Phase ordering and its effect on magnetic and structural properties of FeRh ultrathin films

Abstract

Applications using FeRh for controllable exchange coupling of two magnetic layers with in-plane and out-of-plane anisotropies require ultrathin (∼10 nm) films with pure antiferromagnetic (AF) FeRh α″ phase at room temperature (RT). However, it is also well known that the antiferromagnetic-ferromagnetic (AF-FM) transition of FeRh is sensitive to composition and deteriorates at low thicknesses. Hence, in this work, we study the composition-dependent phase ordering of co-sputtered FeRh thin films at ultrathin thicknesses of ∼10 nm. As the ultrathin films get richer in Rh, the appearance of α″ phase is typically characterized magnetically by a sudden drop in RT moment, and structurally by a slight decrease in degree of B2 chemical ordering with a sharp decrease in c-axis lattice constant. These observations are consistent with the FeRh phase diagram where FeRh abruptly enters the AF α″ phase once it becomes slightly disordered. Dependences of magnetic transition parameters on composition were also described. Moreover, higher sputtering powers possibly allow the formation of purer α″ phase with less γ-face centered cubic phase impurities. Consequently, a composition optimized 10 nm film shows a relatively low residual moment (13.5 emu/cc), thus suggesting good AF phase formation. In addition, correlation of the magnetic transition parameters with the crystal structural parameters reveal that the maximum rate of AF-FM transition (Rmax,h) and the corresponding total change in magnetization (ΔMh) interestingly shows linear dependence on the c-axis lattice constant, but would depart from this linearity under certain conditions, i.e., when grain sizes were large, crystallinity was improved and Fe content was high.

Sputter-engineering a first-order magnetic phase transition in sub-15-nm-thick single-crystal FeRh films

“…In this Rapid Communication, we show that, in sharp contrast to previous attempts in which nanothin FeRh alloy films were shown to grow in the Volmer-Weber growth mode [15][16][17][18][19], smooth chemically well-ordered single-crystal fully functional nanothin FeRh alloy films can be synthesized if proper dc-magnetron sputtering deposition parameters are chosen. In particular, we demonstrate that sputter-grown sub-15 nm thick FeRh alloy films deposited at an Ar pressure of about 0.1 Pa onto (001)-oriented MgO substrates grow in an induced Frank-van der Merwe growth mode for t FeRh >5 nm, as consequence of the atompeening [20] effect, i.e.…”

Inhomogeneous spatial distribution of the magnetic transition in an iron-rhodium thin film

“…2c) shows a strong decrease of the total phase shift. From its mean slope extracted on the whole FeRh layer, we obtained a residual magnetization parallel to the film equal to 0.28±0.13 T. This value appears to be higher than previously reported1440.…”

Investigation of magneto-structural phase transition in FeRh by reflectivity and transmittance measurements in visible and near-infrared spectral region

“…Research on FeRh was originally conducted on bulk samples [1,[10][11][12] but more recently, due to the envisioned applications [3,5,8], it focuses on thin films. The desired AF phase is present only for a rather narrow interval of the Fe-to-Rh composition ratios [12], which are achieved experimentally by a variation of the deposition conditions [13][14][15] and by a post-preparation heat treatment [16]. Consequently, the growth of high quality FeRh thin films is a rather complex task which requires a lot of optimisation of the preparation procedure and a deposition of large series of samples [13][14][15][16].…”

“…The desired AF phase is present only for a rather narrow interval of the Fe-to-Rh composition ratios [12], which are achieved experimentally by a variation of the deposition conditions [13][14][15] and by a post-preparation heat treatment [16]. Consequently, the growth of high quality FeRh thin films is a rather complex task which requires a lot of optimisation of the preparation procedure and a deposition of large series of samples [13][14][15][16]. The magnetic phase transition in the prepared films is usually studied by magnetometry, for example by superconducting quantum interference device (SQUID), where not only the phase transition temperature but also the remaining uncompensated magnetic moment in the low-temperature AF phase is measured [14,15].…”

“…Consequently, the growth of high quality FeRh thin films is a rather complex task which requires a lot of optimisation of the preparation procedure and a deposition of large series of samples [13][14][15][16]. The magnetic phase transition in the prepared films is usually studied by magnetometry, for example by superconducting quantum interference device (SQUID), where not only the phase transition temperature but also the remaining uncompensated magnetic moment in the low-temperature AF phase is measured [14,15]. However, the disadvantage of magnetometry is that the magnetic properties are averaged over the whole sample and that it is necessary to subtract the substrate contribution from the measured data.…”