Suppression of low-temperature ferromagnetic phase in ultrathin FeRh films

Abstract

Highly ordered B2 FeRh films with sharp magnetic transitions from the antiferromagnetic (AF) to ferromagnetic (FM) states were prepared on thermally oxidized Si wafers with thicknesses as low as 10 nm. It is found that the transition temperature increases as the thickness decreases from 80 nm to 15 nm, and then decreases from 15 nm to 10 nm. While the ratio of the residual magnetization to the maximum magnetization keeps nearly unchanged for the film thickness of 15 nm and larger, it increases significantly when the thickness is reduced to 10 nm. This residual magnetization was suppressed by slightly increasing the Rh atomic content in 10 nm thick FeRh films. Low-pressure deposition is found to play an important role in the stabilization of the AF phase. By depositing FeRh films at an extremely low pressure of 0.057 Pa, a residual magnetization as small as 13.5 emu/cc at 100 K was observed for a film with a nominal thickness of 10 nm deposited on Si wafer. This value was further reduced to 6 emu/cc when the film is deposited on MgO substrates due to much improved FeRh crystallinity. These results are in close agreement with theoretical predictions on defect and interface induced FM stabilization.

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

“…FM AF shown in the inset of figure 8(d) decreases monotonously with the film thickness. The thickness dependence of the magnetic phase transition in FeRh was studied by several groups [4,13,14,35]. Due to the complexities in the FeRh thin film preparation the obtained results are not always mutually compatible.…”

“…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.…”

Gd5(Si,Ge)4 thin film displaying large magnetocaloric and strain effects due to magnetostructural transition

“…24,25 Such artificial multiferroic devices, composed of a piezoelectric and a Gd 5 (Si,Ge) 4 magnetostrictive material, have already presented promising properties for energy harvesting purposes at the micrometric scale. Despite their properties, Gd 5 (Si x Ge 1Àx ) 4 materials were left behind in the nanoscalling race, whereas an increasing number of works have been published on Gd multilayers, 27,28 manganites, [29][30][31] FeRh, 32,33 NiMnGa, 34 and MnAs 35,36 materials and also on the MEMS development and numerical simulations. 22,[37][38][39][40] Concerning the Gd 5 (Si x Ge 1Àx ) 4 materials, there is only one not-successful report of a Gd 5 (Si x Ge 1Àx ) 4 thin film.…”