Construction of Magnetoelectric Composites with a Large Room‐Temperature Magnetoelectric Response through Molecular–Ionic Ferroelectrics

Abstract

Magnetoelectric materials with a large magnetoelectric response, a low operating magnetic (or electric) field, and a room‐temperature (or higher) operating temperature are of key importance for practical applications. However, such materials are extremely rare because a large magnetoelectric response often requires strong coupling between spins and electric dipoles. Herein, an example of a magnetoelectric composite is prepared by using a room‐temperature multiaxial molecular–ionic ferroelectric, tetramethylammonium tetrachlorogallate(III) (1). Investigation of the magnetoelectric effect of the magnetoelectric laminate composite indicates that its room‐temperature magnetoelectric voltage coefficient (αME) is as high as 186 mV cm−1 Oe−1 at HDC = 275 Oe and at the HAC frequency of ≈39 kHz, providing a valid approach for the preparation of magnetoelectric materials and adding a new member to the magnetoelectric material family.

Room‐Temperature Magnetoelectric Response in Molecular–Ionic Ferroelectric‐Based Magnetoelectric Composites

“…As demonstrated previously that the ferroelectricity of [N(CH 3 ) 4 ][GaCl 4 ] originates from the displacement between the anion and cation, the enhancement in polarization of 1 is thus attributed to the dipole moment of the [GaBrCl 3 ] − anion itself ( μ = 1.667 Debye; based on the MP2/6‐311+G(d,p) calculations; Figure b) [6a,7]. Indeed, when the dipole moment of [GaBr 3 Cl] − anion was not considered, the calculated polarization value of 1 is the same as that of [N(CH 3 ) 4 ][GaCl 4 ] (4.37 μC cm −2 , Figure c and Table S3, Supporting Information) …”

“…The ratio of Br to Cl in 1 was determined by energy‐dispersive X‐ray spectroscopy (EDX), which indicated that the ratio of Br to Cl was 1:3 (Table S1, Supporting Information). The powder X‐ray diffraction (PXRD) measurement of 1 showed that its PXRD peaks were very similar to those observed in the ferroelectric [N(CH 3 ) 4 ][GaCl 4 ] (Figure a), suggesting that 1 probably crystallizes in the polar Amm 2 space group and may be a room‐temperature ferroelectric. Consistently, the single‐crystal determination demonstrated that 1 indeed crystallizes in the Amm 2 space group (Figure S1 and Table S2, Supporting Information).…”

“…[N(CH 3 ) 4 ][GaCl 4 ] was prepared based on the previous literature . [N(CH 3 ) 4 ][GaBrCl 3 ] ( 1 ) was synthesized by the dissolving gallium(III) chloride (5 mmol) and tetramethylammonium bromide (5 mmol) in a methanol solution under stirring.…”

“…In the previous work, we have demonstrated for the first time that the multiaxial molecular–ionic ferroelectric is an excellent candidate for the construction of magnetoelectric composites . Although the magnetoelectric coefficient for the obtained magnetoelectric composite of Terfenol‐D/[N(CH 3 ) 4 ][GaCl 4 ] is above 0.186 V cm −1 Oe −1 at an alternating magnetic field ( H AC ) frequency of ≈39 kHz at room temperature, this value remains far from that of the giant magnetoelectric response.…”

“…Although the magnetoelectric coefficient for the obtained magnetoelectric composite of Terfenol‐D/[N(CH 3 ) 4 ][GaCl 4 ] is above 0.186 V cm −1 Oe −1 at an alternating magnetic field ( H AC ) frequency of ≈39 kHz at room temperature, this value remains far from that of the giant magnetoelectric response. Due to the magnetoelectric response in magnetoelectric composites being related to not only the piezoelectricity of the ferroelectric material but also to the piezomagnetic coefficient of the ferromagnetic phase, when we use the multiaxial molecular–ionic ferroelectric [N(CH 3 ) 4 ][GaCl 3 Br] ( 1 ) as the ferroelectric component and amorphous FeBSi alloy (Metglas; Advanced Technology & Materials Co., Ltd.) as the ferromagnetic material to prepare the magnetoelectric composite, it is expected that the magnetoelectric composite Metglas/[N(CH 3 ) 4 ][GaBrCl 3 ] (named Metglas/ 1 ) will exhibit a better magnetoelectric response than that of Terfenol‐D/[N(CH 3 ) 4 ][GaCl 4 ] . This conjecture is because 1) 1 is expected to exhibit a better ferroelectricity (piezoelectricity) than that reported previously for [N(CH 3 ) 4 ][GaCl 4 ], due to the ferroelectricity of 1 being generated not only from the displacements of the [N(CH 3 ) 4 ] + cations and the [GaCl 3 Br] − anions but also the dipole moment of the polar [GaBrCl 3 ] − anion; 2) compared with that of Terfenol‐D, Metglas exhibits a large effective piezomagnetic coefficient and low‐field saturation.…”