Magnetic field effect and dielectric anomalies at the spin reorientation phase transition ofGdFe3(BO3)4

Abstract

GdFe 3 ͑BO 3 ͒ 4 exhibits a structural phase transition at 156 K, antiferromagnetic order of the Fe 3+ moments at 36 K, followed by a spin reorientation phase transition at 9 K. The reorientation phase transition is studied through dielectric, magnetic, and heat capacity measurements under the application of external magnetic fields of up to 7 kOe. The dielectric constant indicates the existence of two distinct anomalies at T SR = 9 K that separate in temperature under external magnetic fields. The spin rotation phase transition is proven to be of the first-order nature through the magnetic analog of the Clausius-Clapeyron equation. Magnetodielectric effect of up to 1% is observed at 8 K and 7 kOe. The uniaxial magnetocaloric effect along the c axis is observed below the spin reorientation phase transition of 9 K. GdFe 3 ͑BO 3 ͒ 4 belongs to the trigonal system with space group R32. It is similar to huntite CaMg 3 ͑CO 3 ͒ 4 , a trigonal trapezohedral structure that is one of the five trigonal types. Borate crystals of this category are appealing because of their possible applications as single crystal minilasers due to their good luminescent and nonlinear optical properties. In particular for GdFe 3 ͑BO 3 ͒ 4 single crystals, recent studies have focused on the better understanding of its optical properties, and at the same time on its magnetic properties through phase matching of absorption and second harmonic generation spectra. 1,2 The magnetic properties of the rareearth iron borates are also of fundamental interest because of the existence and mutual interference of two magnetic subsystems ͑Fe and Gd͒. The understanding of the magnetic orders of the gadolinium and iron sublattices, and the coupling between the iron spins and the gadolinium moments that contributes to the crystal's rich magnetic properties is of fundamental importance.The crystal structure of huntite has been analyzed and described elsewhere, 3-5 it consists of GdO 6 bipyramids and FeO 6 octahedrons. The octahedrons form threefold helicoidal chains along the c axis. The bipyramids are located between three nearly equal distant octahedrons. Rare-earth iron borates, RFe 3 ͑BO 3 ͒ 4 ͑R =Eu to Ho, and Y͒, undergo a structural transition at higher temperatures and an antiferromagnetic ͑AFM͒ transition involving the Fe spins at T N Ϸ 35 K. 6 For R = Gd a weakly first-order structural phase transition at T 1 = 156 K changes the structural symmetry from R32 to P3 1 2 1 . 5 A second-order phase transition at T N = 36 K results in the AFM ordering of the Fe 3+ magnetic moments aligned in the basal plane. At T SR = 9 K, another sharp phase transition occurs characterized by a spin reorientation of the Fe 3+ magnetic moments by 90°from the basal plane to the c axis.The coupling between the Gd moments and the Fe spins at low temperatures is strong in GdFe 3 ͑BO 3 ͒ 4 and it was speculated that the reorientation of the AFM iron spin system is triggered by the anisotropy of the Gd moments aligned with the c axis. 6 This exchange interaction is indirect and ...

Magnetodielectric and magnetoelastic coupling inTbFe3(BO3)4

“…For GdFe 3 ͑BO 3 ͒ 4 , the upturn was suggested to originate from the polarization of Gd spins and the vicinity of a spin-reorientation transition. 16 In contrast, there is no spin-reorientation in TbFe 3 ͑BO 3 ͒ 4 but as well the specific heat as the magnetization data exhibit a broad Schottky-type anomaly at the temperature where there is the peak in ⑀ ab . Recently, the anomalies of the specific heat and the magnetization were explained in terms of temperature-driven population of the ground state of Tb ion split by the internal field of Fe spins 8 which suggests a similar, i.e., Schottky type, scenario for the broad peak in ⑀ ab .…”

“…Interestingly, despite the fact that in GdFe 3 ͑BO 3 ͒ 4 the magnetic structure in the ordered phase is different compared to TbFe 3 ͑BO 3 ͒ 4 , the anomaly at T N as well as the lowtemperature behavior ⑀ c ͑T͒ and ⑀ ab ͑T͒ is roughly similar in both compounds. 16 In particular, both materials exhibit an increase in ⑀ ab below T N which in GdFe 3 ͑BO 3 ͒ 4 is truncated by a spin-reorientation transition. For GdFe 3 ͑BO 3 ͒ 4 , the upturn was suggested to originate from the polarization of Gd spins and the vicinity of a spin-reorientation transition.…”

“…In the magnetically ordered phase Gd 4f-Fe 3d magnetic interactions cause a spinreorientation transition which is coupled to the dielectric constant via spin-lattice interaction. 7,16 Application of magnetic field strongly shifts the spin-reorientation transition, giving rise to 1% magnetodielectric effect. 16 Here, we present a detailed experimental study on the magnetodielectric and magnetoelastic coupling in TbFe 3 ͑BO 3 ͒ 4 .…”

“…7,16 Application of magnetic field strongly shifts the spin-reorientation transition, giving rise to 1% magnetodielectric effect. 16 Here, we present a detailed experimental study on the magnetodielectric and magnetoelastic coupling in TbFe 3 ͑BO 3 ͒ 4 . We have measured the dielectric constant and the magnetostriction and we show by analysis of Raman spectroscopy data that the magnetodielectric coupling is mediated by strain and caused by shifts in the corresponding transverse optical ͑TO͒-phonon modes via Lyddane-Sachs-Teller ͑LST͒ relationship.…”

Ho and Fe magnetic ordering in multiferroic HoFe3(BO3)4

“…2,3 However, recent observations of improper ferroelectricity, 4,5 anomalous even within the realm of magnetoelectricity, require an even better understanding of the subject. Rare earth iron borates RFe 3 (BO 3 ) 4 , where R = rare earth, [6][7][8][9] are multiferroics, characterized by long-range magnetic wave vectors q c*, [10][11][12][13][14][15] and show a large magnetoelectric effect ( P ∼ 100 μC m −2 ). The RFe 3 (BO 3 ) 4 crystal structure 16,17 allows a dominant Fe-Fe exchange interaction, which is reflected by a T N in a narrow temperature range (30-40 K) for compounds with different R. The rare earth exchange interaction takes place via O and B, i.e., R-O-B-O-R.…”