Tailoring Curie temperature and magnetic anisotropy in ultrathin Pt/Co/Pt films

Abstract

The dependence of perpendicular magnetization and Curie temperature (Tc) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pts) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the Tc was measured using SQUID magnetometer. We have observed a systematic dependence of Tc on the thickness of Pts. For 8nm thickness of Pts the Co layer of 0.35nm showed ferromagnetism with perpendicular anisotropy at room temperature. As the thickness of the Pts was decreased to 2nm, the Tc went down below 250K. XRD data indicated polycrystalline growth of Pts on SiO2. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5nm)/Pt(3nm)/Co(0.35nm)/Pt(2nm) had much higher Tc (above 300K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic Tc and anisotropy by varying the Pts thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pts layer which hosts the Co layer.

Asymmetric modification of the magnetic proximity effect in Pt/Co/Pt trilayers by the insertion of a Ta buffer layer

“…It has been observed that with larger Ta thickness, the growth of Pt(011) becomes more prominent than Pt(111). Similar growth has been observed in our recent work [46]. X-ray diffraction (XRD) has been carried out on these bilayers (shown in the supplemental material [47]).…”

Structural and morphological effect of Ti underlayer on Pt/Co/Pt magnetic ultra-thin film

“…Due to texture growth in the fcc (111) orientation, it was not surprising to obtain PMA in the tpcp sample rather than the randomly oriented pcp sample. Similar studies have been carried out using different underlayers such as Ta and TaOx (3-5nm) [13,30,35]. The underlayer promotes (111) orientation growth and leads to enhance PMA.…”

“…[8][9][10], L10 ordered tetragonal structures (CoPt,FePt) [11,12], HM/FM/HM (Pt/Co/Pt, Ir/Co/Pt etc.) trilayers [13][14][15] and rare earth-transition metal alloy films(TbFeCo, GdFeCo etc.) [16,17]can be used as a strong PMA structure.…”

“…Generally, strong spin-orbit coupling at FM and HM interface causes PMA, and PMA strongly depends on FM and HM layer thicknesses [13,18,19], growth parameters [20][21][22][23], and structural parameters such as surface roughness [2,24], diffusion [9,25,26], and strain [8,27,28]. Also, it's well known that the textured growth in fcc (111) orientation helps to promote/enhance PMA, and it can be achieved by inserting underlayers/buffer layer such as Pt, Ta, and TaOx as a template for crystalline growth between the substrate and the bottom layer [8,13,21,23,29,30]. Although the enhancement of PMA by using a buffer/under layer was extensively studied, the reason behind this behavior was not completely emphasized.…”

Numerical Analysis of an Active Thermomagnetic Device for Thermal Energy Harvesting

“…Geometric aspects influence energy density and incorporation within the harvesting cycle, thus the gap distance and Gd thickness were also varied. Though Gd has a Curie temperature of 293 K [28], methods to increase Curie temperatures through material layering or alloying are possible [20,29]. Thus, the influence of heat source temperature variance and Curie temperature on device efficiency was also evaluated.…”