Structural and magnetic properties of oxide films CoFeHfO: A possible candidate for all-oxide TMR junctions?

Abstract

In search of a magnetic oxide, which is insensitive to oxygen at interfaces and thus appropriate as an electrode layer for tunneling junction applications, we prepared thin films of CoFeHfO by reactive DC-magnetron sputtering technique and investigated the relation between structural and magnetic properties. The results suggest that the films consist of two disorded phases, a Co(Fe)-rich and a HfO-rich. It was found that the degree of film homogeneity and thus the magnetic nature depends on preparation conditions such as film thickness and deposition rate. A second magnetic phase with a high saturation field, which is present in thicker films, could therefore be reduced by decreasing the film thickness. Consequently, the thinnest film (10 nm) is nearly single phased and exhibits an excellent uniaxial anisotropy with a coercive field Hc of 16 Oe along the easy axis. Additionally, thermomagnetic measurements were carried out to understand annealing-induced effects. A clear improvement with increased saturation magnetisation (Ms = 695 emu/cm 3 ) and decreased Hc was observed, which can be attributed to structural relaxation and phase separation caused by annealing.

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

“…For comparison, table 1 summarizes the important parameters of several films that are good candidate materials for magnetic recording and sensor applications. Obviously, the present films exhibit superior properties to the comparison films (table 1) and other films reported in the literature [10][11][12][13][14][15][16][17][18][19]. Among them, the P O2 = 11.5% sample (Co 19.35 Fe 53.28 Hf 7.92 O 19.35 ) exhibits the softest magnetic properties (4π M s = 19.86 kG and H cE = 1.5 Oe) together with a high electrical resistivity (ρ = 3569 μ cm).…”

“…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].…”

Co-rich magnetic amorphous films and their application in magnetoelectronics

“…Its amorphous structure was confirmed before by x-ray scattering experiments, though with a phase separation occurring during the film deposition. 23 The first diffuse peak ͑not shown here͒ is thus slightly split, suggesting two interconnected amorphous phases with nearest atomic correlations dominated by Hf-O and Co-Co͑Fe͒, respectively. Nevertheless, the films show excellent soft magnetic properties with strong uniaxial magnetic anisotropy ͓see Fig.…”

Soft magnetic properties and high frequency characteristics of FeM (M = B, Hf, Zr) and pure Fe films fabricated by oblique deposition

“…During the last decade, much research has been carried out to develop magnetic thin film with excellent high frequency characteristics for application to high-frequency devices such as perpendicular media, magnetic recording write heads and thin-film wireless inductor cores [1][2][3][4][5][6][7]. The highfrequency applications of magnetic thin films require the thin films to possess a high saturation magnetization and an appropriately large in-plane uniaxial anisotropy (IPUMA) [8][9][10][11] field to achieve a high cutoff frequency, which is the highest theoretically possible frequency of soft materials.…”