Modulating Curie Temperature and Magnetic Anisotropy in Nanoscale-Layered Cr2Te3 Films: Implications for Room-Temperature Spintronics (original) (raw)

Room Temperature Ferromagnetism of Monolayer Chromium Telluride with Perpendicular Magnetic Anisotropy

Advanced Materials

The realization of long-range magnetic ordering in two-dimensional (2D) systems can potentially revolutionize next-generation information technology. Here, we report the successful fabrication of crystalline Cr3Te4 monolayers with room temperature ferromagnetism. Using molecular beam epitaxy, the growth of 2D Cr3Te4 films with monolayer thickness is demonstrated at low substrate temperatures (~100℃), compatible with Si CMOS technology. X-ray magnetic circular dichroism measurements reveal a Curie temperature (Tc) of ~344 K for the Cr3Te4 monolayer with an out-of-plane magnetic easy axis, which decreases to ~240 K for the thicker film (~ 7 nm) with an in-plane easy axis. The enhancement of ferromagnetic coupling and the magnetic anisotropy transition is ascribed to interfacial effects, in particular the orbital overlap at the monolayer Cr3Te4/graphite interface, supported by density-functional theory calculations. This work sheds light on the low-temperature scalable growth of 2D nonlayered materials with room temperature ferromagnetism for new magnetic and spintronic devices.

Covalent 2D Cr2Te3 ferromagnet

Materials Research Letters, 2021

To broaden the scope of van der Waals 2D magnets, we report the synthesis and magnetism of covalent 2D magnetic Cr 2 Te 3 with a thickness down to one-unit-cell. The 2D Cr 2 Te 3 crystals exhibit robust ferromagnetism with a Curie temperature of 180 K, a large perpendicular anisotropy of 7 × 10 5 J m −3 , and a high coercivity of ∼ 4.6 kG at 20 K. First principles calculations further show a transition from canted to collinear ferromagnetism, a transition from perpendicular to in-plane anisotropy, and emergent half-metallic behavior in atomically-thin Cr 2 Te 3 , suggesting its potential application for injecting carriers with high spin polarization into spintronic devices. IMPACT STATEMENT A T C of 180 K, a perpendicular anisotropy of 7 × 10 5 J m −3 , and a high coercivity of ∼ 4.6 kG were achieved in covalent Cr 2 Te 3 2D ferromagnets.

Robust room-temperature magnetism of (110)CrO2thin films

Physical Review B, 2009

We have used x-ray magnetic circular dichroism ͑XMCD͒ and ab initio electronic-structure calculation techniques to investigate the magnetic properties of high-quality epitaxial ͑110͒ and ͑100͒ CrO 2 thin films. A relatively larger XMCD was observed on the Cr L 2,3 edge of ͑110͒-oriented CrO 2 films compared to ͑100͒oriented CrO 2 films at room temperature. Analysis of our data with conventional sum rules for 3d elements shows a nearly 50% higher spin moment on ͑110͒ films compared to ͑100͒ orientation, consistent with bulk magnetometry measurements. The orbital moment is found to be similar for both orientations. Robust magnetism is attributed to increased collinearity of Cr spins in strain-free ͑110͒ films as compared to strained ͑100͒ films. Zero-temperature density-functional calculations show opposing trends in nearest-neighbor and nextnearest-neighbor exchange interactions between relaxed and strained CrO 2 .

Two-dimensional chromium pnictides CrX (X=P,As,Sb) : Half-metallic ferromagnets with high Curie temperature

Physical Review B

Using first-principles calculations, we demonstrate that hexagonal monolayers of chromium pnictides CrX (X =P, As, Sb) are ferromagnetically ordered systems with the Curie temperature well above 300 K. All three systems are found to be dynamically stable, having no anomalies in the phonon spectrum. Electronic structure calculations show that CrX are half-metals in a wide energy range, which make them perfect spin polarizers and candidates for observing anomalous Hall effect. Our predictions are robust with respect to external dielectric screening induced, for example, by substrates or encapsulation.

Study of the growth and the magnetism of ultrathin films of Cr on Fe

Surface Science, 2000

The surface magnetic properties of ultrathin Cr films grown on an O/Fe/Ag(100) substrate have been studied by means of spin polarized metastable de-excitation spectroscopy. The presence of oxygen on top of the Fe film inhibits the segregation of Ag and strongly reduces Fe/Cr intermixing. The magnetization of the outermost Cr layer is zero immediately after its deposition, whereas, upon annealing up to 500 K, a net magnetization is observed which reverse its direction as a function of the film thickness already from a 3 ML thick film. The magnetization reversal is in agreement with the layered antiferromagnetic structure of Cr clearly observed for thicker films.

Higher-order contribution and temperature dependence of the magnetic anisotropy in ultrathin films (invited)

Journal of Applied Physics, 1997

The pseudomorphic growth of ultrathin films produces artificial structures, and with it anomalously large magnetic anisotropy energies ͑MAEs͒. Second-and fourth-order MAEs K 2 ,K 4 can be measured and analyzed. To understand the continuous ͑steplike͒ rotation of M in a spin reorientation transition ͑SRT͒, K 4 Ͻ0(K 4 Ͼ0) is necessary. By means of ferromagnetic resonance measurements we show that for fct Ni/Cu͑001͒ the SRT is of second order. It is important to measure the ''surface'' and ''volume'' contribution for all MAE contributions K 2 ,K 4 ,... as a function of temperature. These results are compared with Tϭ0 K first principle electronic structure calculations.

Direct observation of Cr spin polarization in epitaxial Cr/Co/Cr(100) trilayers

Physical Review B, 2013

The spin polarization of chromium at the interface next to a ferromagnetic layer is of general interest because of the competing ferromagnetic and antiferromagnetic exchange coupling. While the Fe/Cr interface has been well studied, information on the Co/Cr interface still remains scarce. Here we show for epitaxially grown Cr/Co/Cr(100) trilayers with smooth interfaces x-ray resonant magnetic scattering (XRMS) results in a saturation field of ±270 mT, recorded at the Co and Cr L 3 edges, respectively. The XRMS results at the Co edge show the expected asymmetry and a ferromagnetic hysteresis for different incident angles θ. Furthermore, XRMS measurements with the energy tuned to the Cr L 3 edge also exhibit an asymmetry, albeit much smaller than the one at the Co L 3 edge. Moreover, the magnetic hysteresis of Cr taken at the L 3 edge has a sign opposite to that of Co at the L 3 edge over a broad range of incident angles. From these results we infer first that at the Co/Cr interface chromium is ferromagnetically polarized, and second that its spin structure is oriented opposite to the magnetization of Co.

Evolution of the magnetic and electronic properties of ultrathin Cr(001) films

Solid State Communications, 2000

We present a spin resolved inverse photoemission study of Cr ultrathin ®lms (up to few monolayers [ML]) grown on Ag and Fe(001) at room temperature. The magnetic properties of the ®lms are strongly in¯uenced by the different interaction with the substrates. For the Cr/Ag(001) system, where the chemical interaction of the overlayer with the substrate is very small, no polarization dependence of the Cr features is observed, a ®nding which can ®t within the predicted antiferromagnetism of a Cr layer. For the case of Cr/Fe(001), the Cr contribution is strongly polarized in the early stages of the interface formation (up to 2 ML) and then becomes gradually unpolarized. q

FIRST-PRINCIPLES STUDY OF MAGNETIC ANISOTROPY ENERGY IN TWO-DIMENSIONAL FERROMAGNETIC CrI3

Indonesian Physical Review

First-principles calculations are increasingly crucial in searching for new materials with customized properties or new functionality. First-principles calculations are superior in speed and cost, and comparable to experiments in terms of accuracy. Two-dimensional (2D) ferromagnetism materials were successfully fabricated experimentally in atomic thin films of CrI3. 2D intrinsic ferromagnetism with perpendicular magnetic anisotropy energy (PMAE) is an encouraging applicant compatible with high-density magnetic storage applications. In this study, spin density functional calculations are investigated on the magnetic anisotropy energy (MAE) in 2D monolayer ferromagnetic CrI3 using a first-principles electronic structure calculation. We include the MAE part calculation from the magnetocrystalline anisotropy energy (MCAE) that comes from the spin-orbit coupling (SOC). In the present calculation, the MCAE part, in addition to a usual scheme of total energy (TE), was evaluated using a gra...