetic alloy films [6,7,[10][11][12][13][14][15][16][17][18][19]. Hayakawa et al [10] first reported that Fe-M-O (M = Hf, Zr) magnetic films possessed a good magnetic softness owing to their nanostructure which consisted of ferromagnetic bcc nanocrystals (∼10 nm in size) embedded in an amorphous matrix containing large amounts of M and O elements.…”

“…Sato et al [11,12] revealed that magnetic inductors using Co-Fe-Hf-O thin films had a higher quality factor and conversion efficiency than those using Fe-Hf-O and Co-Ta-Hf thin films. Since the Co-Fe-Hf-O thin films are insensitive to oxygen at interfaces, they could also be used as free layers for fabrication of spin-dependent tunnelling (SDT) junctions [16] and as electrode layers for tunnelling magnetoresistive (TMR) junction applications [17]. It was shown that the structure of a Co-Fe-Hf-O film consisted of α-Fe(Co)-rich bcc nanograins embedded in a HfO 2 -rich amorphous matrix [10,17,19].…”

“…Recently there has been an emerging demand for the use of magnetic thin films in high-frequency applications including magnetic recording write-heads and soft underlayers for perpendicular media and thin film wireless inductor cores [6,7,[10][11][12][13][14][15][16][17][18][19]. For these applications, magnetic thin films are required to have high electrical resistivity (ρ) to minimize energy loss due to eddy currents, and a large saturation magnetization (4π M s ) and hard-axis anisotropy field (H kH ) to increase the magnetic switching capacity at high frequencies [7,10].…”