Keywords: Single-phase Multiferroics Lock-in Amplifier Magneto-electric Effect
Note: This article uses the Sine Scientific Instruments OE1022 lock-in amplifier to make measurements.
[Overview]
In 2023, a team of researcher Ma Xiuliang and researcher Zhu Yinlian at the Institute of Metals, Chinese Academy of Sciences, published an article in ACS Applied Materials & Interfaces titled "Achieving High-Temperature Multiferroism by Atomic Architecture", reporting a single-phase multiferroic material coupling high-temperature magnetism with voltage-switchable ferroelectricity. Single-crystal films with uniformly permeable open-shell dn orbitals, consisting of iron cations with B-sites, were prepared using pulsed laser deposition, and they exhibit long-range spin ordering in the displacing ferroelectric PbTiO3 lattice according to atomically resolved chemical analysis.
The tetragonally polar Pb(Ti1-x, Fex)O3(PFT(x), x≤0.10) family has switchable ferroelectric properties with magnetic interactions at room temperature in a moderate coercivity field of alomst 300 Oe and magnetic ordering that persists above 500K, higher than that of the potential multiferroic candidates reported to date. Our strategy of combining spin-ordered sublattices with intrinsic ferroelectricity through atom occupancy engineering provides a viable route to highly thermally stable multiferroics and spintronic applications.
[Samples & Tests]
The article characterizes the magnetoelectric effect of the material using a lock-in amplifier and prepares a capacitor structure with a platinum top electrode in order to evaluate the magnetoelectric effect with a homemade instrument at room temperature.
Fig. 1 During data acquisition, an electromagnet (SB-175, 2.0T) generated a DC biased magnetic field (Hdc) of up to 5000 Oe. A Gaussmeter (REF-1205) aided in real-time monitoring . A current source (BKT-150V65A) provided sinusoidal AC current for generating an alternating magnetic field (Hac = 3 Oe, f = 1-2000 Hz). Both AC and DC magnetic fields were applied parallel to the surface of the multiferroic specimen. The induced ME voltage was recorded using a lock-in amplifier (OE1022).
Fig. 2PFT(X) (X= 0.02, 0.03, 0.05) Magneto-electric (ME) coupling effects of the samples are manifested in the magnetic field dependence of the transverse ME coefficient (αE31), which was measured by a dynamic phase-locking technique with a low alternating field (Hac) superimposed on a 1 kHz dc magnet (Hdc).
This approach has been widely used to study multiferroic composites whose ME behavior is thought to be mediated by macroscopic magnetostrictive and piezoelectric interactions, bridged by strain at the interface. In Fig. 2c, αE31 increases rapidly with Hdc until 1000 Oe and then rises slowly without reaching saturation. For the PFT(0.05), αE31 is measured to be 245 mV cm-1 Oe-1 when Hdc reaches 5000 Oe. In particular, the value of αE31 increases with increasing Fe concentration for a given Hdc condition, which should be attributed to the increase in seepage in the Fe network and the enhanced lattice coupling between ferroelectricity and magnetic response.
[Summary]
This paper has designed a series of single-phase multiferroics that can be magnetically ordered at 500 K and even higher temperatures by incorporating atomically occupied dn elements into the B-sites of the chalcogenide oxides. The homogeneous penetration of the iron-based sublattice into the polar substrate yields coupled long-range spin ordering as well as bistable and switchable ferroelectricity. More importantly, the apparent magnetoelectric response at room temperature is evaluated by performing dynamic phase-locking measurements. The article concludes that the integration of high-temperature magnetic ordering, nonvolatile ferroelectricity, and strong ME coupling into this family of PFTs will greatly facilitate the realization of multiferroics for practical applications.
[References]
