Magnetic Order in Superconductors

The effects of magnetic impurities and the possibility of magnetic ordering in superconductors has had a rich and interesting history, and we have had a longstanding interest in investigating such systems.  Magnetic impurities substituted into a superconductor were found to quickly suppress superconductivity due to the strong spin scattering that disrupts the Cooper pairs.  Typically ~1% substitution was enough to completely extinguish the superconducting state, and such a low concentration of magnetic moments precludes the possibility of cooperative magnetic states forming and competing with the superconducting order parameter.  The first exception to this behavior was realized for the (Ce_1-x-R_x)Ru₂ system, where over 30% of non-magnetic Ce⁴⁺ could be replaced by the magnetic heavy lanthanides before superconductivity was suppressed.  Strong ferromagnetic correlations were found to develop in the superconducting state, but no long range order was present.

            The first examples of true long range magnetic order coexisting with superconductivity were provided by the ternary Chevrel-phase superconductors (RMo₆S₈) and related (RRh₄B₄) compounds.  In these materials there is a separate, fully occupied lanthanide sublattice.  The fact that these materials were superconducting at all implied that the magnetic ions and the superconducting electrons belonged to different, "isolated", sublattices, and thereby the conventional Abrikosov-Gorkov spin-depairing mechanism was suppressed.  The magnetic ordering temperatures are all low, ~1K, and thus it was argued that electromagnetic (dipolar) interactions should dominate the energetics of the magnetic system.  For materials where these interactions favor antiferromagnetism the magnetization averages to zero on the length scale of a unit cell (a), which results in a weak influence on the superconducting state (a<<x,l).  This is the most prevalent case found in nature, and apart from a few anomalies in properties such as the upper critical field, the antiferromagnetic order and superconductivity were found to readily accommodate one another.  In the rare and more interesting situation where the magnetic interactions are ferromagnetic, there is strong coupling to the superconducting state that originates from the internally generated magnetic field.  The competition with the superconducting order parameter gives rise to long wavelength oscillatory magnetic states and/or reentrant superconductivity.  The studies of these materials contributed greatly to our understanding of these two competing phenomena, but the possible role of exchange interactions in these systems, and the related question of how the dipolar interaction alone could be responsible for the antiferromagnetism in some materials while others (with the same crystal structure) are ferromagnets, remained unexplained.

            The cuprate superconductors offer new and interesting perspectives into our understanding of "magnetic superconductors" for a number of reasons.  In the materials typified by RBa₂Cu₃O_6+x (1-2-3) and R₂Ba₄Cu₈O₁₆ (2-4-8), for example, the R ions appear to be electronically isolated from the Cu-O layers where the Cooper pairs form, similar to the ternary superconductors, and the low lanthanide ordering temperatures (~1 K) suggested that the cuprate superconductors were again prototypical "magnetic superconductors".  They were also interesting because the layered crystal structure, with c ~3a, rendered them naturally two-dimensional (2d) in nature, and indeed some of the best 2d magnets known belong to this class of materials.  However, there are also examples where the magnetic ordering temperature is much too high to be explained by dipolar interactions, and it has become clear that R-R exchange interactions actually must play a dominant role in the magnetism, as is also clearly the case for the new RNi₂B₂C class of superconductors.  In contrast to the ternary superconductors, in the cuprates there is no clear separation of the lanthanide sublattice from the superconducting electrons.  Moreover, one of the most interesting aspects of the cuprates concerns the magnetism associated with the Cu ions, which is the same sublattice where the superconducting pairing occurs.  The undoped cuprates are antiferromagnetic insulators where the S=1/2 Cu spins order at high temperatures, typically near or above room temperature.  The in-plane Cu exchange interactions are much stronger than along the c-axis, and thus again the magnetism is two-dimensional in nature.  With doping, the materials lose the Cu long range magnetic order and become high T_C superconductors.  However, the Cu moments and energetics are still present.

            For the lanthanide magnetism, the overall behavior is quite different.  In the single-layer R₂CuO₄ type materials the lanthanide exchange interactions are three dimensional in nature, and typically the Cu and R systems exhibit relatively strong coupling.  For the multi-layered materials, on the other hand, the distance along the stacking axis becomes quite large, and this physical separation renders the ordering two-dimensional in nature, but for very different reasons than for the Cu system.  The R-Cu interactions also tend to be weaker and the lanthanide sublattice appears to be relatively isolated from the rest of the system, making them prototypical 2d magnets with low ordering temperatures.

            In all of these systems, for both the Cu magnetic order as well as the lanthanide magnetic order, the spin structures are relatively simple commensurate antiferromagnetic configurations.  In particular, no materials have been discovered yet that exhibit a net ferromagnetic component, with its associated macroscopic magnetization.  By commensurate we mean that the antiferromagnetic unit cell is a simple integer multiple of the chemical unit cell.  Within the Cu-O planes, for example, the nearest-neighbor spins have always been found to be antiparallel, and the spins always point along a common direction (i.e., they are collinear) within the a-b plane.  However, there can be the complication that some of the structures are noncollinear, by which we mean that the direction of the spins between the layers is not necessarily along the same crystallographic direction.  The added complication of having both Cu and R moments can then make the magnetism of these cuprates quite rich and interesting.

    In the following example we have rare earth ordering at low T, Ru magnetic ordering at quite high T, and coexistence of both types of long range antiferromagnetic order with superconductivity.

The figure on the left shows the development of long range antiferromagnetic order of the Gd moments in this superconducting material.  This ordering occurs at low temperature and coexists with superconductivity, similar to many "magnetic superconductors" that have been investigated over the years (see list of publications below).  The figure on the right side demonstrates that the Ru ions also carry a magnetic moment, and they order antiferromagnetically as well.  This is the highest magnetic ordering temperature observed so far in a superconducting material.  Phys. Rev. B 61, R14964 (2000).

We have also recently carried out an investigation of the magnetic properties of the superconducting RuSr₂Eu_1.2Ce_0.8Cu₂O₁₀ system. In this case, however, the magnetic order that has been observed is associated with an impurity phase;  no magnetic order associated with the titled compound has been found so far (). 

        See the related topics

 Spin Dynamics in Electron-doped Cuprate Superconductors

Iron-based Superconductors

Some Examples of Magnetic Superconductor Publications:

Direct Observation of Long Range Ferromagnetic Order in the Reentrant Superconductor HoMo₆S₈, J. W. Lynn, D. E. Moncton, W. Thomlinson, G. Shirane and R. N. Shelton, Sol. St. Comm. 26, 493 (1978).

Neutron Diffraction Study of Magnetic Order in the Ternary Superconductor ErMo₆Se₈, J. W. Lynn, D. E. Moncton, G. Shirane, W. Thomlinson, J. Eckert and R. N. Shelton, J. Appl. Phys. 49, 1389 (1978).

Magnetic Properties of the Superconducting Alloy System (Ce_1-cHo_c)Ru₂:  A Neutron Scattering Study, J. W. Lynn and C. J. Glinka, J. Mag. and Mag. Materials 14, 179 (1979).

Magnetic Correlations and Crystal-Field Levels in the Superconductor (Ce_.73Ho_.27)Ru₂, J. W. Lynn, D. E. Moncton, L. Passell, and W. Thomlinson, Phys. Rev. B 21, 70 (1980).

Neutron Scattering Studies of Magnetic Superconductors, J. W. Lynn and R. N. Shelton, J. Mag. and Mag. Materials 18, 1577 (1980).

Competition Between Ferromagnetism and Superconductivity in HoMo₆S₈, J. W. Lynn, G. Shirane, W. Thomlinson and R. N. Shelton, Phys. Rev. Lett. 46, 368 (1981).

Observation of Long Range Oscillatory Magnetic Order in the Reentrant Superconductor HoMo₆S₈, J. W. Lynn, J. L. Ragazzoni, R. Pynn and J. Joffrin, J. de Physique Lettres 42, L45 (1981).

Neutron Scattering Studies of the Magnetic Superconductor (Ce_1-xTb_x)Ru₂, J. A. Fernandez-Baca and J. W. Lynn, J. Appl. Phys. 52, 2183 (1981).

Magnetic Properties of the Reentrant Ferromagnetic Superconductor HoMo₆S₈, J. W. Lynn, G. Shirane, W. Thomlinson, R. N. Shelton and D. E. Moncton, Phys. Rev. B 24, 3817 (1981).

Formation of an Oscillatory Magnetization Near the Reentrant Superconducting Transition in HoMo₆S₈, J. W. Lynn, R. Pynn, J. Joffrin, and J. L. Ragazzoni, Physica 108B, 801 (1981).

Evolution from Ferromagnetism to Spin Glass Behavior in Amorphous (Fe_1-xNi_x)_.75P_.16B_.06Al_.03, J. W. Lynn, R. W. Erwin, H. S. Chen and J. J. Rhyne, Solid State Commun. 46, 317 (1983).

Field Dependence of the Oscillatory Magnetic State in Superconducting HoMo₆S₈, J. W. Lynn, R. Pynn, J. L. Raggazoni, and J. Joffrin, J. Mag. Mag. Mater. 32, 493 (1983).

Investigation of the Magnetic and Superconducting Properties of (Er_1-xHo_x)Rh₄B₄, J. W. Lynn, R. N. Shelton, H. E. Horng and C. J. Glinka, Physica 120B, 224 (1983).

Investigation of the Modulated Magnetic Phase of HoMo₆S₈, J. W. Lynn, R. Pynn, J. Joffrin, J. L. Ragazzoni and R. N. Shelton, Phys. Rev. B27, 581(RC) (1983).

Neutron Scattering Studies of Phase Transitions in Superconductors, J. W. Lynn, J. Less Comm. Metals 94, 75 (1983).

Magnetic Ordering in Superconductors, R. Pynn, J. W. Lynn and J. Joffrin, Helvetica Physica Acta 56, 179 (1983).

Temperature-Dependent Sinusoidal Magnetic Order in the Superconductor HoMo₆Se₈, J. W. Lynn, J. A. Gotaas, R. W. Erwin, R. A. Ferrell, J. K. Bhattacharjee, R. N. Shelton and P. Klavins, Phys. Rev. Lett. 52, 133 (1984).

Magnetic and Superconducting Properties of Holmium-Rich (Er_1-xHo_x)Rh₄B₄, J. W. Lynn, J. A. Gotaas, R. N. Shelton, H. E. Horng and C. J. Glinka, Phys. Rev. B31, 5756 (1985).

Magnetic Field Dependence of the Small-Angle Neutron Scattering in HoMo₆Se₈, J. A. Gotaas and J. W. Lynn, J. Mag. Mag. Matr. 54-57, 1529 (1986).

Magnetic Fluctuations and Two-Dimensional Ordering in ErBa₂Cu₃O₇, J. W. Lynn, W.-H. Li, Q. Li, H. C. Ku, H. D. Yang and R. N. Shelton, Phys. Rev. B 36, 2374(RC) (1987).

Suppression of Superconductivity by Antiferromagnetism in Tm₂Fe₃Si₅, J. A. Gotaas, J. W. Lynn, R. N. Shelton, P. Klavins, and H. F. Braun, Phys. Rev. B36, 7277 (RC) (1987).

Absolute Measurement of the Ordered Magnetic Moment in Holmium Rich (Er_1-xHo_x)Rh₄B₄, Q. Li, J. W. Lynn and J. A. Gotaas, Phys. Rev. B35, 5008 (1987).

Antiferromagnetic Structure of the Cubic Superconductor ErPd₂Sn, H. B. Stanley, J. W. Lynn, R. N. Shelton and P. Klavins, J. Appl. Phys. 61, 3371 (1987).

Effects of Crystal Anisotropy on Magnetization and Magnetic Order in Superconducting RBa₂Cu₃O_7-x, R. N. Shelton, R. W. McCallum, M. A. Damento, K. A. Gschneidner, Jr., H. C. Ku, H. D. Yang, J. W. Lynn, W-H. Li, and Q. Li, Physica 148B, 285 (1987).

Two-Dimensional Character of the Magnetic Order in ErBa₂Cu₃O₇, J. W. Lynn, W-H. Li, Q. Li, H. C. Ku, H. D. Yang and R. N. Shelton, Rev. Sol. St. Phys. 1, 357 (1987).

Nature of the Magnetic Order of Cu in Oxygen Deficient RBa₂Cu₃O_6+x, J. W. Lynn, W-H. Li, H. A. Mook, B. C. Sales, and Z. Fisk, Phys. Rev. Lett. 60, 2781 (1988).

Antiferromagnetic Order of the Cu in RBa₂Cu₃O_6+x, J. W. Lynn, W-H. Li, H. A. Mook, B. C. Sales and Z. Fisk, J. de Physique 49, C8-1, 2153 (1988).

Antiferromagnetic Structure and Crystal Field Splittings in the Cubic Heusler Alloys HoPd₂Sn and ErPd2Sn, W-H. Li, J. W. Lynn, H. B. Stanley, T. J. Udovic, R. N. Shelton and P. Klavins, J. de Physique 49, C8-1, 373 (1988).

Long Range Antiferromagnetic Order of the Cu in Oxygen-Deficient, RBa₂Cu₃O_6+x, W-H. Li, J. W. Lynn, H. A. Mook, B. C. Sales and Z. Fisk, Phys. Rev. B37, 9844 (RC) (1988).

Magnetic Order in RBa₂Cu₃O_6+x, J. W. Lynn and W-H. Li, J. Appl. Phys. 64, 6065 (1988).

Magnetic Order of Pr in PrBa₂Cu₃O₇, W-H. Li, J. W. Lynn, S. Skanthakumar, T. W. Clinton, A. Kebede, C.-S. Jee, J. E. Crow, and T. Mihalisin, Phys. Rev. B 40, 5300 (1989).

Pressure Dependence of the Cu Magnetic Order in NdBa₂Cu₃O_6+x, J. W. Lynn, W-H. Li, S. F. Trevino and Z. Fisk, Phys. Rev. B40, 5172 (1989).

Magnetic Phase Transitions and Structural Distortion in Nd₂CuO₄, S. Skanthakumar, H. Zhang, T. W. Clinton, W-H. Li, J. W. Lynn, Z. Fisk, and S-W. Cheong, Physica C 160, 124 (1989).

2-D and 3-D Magnetic Behavior of Er in ErBa₂Cu₃O₇, J. W. Lynn, T. W. Clinton, W-H. Li, R. W. Erwin, J. Z. Liu, K. Vandervoort, R. N. Shelton and P. Klavins, Phys. Rev. Lett. 63, 2606 (1989).

Antiferromagnetic Ordering in Superconducting and Oxygen-Deficient non-Superconducting RBa₂Cu₃O_7-d Compounds (R = Nd and Sm), K. N. Yang, J. M. Ferreira, B. W. Lee, M. B. Maple, W-H. Li, J. W. Lynn, and R. W. Erwin, Phys Rev. B40, 10963 (1989).

Magnetic Ordering of Nd in (Nd-Ce)₂CuO₄, J. W. Lynn, S. Skanthakumar, I. W. Sumarlin, W-H. Li, R. N. Shelton, J. L. Peng, Z. Fisk, and S-W. Cheong, Phys. Rev. B 41, 2569 (1990).

Magnetic Order of the Cu Planes and Chains in NdBa₂Cu₃O_6+x, W-H. Li, J. W. Lynn, and Z. Fisk, Phys. Rev. B41, 4098 (1990).

Two-Dimensional Magnetic Order of Er in ErBa₂Cu₃O₇, J. W. Lynn, T. W. Clinton, W-H. Li, R. W. Erwin, J. Z. Liu, R. N. Shelton, and P. Klavins, J. Appl. Phys. 67, 4533 (1990).

Magnetic Order and Spin Fluctuations in Oxide Superconductors, J. W. Lynn, Physica B 163, 69 (1990).

Magnetic Phase Transitions in Nd₂CuO₄, S. Skanthakumar, H. Zhang, T. W. Clinton, I. W. Sumarlin, W-H. Li, J. W. Lynn, Z. Fisk, and S-W. Cheong, J. Appl. Phys. 67, 4530 (1990).

Magnetic Properties of Pr in PrBa₂Cu₃O₇, S. Skanthakumar, W-H. Li, J. W. Lynn, A. Kebede, J. E. Crow, and T. Mihalisin, Physica B 163, 239 (1990).

Two- and Three-Dimensional Magnetic Order of the Rare Earth Ions in RBa₂Cu₄O₈, H. Zhang, J. W. Lynn, W-H. Li, T. W. Clinton, and D. E. Morris, Phys. Rev. B41, 11229 (1990).

On the Crystal and Spin Structure of Nd₂CuO₄, S. Skanthakumar and J. W. Lynn, Physica C170, 175 (1990).

Magnetic Ordering of the Cu Spins in PrBa₂Cu₃O_6+x, N. Rosov, J. W. Lynn, G. Cao, J. W. O'Reilly, P. Pernambuco-Wise and J. E. Crow, Physica C 204, 171 (1992).

Magnetic Ordering of Sm in Sm₂CuO₄, I. W. Sumarlin, S. Skanthakumar, J. W. Lynn, J. L. Peng, W. Jiang, Z. Y. Li and R. L. Greene, Phys. Rev. Lett. 68, 2228 (1992).

Observation of Oscillatory Magnetic Order in the Reentrant Antiferromagnetic Superconductor HoNi₂B₂C, T. E. Grigereit, J. W. Lynn, Q. Huang, A. Santoro, R. J. Cava, J. J. Krajewski, and W. F. Peck, Jr., Phys. Rev. Lett. 73, 2756 (1994).

Magnetic Ordering and Crystallographic Structures in the Superconducting RNi₂B₂C Materials, J. W. Lynn, S. Skanthakumar, Q. Huang, S. K. Sinha, Z. Hossain, L. C. Gupta, R. Nagarajan, and C. Godart, Phys. Rev. B 55, 6584 (1997).

Antiferromagnetic Order of the Ru and Gd in Superconducting RuSr₂GdCu₂O₈, J. W. Lynn, B. Keimer, C. Ulrich, C. Bernhard, and J. L. Tallon, Phys. Rev. B 61, R14964 (2000).

Pr Magnetic Order and Spin Dynamics in Cuprates, J. W. Lynn, N. Rosov, S. N. Barilo, L. Kurnevitch, and A. Zhokhov, Chinese Journal of Physics 38, 286 (2000).

Direct Observation of Spontaneous Weak-Ferromagnetism in the Superconductor ErNi₂B₂C, S. -M. Choi, J. W. Lynn, D. Lopez, P. L. Gammel, P. C. Canfield and S. L. Bud'ko, Phys. Rev. Lett. 87, 107001 (2001).

Magnetic Order in YBa₂Cu₃O_6+x Superconductors, H. A. Mook, P. Dai, S. M. Hayden, A. Hiess, J. W. Lynn, S-H. Lee, and F. Dogan, Phys. Rev. B 66, 144513 (2002).

Antiferromagnetic Order as the Competing Ground State in Electron Doped Nd_1.85Ce_0.15CuO₄, H. J. Kang, P. Dai, J. W. Lynn, M. Matsuura, J. R. Thompson, S-C. Zhang, D. N. Argyriou, Y. Onose, and Y. Tokura, Nature 423, 522 (2003).

Reply to Comment on "Antiferromagnetic Order as the Competing Ground State in Electron-doped Nd_1.85Ce_0.15CuO₄", H. J. Kang, P. Dai, J. W. Lynn, M. Matsuura, J. E. Thompson, S-C Zhang, D. N. Argyriou, Y. Onose, and Y. Tokura, Nature 426, 140 (2003).

Effect of a Magnetic Field on the Long-range Magnetic Order in insulating Nd₂CuO₄ and superconducting Nd_1.85Ce_0.15CuO₄, M. Matsuura, P. Dai, H. J. Kang, J. W. Lynn, D. N. Argyriou, K. Prokes, Y. Onose, and Y. Tokura, Phys Rev. B 68, 144503 (2003).

"Spin-Flop" Transition and Anisotropic Magnetoresistance in Pr_1.3-xLa_0.7Ce_xCuO₄:  Unexpectedly Strong Spin-Charge Coupling in Electron-Doped Cuprates, A. N. Lavrov, H. J. Kang, Y. Kurita, T. Suzuki, S. Koniya, J. W. Lynn, S-H. Lee, P. Dai, and Y. Ando, Phys. Rev. Lett. 92, 227003 (2004).

Magnetic Field Effect on Static Antiferromagnetic Order Above the Upper Critical Field in Nd_1.85Ce_0.15CuO₄, M. Matsuura, P. Dai, H. J. Kang, J. W. Lynn, D. N. Argyriou, Y. Onose, and Y. Tokura, Phys Rev. B 69, 104510 (2004).

Electronic Inhomogeneity and Competing Phases in Electron-doped superconducting Pr_0.88LaCe_0.12CuO_4-x, H. J. Kang, P. Dai, H. A. Mook, M. Matsuura, J. W. Lynn, Y. Kurity, S. Komiya, and Y. Ando, Phys. Rev. B 71, 100502 (Rapid Communications) (2005).

Electronically Competing Phases and Their Magnetic Field Dependence in Electron-doped Nonsuperconducting and Superconducting Pr_1.88LaCe_0.12CuO_4+-d, H. J. Kang, P. Dai, H. A. Mook, D. N. Argyriou, V. Sikolenko, J. W. Lynn, Y. Kurita, S. Komiya, and Y. Ando, Phys. Rev. B 71, 214512 (2005).

Neutron Scattering Study of La_1.9Ca_1.1Cu₂O_6+d and La_1.85Sr_0.15CaCu₂O_6+d, M. Hucker, Y.-J. Kim, G. D. Gu, J. M. Tranquada, B. D. Gaulin, and J. W. Lynn, Phys. Rev. B 71, 094510 (2005).

Search for Magnetic Order in Superconducting RuSr₂Eu_1.2Ce_0.8Cu₂O₁₀, J. W. Lynn, Y. Chen, Q. Huang, S. K. Goh, and G. V. M. Williams, Phys. Rev. B 76, 014519 (2007).

Magnetic Order Close to Superconductivity in the Iron-based Layered La(O_1-xF_x)FeAs systems, C. de la Cruz, Q. Huang, J. W. Lynn, J. Li, W. Ratcliff II, J. L. Zarestky, H. A. Mook, G. F. Chen, J. L. Luo, N. L. Wang, and P. Dai, P. Dai, Nature 453, 899 (2008).  Supplementary Material.

Magnetic Order of the Iron Spins in NdOFeAs, Y. Chen, J. W. Lynn, G. F. Chen, G. Li, Z. C. Li, J. L. Luo, N. L. Wang, P. Dai, C. dela Cruz, and H. A. Mook Phys. Rev. B 78, 064515 (2008).

Intrinsic Properties of Stoichiometric LaOFeP, T. M. McQueen, M. Regulacio, A. J. Williams, Q. Huang, J. W. Lynn, Y. S. Hor, D.V. West, and R. J. Cava, Phys. Rev. B 78, 024521 (2008).

Doping Evolution of Antiferromagnetic Order and Structural Distortion in LaFeAsO_1-xF_x, Q. Huang, J. Zhao, J. W. Lynn, G. F. Chen, J. L. Lou, N. L. Wang, and P. Dai, Phys. Rev. B 78, 054529 (2008).

Structural and Magnetic Phase Diagram of CeFeAsO_1-xF_x and its Relationship to High-Temperature Superconductivity, J. Zhao, Q. Huang, C. de al Cruz, S. Li, J. W. Lynn, Y. Chen, M. A. Green, G. F. Chen, G. Li, Z. C. Li, J. L. Luo, N. L. Wang, and P. Dai, Nature Materials 7, 953 (2008).

Spin and Lattice Structure of Single Crystal SrFe₂As_2, Jun Zhao, W. Ratcliff-II, J. W. Lynn, G. F. Chen, J. L. Luo, N. L. Wang, Jiangping Hu, and Pengcheng Dai, Phys. Rev. B 78, 140504(R) (2008).

Low energy spin waves and magnetic interactions in SrFe₂As₂, J. Zhao, D.-X. Yao, S. Li, T. Hong, Y. Chen, S. Chang, W. Ratcliff II, J. W. Lynn, H. A. Mook, G. F. Chen, J. L. Luo, N. L. Wang, E. W. Carlson, J. Hu, and P. Dai, Phys. Rev. Lett. 101, 167203 (2008).

Lattice and Magnetic structures of PrFeAsO, PrFeAsO_0.85F_0.15 and PrFeAsO_0.85, Jun Zhao, Q. Huang, Clarina de la Cruz, J. W. Lynn, M. D. Lumsden, Z. A. Ren, Jie Yang, Xiaolin Shen, Xiaoli Dong, Zhongxian Zhao, and Pengcheng Dai, Phys. Rev. B 78, 132504 (2008).

Pressure-induced Volume-collapsed Tetragonal Phase of CaFe₂As₂ as seen via Neutron Scattering, A. Kreyssig, M. A. Green, Y. B. Lee, G. D. Samolyuk, P. Zajdel, J. W. Lynn, S. L. Bud'ko, M. S. Torikachvili, N. Ni, S. Nandi, J. Leao, S. J. Poulton, D. N. Argyriou, B. N. Harmon, P. C. Canfield, R. J. McQueeney, and A. I. Goldman, Phys. Rev. B 78, 184517 (2008).

The crystalline electric field as a probe for long range antiferromagnetic order and superconductivity in CeFeAsO_1−xF_x, S. Chi, D. T. Adroja, T. Guidi, R. Bewley, Shliang Li, Jun Zhao, J. W. Lynn, C. M. Brown, Y. Qiu, G. F. Chen, J. L. Lou, N. L. Wang, and Pengcheng Dai, Phys. Rev. Lett. 101, 217002 (2008).

Neutron Studies of the Iron-based Family of High Tc Magnetic Superconductors, J. W. Lynn, Mater. Res. Soc. Symp. Proc. 1148E (2008).

Magnetic order in BaFe₂As₂, the parent compound of the FeAs based superconductors in a new structural family, Q. Huang, Y. Qiu, W. Bao, J.W. Lynn, M.A. Green, Y.C. Gasparovic, T. Wu, G. Wu, and X. H. Chen, Phys. Rev. Lett. 101, 257003 (2008).

Crystal Structure and Antiferromagnetic Order in NdFeAsO_1-xF_x (x=0.0 and 0.2) Superconducting Compounds from Neutron Diffraction Measurements, Y. Qiu, W. Bao, Q. Huang, T. Yildirim, J. M. Simmons, M. A. Green, J.W. Lynn, Y.C. Gasparovic, J. Li, T. Wu, G. Wu, and X.H. Chen, Phys. Rev. Lett. 101, 257002 (2008).

Neutron Studies of the Iron-based Family of High T_C Magnetic Superconductors, Jeffrey W. Lynn and Pengcheng Dai, Physica C 469. 469 (2009).