Epitaxial-Strain Effects on Electronic Structure and Magnetic Properties of Hexagonal YMnO3 Thin Films Studied by Femtosecond Spectroscopy

Abstract

In this paper, (001)-oriented hexagonal YMnO 3 (h-YMO) thin films with various nominal strain states were deposited on MgO(100), MgO(111), and YSZ(111) substrates by pulsed laser deposition. The in-plane orientation alignment and substrate-induced epitaxial strain between the h-YMO films and substrates are examined by X-ray diffraction (XRD) θ -2θ , Φ, and ω scans. The effects of epitaxial strain on the on-site Mn d-d transition energy E dd (T ), and the Néel temperature (T N ) in these thin films are investigated by wavelength-tunable ultrafast pump-probe techniques. We find that the changes of E dd (T ) and T N depend on the type and magnitude of the epitaxial strain. The possible mechanisms for the observed strain effect on the electronic structure and associated magnetism are discussed.

Effects of Surface Polarity on the Structure and Magnetic Properties of Epitaxial h-YMnO3 Thin Films Grown on MgO Substrates

“…It is interesting to observe that the in-plane orientation of the h -YMO/MgO (100) exhibits a 12-fold symmetry, whereas the h -YMO/MgO (111) film shows a 6-fold symmetry. In Figures d and e, we simulate the in-plane and out-of-plane atomic arrangements of h -YMO on MgO (100) and MgO (111) substrates, respectively, to replicate the observed in-plane symmetry . According to the principal crystallographic orientations, the h- YMO on MgO (100) substrate can be aligned along either MgO [011] or MgO [01] directions; thus, the angle differences between MgO [010] and the two orientations of h- YMO [110] are 15° and 45°, respectively.…”

“…Multiferroicity is a unique behavior where material could simultaneously possess magnetic and electrical orders that are intimately coupled to each other. − Various multiferroic materials, such as perovskite manganites R MnO 3 ( R : rare earth), have been found to exhibit peculiar magnetoelectric coupling mechanisms. − In particular, thin film YMnO 3 (YMO) becomes one of the highly studied R MnO 3 multiferroics due to its structural and physical tunability by engineering the lattice difference between the film and the substrates; the crystal structure of YMO can be tuned to have orthorhombic ( o- YMO) or hexagonal ( h- YMO) crystalline structure. ,− The resultant phase YMO thin film formed is mainly determined by the lattice matching with the substrates. ,− Nevertheless, several factors, such as surface energy, structure continuity, and chemical bonding at the film–substrate interface, also play important role in giving rise to the final results. − The surface energy and structure continuity render a favorable crystalline direction for film growth, while the chemical bonding drives the in-plane rotation to impose the phase formation of YMO. Hence, the employment of different substrate materials can produce YMO films with various crystal structures, which, in turn, affect the physical properties of the resultant YMO films, such as defect concentration, magnetic behaviors, and so on. ,,− As multiferroic materials, YMO thin films are applicable for various applications, especially next-generation electronic devices. For instance, insertion of the multiferroic layer into magnetic tunnel junction heterostructures enables the realization of a new generation of random access memory (RAM)the so-called magnetoelectric RAM or MERAM .…”

Energy-Resolved Ultrafast Spectroscopic Investigation on the Spin-Coupled Electronic States in Multiferroic Hexagonal HoMnO3

“…On the same time scale, Satoh et al [ 38 ] assigned a relaxation time of approximately 0.9 ps to the demagnetization of AFM compounds. Additionally, previous studies have attributed the few-ps component to electron-lattice relaxation [ 39 , 40 ] or spin-lattice relaxation [ 28 ]. In this paper, we propose a model based on our results as well as those from previous studies.…”

“…The samples used in this study were hexagonal c -axis HoMnO 3 thin films with a thickness of 180 nm. The films were deposited on double-sided polished yttria-stabilized zirconia (111) substrates through pulsed-laser (KrF excimer laser) deposition [ 28 ]. The thin films were employed to measure both the stationary and transient spectra in a transmissivity configuration to obtain high-quality data.…”

“…Time-resolved optical pump-probe spectroscopy is effective for demonstrating and quantifying the interaction strength among quasiparticles and various degrees of freedom [ 22 , 23 , 24 , 25 , 26 ]. This technique has been extensively employed to identify the underlying physical mechanisms of hexagonal manganites [ 27 , 28 , 29 , 30 , 31 ]. However, most previous studies on transient spectroscopy have focused only on the dynamics of the e 2g state, and the other unobservable Mn 3+ d orbits remain unclear.…”