Coupled ferroelectric polarization and magnetization in spinel FeCr2S4

Abstract

One of the core issues for multiferroicity is the strongly coupled ferroelectric polarization and magnetization, while so far most multiferroics have antiferromagnetic order with nearly zero magnetization. Magnetic spinel compounds with ferrimagnetic order may be alternative candidates offering large magnetization when ferroelectricity can be activated simultaneously. In this work, we investigate the ferroelectricity and magnetism of spinel FeCr2S4 in which the Fe2+ sublattice and Cr3+ sublattice are coupled in antiparallel alignment. Well defined ferroelectric transitions below the Fe2+ orbital ordering termperature Too = 8.5 K are demonstrated. The ferroelectric polarization has two components. One component arises mainly from the noncollinear conical spin order associated with the spin-orbit coupling, which is thus magnetic field sensitive. The other is probably attributed to the Jahn-Teller distortion induced lattice symmetry breaking, occuring below the orbital ordering of Fe2+. Furthermore, the coupled ferroelectric polarization and magnetization in response to magnetic field are observed. The present work suggests that spinel FeCr2S4 is a multiferroic offering both ferroelectricity and ferrimagnetism with large net magnetization.

Thermally assisted and magnetic field driven isostructural distortion of spinel structure and occurrence of polar order inCoCr2S4

“…Importantly, the value of P is ∼60 times larger than that of the value for the oxide counterpart CCO [7]. Moreover, the magnitude of P provides the second-highest value in the reported Cr spinels [14][15][16][17][18]. The polarization measured in H is shown in Fig.…”

“…Thus, the emergence of ferroelectricity must involve a crucial role of magnetic order and CCS is probably an improper ferroelectric material. So far improper ferroelectricities in spinel oxides and sulphides have been proposed either due to spiral spin order as observed in CCO [7,8], MnCr 2 O 4 [5], HgCr 2 S 4 [14], and FeCr 2 S 4 [15], or due to collinear magnetic structure having significant magnetostriction as also reported in NiCr 2 O 4 and FeCr 2 O 4 [6,10]. In the case of multiferroic NiCr 2 O 4 and FeCr 2 S 4 the magnetostriction engages structural transition to the lower crystal symmetry [10].…”

“…The value of P is appreciably larger than the enhanced P value due to A-site [11] as well as B-site [29] doping in CCO. Incidentally, the value of electric polarization with P ∼122 μC/m 2 at 15 K for 4 kV/cm poling field is the largest in ferroelectric spinels [14][15][16][17][18], except for CdCr 2 S 4 [12]. The magnetic field dependent P reveals significant magnetoelectric coupling while the magnetodielectric response scales linearly to the squared magnetization below ∼10 kOe as described by the Ginzburg-Landau theory.…”

“…Coexistence of colossal magnetocapacitance and magnetoresistance associated with the ferroelectricity, as observed from the hysteretic polarization (P -E) loop, has been reported in HgCr 2 S 4 , although ferroelectricity could not be detected from the pyroelectric current measurements [14]. Recently, reasonably large ferroelectricity was reported in FeCr 2 S 4 [15]. Interestingly, the ferroelectricity had two components, which were attributed to the noncollinear conical spin order and Jahn-Teller distortion as induced by the lattice symmetry breaking.…”

Experimental observation of magnetoelectricity in spin ice Dy2Ti2O7

“…During this process, the background of electrical current was reduced to the minimum level (i.e., <0.5 pA). The P was obtained by integrating the pyroelectric current (I) through warming the sample at 2 K min −1 ∼6 K min −1 , using a Keithley 6514 electrometer connected to PPMS [35]. This data was taken from the measurements at a rate of 2 K min −1 , implying a time scale of 14 min from 2 K to 30 K. For the pyroelectric current measurement under a constant magnetic field (H), the assigned field H was applied to the sample at T=2 K before the short-circuiting process until the end of the measurements at the rate of 2 K min −1 .…”