Switching of perpendicular exchange bias in Pt/Co/Pt/α-Cr2O3/Pt layered structure using magneto-electric effect

Abstract

Switching of the perpendicular exchange bias polarity using a magneto-electric (ME) effect of α-Cr2O3 was investigated. From the change in the exchange bias field with the electric field during the ME field cooling, i.e., the simultaneous application of both magnetic and electric fields during the cooling, we determined the threshold electric field to switch the perpendicular exchange bias polarity. It was found that the threshold electric field was inversely proportional to the magnetic field indicating that the EH product was constant. The high EH product was required to switch the exchange bias for the film possessing the high exchange anisotropy energy density, which suggests that the energy gain by the ME effect has to overcome the interfacial exchange coupling energy to reverse the interfacial antiferromagnetic spin.

Magnetoelectric properties of 500-nmCr2O3films

“…This ability to switch the sign of α is a consequence of the reduced Cr 2 O 3 thickness, where the total Zeeman energy associated with the surface magnetization in Cr 2 O 3 becomes comparable to the total ME energy associated with the crystal volume. This conclusion explains previous results [8,[11][12][13] of the electric switching of the exchange bias field in all thin film systems (0001) Cr 2 O 3 /[Co/Pt] n , where it was found that much higher field products E fc H fc are required to achieve the switching compared to bulk single crystals of Cr 2 O 3 .…”

“…The largest field product of |H fc | = 50 kOe and |E fc | = 60 kV cm −1 was not successful, while the films were destroyed for E fc 80 kV cm −1 due to a dielectric breakdown. The lower breakdown field value when compared to previous reports [8,[11][12][13] is likely due to the larger electrode size in our case.…”

“…Since no reflections from Pt bottom electrodes were observed in φ-2θ χ (in-plane) scans, due to the small probing depth and relatively thick Cr 2 O 3 layer, we repeated the same scans for (0001) Al 2 O 3 /Pt 25 (nm) samples and found Pt {2-20} peaks (not shown) for both cases of q probing crystal planes parallel to Al 2 O 3 (10-10) or Al 2 O 3 (11)(12)(13)(14)(15)(16)(17)(18)(19)(20).…”

“…Interestingly, it has already been found that the exchange bias systems made from (0001) Cr 2 O 3 films (150-250 nm) require higher field products E fc H fc to achieve AF single domain switching via ME FC [8,[11][12][13]. In those systems, the AF single domain type is responsible for the switching of the FM hysteresis bias, characterized via the so-called exchange bias field H EB .…”

“…Chromium oxide (Cr 2 O 3 ) has been intensively studied during the last 10 years because it is possible to modulate the exchange bias effect in heterostructures using electric fields [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In the antiferromagnetic (AF) state of Cr 2 O 3 , an applied electric field induces the magnetization, while an external magnetic field induces the dielectric polarization.…”