Magnetic phase transitions and magnetic entropy in the XY antiferromagnetic pyrochlores (Er1−xYx)2Ti2O7

We present the results of experimental determination of the heat capacity of the pyrochlore Er2Ti2O7 as a function of temperature (0.35–300 K) and magnetic field (up to 9 T), and for magnetically diluted solid solutions of the general formula (Er1−xYx)2Ti2O7 (x≤0.471). On either doping or increase of magnetic field, or both, the Néel temperature first shifts to lower temperature until a critical point above which there is no well-defined transition but a Schottky-like anomaly associated with the splitting of the ground state Kramers doublet. By taking into account details of the lattice contribution to the heat capacity, we accurately isolate the magnetic contribution to the heat capacity and hence to the entropy. For pure Er2Ti2O7 and for (Er1−xYx)2Ti2O7, the magnetic entropy as a function of temperature evolves with two plateaus: the first at Rln⁡2, and the other at Rln⁡16. When a very high magnetic field is applied, the first plateau is washed out. The influence of dilution at low values is similar to the increase of magnetic field, as we show by examination of the critical temperature versus critical field curve in reduced terms.

[1]  J. Copley,et al.  Order by disorder spin wave gap in the XY pyrochlore magnet Er2Ti2O7. , 2014, Physical review letters.

[2]  J. Oitmaa,et al.  Phase Transition and Thermal Order-by-Disorder in the Pyrochlore Quantum Antiferromagnet Er2Ti2O7: A High-Temperature Series Expansion Study , 2013, 1305.2935.

[3]  E. Ressouche,et al.  Magnetic order, magnetic correlations, and spin dynamics in the pyrochlore antiferromagnet Er2Ti2O7 , 2012, 1209.6153.

[4]  C. A. Whitman,et al.  Thermal conductivity of (Er1−xYx)2Ti2O7pyrochlore oxide solid solutions , 2012 .

[5]  A. Yaouanc,et al.  Crystal electric field in the R2Ti2O7 pyrochlore compounds , 2012, Journal of physics. Condensed matter : an Institute of Physics journal.

[6]  L. Balents,et al.  Order by quantum disorder in Er2Ti2O7. , 2012, Physical review letters.

[7]  R. Moessner,et al.  Quantum order by disorder and accidental soft mode in Er2Ti2O7. , 2012, Physical review letters.

[8]  A. Revcolevschi,et al.  High-pressure synchrotron X-ray diffraction study of the pyrochlores: Ho2Ti2O7, Y2Ti2O7 and Tb2Ti2O7 , 2011 .

[9]  M. Lees,et al.  Magnetic excitations in the XY-pyrochlore antiferromagnet Er$_2$Ti$_2$O$_7$ , 2010, 1006.2238.

[10]  E. Cordoncillo,et al.  Structural and Spectroscopic Study of a New Pink Chromium‐Free Er2(Ti,Zr)2O7 Ceramic Pigment , 2009 .

[11]  M. Gingras,et al.  Magnetic Pyrochlore Oxides , 2009, 0906.3661.

[12]  S. Saha,et al.  Low-temperature and high-pressure Raman and X-ray studies of pyrochlore Tb 2 Ti 2 O 7 : phonon anomalies and possible phase transition , 2009, 0904.3630.

[13]  Michel B. Johnson,et al.  Thermal properties of the pyrochlore, Y2Ti2O7 , 2009 .

[14]  M. White,et al.  Spin waves and quantum criticality in the frustrated XY pyrochlore antiferromagnet Er2Ti2O7. , 2008, Physical review letters.

[15]  Andrew S. Wills,et al.  Magnetic ordering in the XY pyrochlore antiferromagnet Er2Ti2O7: a spherical neutron polarimetry study , 2007 .

[16]  K. Rule,et al.  Structural Fluctuations in the spin-liquid state of Tb2Ti2O7. , 2007, Physical review letters.

[17]  Mary Anne White,et al.  Recommendations for accurate heat capacity measurements using a Quantum Design physical property measurement system , 2007 .

[18]  J. L. Smith,et al.  Critical examination of heat capacity measurements made on a Quantum Design physical property measurement system , 2003 .

[19]  E. Čižmár,et al.  Er2Ti2O7: Evidence of Order by Disorder in a Frustrated Antiferromagnet , 2001, cond-mat/0112007.

[20]  J. Gardner,et al.  Single crystal growth by the floating-zone method of a geometrically frustrated pyrochlore antiferromagnet, Tb2Ti2O7 , 1998 .

[21]  A. Burggraaf,et al.  Oxygen ion and mixed conductivity in compounds with the fluorite and pyrochlore structure , 1983 .

[22]  R. D. Shannon.  Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides , 1976 .

[23]  H. Blöte,et al.  Heat-capacity measurements on rare-earth double oxides R2M2O7 , 1969 .

[24]  O. Knop,et al.  DETERMINATION OF THE CRYSTAL STRUCTURE OF ERBIUM TITANATE, Er2Ti2O7, BY X-RAY AND NEUTRON DIFFRACTION , 1965 .

[25]  H. Da̧bkowska,et al.  Crystal Growth of Oxides by Optical Floating Zone Technique , 2010 .

[26]  M. Ma̧czka,et al.  Temperature-dependent Raman scattering studies of the geometrically frustrated pyrochlores Dy 2 Ti 2 O 7 , , 2008 .

[27]  H. C. Gupta,et al.  Lattice dynamic investigation of the zone center wavenumbers of the cubic A2Ti2O7 pyrochlores , 2001 .

[28]  Jenn-Shyong Hwang,et al.  Measurement of heat capacity by fitting the whole temperature response of a heat-pulse calorimeter , 1997 .