Pressure-Induced Phase Transitions In Gadolinium Iron Borate

An understanding of spin crossover (SC) dynamics is relevant to understanding of a role or participation of SC in natural systems including lower Mantle minerals, heme proteins as well as from fundamental science of view. For example, pressure-induced electronic spin transitions of Fe2+ and Fe3+ iron occur in magnesiowustite, silicate perovskite and post-perovskite which are abundant minerals in the Earth's lower mantle [1-3]. Such a SC phenomenon has recently been observed in a number of magnetic minerals FeBO3 [4, 5], BiFeO3 [6], Fe2O3 [7], and Y3Fe5O12 [8], (La, Pr)FeO3 [9, 10]. In those cases, iron ions are in the trivalent state Fe3+ and the high-spin-low-spin (HS-LS) crossover is manifested as the collapse of the local magnetic moment and as the transition of the antiferromagnet to a paramagnetic state. For example, in FeBO3 at low temperatures a spin-crossover and some magnetic transitions with two triple points were found [4, 5]. Gadolinium iron borate, GdFe3(BO3)4 is also a system with SEC and recently, we have reported on phase transitions induced by high pressures in this material [11, 12]. We studied the structural and magnetic behavior of GdFe573(BO3)4 at high pressures and temperatures using a diamond anvil cell and a Synchrotron Mossbauer Spectroscopy technique. The hyperfine parameters and results obtained from the experiments are discussed. Based on our experimental data and theoretical calculation a tentative magnetic P-T phase diagram and an equation of states of GdFe573(BO3)4 are proposed. Important features of the phase diagram are a spin crossover, insulator-semiconductor transition and possible presence of two triple points where magnetic and paramagnetic phases of the high-spin and low-spin states coexist. 1. J. Badro, J.-P. Rueff, G. Vankó, et al., Science 305, 383 (2004). 2. J. M. Jackson, W. Sturhahn, G. Shen, et al., American Mineralogist 90, 199 (2005). 3. J.Li, V.V. Struzhkin, H.-K. Mao, et al., PNAS 101, 14027 (2004). 4. I.A. Troyan, A. G. Gavrilyuk, et al., JETP Lett. 74, 24 (2001). 5. A.G. Gavriliuk, I.A. Trojan. et al., JETP 100, 688 (2005). 6. A.G. Gavriliuk, V.V. Struzhkin, et al., JETP Lett. 82, 224 (2005). 7. M.P. Pasternak, G.Kh. Rozenberg, et al., Phys. Rev. Lett. 82, 4663 (1999). 8. I.S. Lyubutin, A.G. Gavrilyuk, I. A. Troyan, et al., JETP Lett. 82, 702 (2005). 9. G.R. Hearne, M.P. Pasternak, et al., Phys. Rev. B 51, 11 495 (1995). 10. W.M. Xu, O. Naaman, G.Kh. Rozenberg, et al., Phys. Rev. B 64, 094411 (2001). 11. A.G. Gavriliuk, SA. Kharlamova, et al., JETP Lett. 80, 426 (2004). 12. A.G. Gavriliuk, S.A. Kharlamova, et al. J. Phys.: Condens. Matt. 17. 1-6 (2005)