Magnetic and electrical properties of amorphous CoFeB films

Abstract

CoFeB films were deposited on glass substrate by the sputtering method. From x-ray-diffraction and electron-diffraction-ring patterns, the major phase in the as-deposited CoFeB film is amorphous (or nanocrystalline). However, we could also identify a minor CoFe(110) crystalline phase in the film. We have tried to suppress this crystalline phase by changing the Ar partial pressure (PAr) during deposition and found that the optimal condition is PAr=5×10−3Torr. Because the electrical resistivity value (ρ) of the film is in general larger than 100μΩcm, it also indicates that the amorphous phase is dominant. From the temperature coefficient of resistance measurement, we learn that the amorphous phase in the CoFeB film crystallizes in succession at two higher temperatures (Tcr1 and Tcr2) than the room temperature (RT). Besides the electrical properties, the film thickness (tf) dependence of saturation magnetization (Ms), saturation magnetostriction (λs), and coercivity (Hc) has also been discussed. From the Auger-depth profile analysis, it is found that there is one CoOx (with 0.4⩽x<1) oxide layer, about 15 Å in thickness, lying on the top surface of the CoFeB film, and another CoOx oxide layer, about 20 Å, lying near the CoFeB/glass interface. At RT CoOx is supposed to be paramagnetic. However, due to the proximity effect between CoOx and CoFeB, the CoOx layers may become ferromagnetic with the average magnetization Mox. By fitting the Ms data as a function of (1∕tf), we can show that the last conjecture is correct, and Mox is not zero. The CoOx layer plays an important role on Ms,λs, and Hc of the CoFeB films with tf ranging from 50 to 503 Å.

Scaling of anomalous Hall effect in amorphous CoFeB films with accompanying quantum correction

“…Our study demonstrates the electron localization correction to both sheet resistance R xx and G AH , and displays the scaling relationship of ultrathin amorphous CoFeB films in both Bloch and localization regions. the R xx -t curves of the films at 5 K. One can see that R xx decreases with the increase of t, which can be attributed to the enhanced surface scattering due to the decreased t. The ρ xx of t=2 nm is 1735.8 μΩ cm at room temperature, which is consistent with the reported values of amorphous CoFeB film [21,23]. Fig.…”

“…With the applied field increasing, the magnetization is forced to rotate to the field direction gradually, which results in a linearly field-dependent magnetization until saturation. The magnetization of t=2 nm is nearly 1000 emu/cm 3 , which is much larger than that of magnetite (400 emu/cm 3 ), indicating the nature properties of amorphous CoFeB film [21,33]. The saturation magnetic field of t=40 nm is larger than that of t=2 nm.…”

“…Amorphous CoFeB films have been a subject of extensive studies due to its low coercivity, large saturation magnetization [21,22] and high spin polarization [23], which were widely used in theory research [24,25], magnetic tunnel junctions [26] and spin transfer torque devices [27]. The proper scaling of amorphous CoFeB in the dirty regime without consideration of the quantum correction can be explained by the combination of extrinsic and intrinsic mechanisms quantitatively [28].…”

Anisotropic magnetoresistance of individual CoFeB and Ni nanotubes with values of up to 1.4% at room temperature

“…40 The measured CoFeB resistivity of 1 − 2 × 10 3 μ cm is one order of magnitude larger compared to the best values given in literature for CoFeB alloy films with a comparable thickness. 41,42 For R(T), we do not find a T 3/2 dependence in the accessible temperature range and rule out magnetic contributions to R(T). 43 The characteristic minima in R(T) [Fig.…”

Direct imaging of current-induced domain wall motion in CoFeB structures

“…One of the drawbacks of using CoFeB compared to 3d metals or their alloys is the higher resistivity. 19 In our wire samples the resistivity is about a factor 2.5 higher ͑170 ⍀ cm͒ than for Permalloy wires ͑70 ⍀ cm͒. This means that for identical geometries a voltage that is 2.5 times higher than that used for Permalloy is needed to obtain the same current density.…”