Weak ferromagnetism and ferroelectricity in K3Fe5F15

Abstract

Here, we report on the observation of a weak ferromagnetic transition at TN=122K in a K3Fe5F15 system which is ferroelectric and ferroelastic below Tc=490K. The magnetization and the susceptibility continuously increase with decreasing T down to 2K. The Mössbauer spectra show a spontaneous magnetic ordering and at least three sites corresponding to Fe2+ and Fe3+. The ratio between Fe2+ and Fe3+ is 60:40. At 6K, there are two magnetically ordered sextets with internal fields of 585 and 263kOe. The “slim” hysteresis loops observed are as well characteristic of weak ferromagnetism. At 122K and at low frequencies, the system shows dielectric anomaly characteristic of magnetoelectric behavior.

Phase transitions in fluoride KFe 2 F 6 with tetragonal tungsten bronze structure

“…1(c)) and, thus, full magnetic entropy is about $13 J/mol K. But even this value is much less than maximum magnetic entropy DS = Rln(6) + Rln(5) = 28 J/mol K for Fe 2+ and Fe 3+ ions which are in high-spin states (Fe 3+ : I = 5/2, Fe 2+ : I = 2) according to Mö ssbauer data [11].…”

Physics and Applications of Bismuth Ferrite

“…[37] BaMnF 4 , for example, is the earliest known example of a material with spin canting induced by ferroelectricity, [28] the physics being the same as in the ferroelectrically induced local spin canting in BiFeO 3 , discussed later in this Review. K 3 Fe 5 F 15 [38][39][40] is a ferroelectric ferrimagnet with 2 Fe þ3 ions and 3 Fe þ2 ions per unit cell, adding to a weak net ferromagnetic moment. A particularly interesting multiferroic is Sr 3 (FeF 6 ) 2 , which merits further study.…”

Muon spin relaxation in some multiferroic fluorides

“…10 The SR measurements were performed on the SR general purpose system facility at the Paul Scherer Institute, Switzerland. The bulk dc magnetic measurements were performed on the Quantum Design MPMS-XL-5 SQUID magnetometer in the external field of 1 kOe between 2 and 400 K. The X-band continuous wave EPR measurements were carried out on the commercial Bruker E580 spectrometer using a TE102 dual cavity and an Oxford cryogenics continuous flow E900 cryostat.…”

“…They are performed on newly synthesized samples and are similar but not identical to the results previously published. [10][11][12] In K 3 Fe 5 F 15 ͑Ref. 10͒ a sharp first-order antiferromagnetic transition takes place at T N = 125 K. Simultaneously, a splitting between field-cooled ͑FC͒ and zerofield-cooled ͑ZFC͒ susceptibility data occurs, which suggests that the system is a magnetic relaxor ͓Fig.…”

“…According to bulk susceptibility measurements, all systems exhibit at least two magnetic phase transitions. [10][11][12] The local magnetic structure of the above-mentioned fluorides is still not clear. Here we investigate this issue from a local insight by means of the muon spin relaxation ͑SR͒ technique.…”