Magnetic structure of the magnetoelectric material Ba 2 MnGe 2 O 7

Physical review. B./Physical review. B, vol. 108

Abstract

A detailed investigation of ${\mathrm{Ba}}_{2}{\mathrm{MnGe}}_{2}{\mathrm{O}}_{7}$ was performed in its low-temperature magnetoelectric state combining neutron diffraction with magnetization measurements on single crystals. In the paramagnetic state at 10 K, polarized neutron diffraction was applied to reveal the components of the susceptibility tensor. The crystal and magnetic structures below the antiferromagnetic transition temperature of ${T}_{\text{N}}\ensuremath{\approx}4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ were determined using unpolarized neutron diffraction. These data imply no structural phase transition from 10 K down to 2.5 K and are well described within the tetragonal space group $P\overline{4}{2}_{1}m$. We found that in zero magnetic field the magnetic space group is either ${C}_{c}mc{2}_{1}$ or ${P}_{c}{2}_{1}{2}_{1}{2}_{1}$ with antiferromagnetic order along the [110] or [100] direction, respectively, while neighboring spins along the [001] axis are ordered antiferromagnetically. A noncollinear spin arrangement due to small canting within the $ab$ plane is allowed by symmetry and observed experimentally. The ordered moment is found to be 3.24(3) ${\ensuremath{\mu}}_{\text{B}}/{\mathrm{Mn}}^{2+}$ at 2.5 K and the temperature-field dependent magnetic phase diagram is mapped out by macroscopic magnetization. Distinct differences between the magnetic structure of ${\mathrm{Ba}}_{2}{\mathrm{MnGe}}_{2}{\mathrm{O}}_{7}$ as compared to those of ${\mathrm{Ba}}_{2}{\mathrm{CoGe}}_{2}{\mathrm{O}}_{7}$ and ${\mathrm{Ca}}_{2}{\mathrm{CoSi}}_{2}{\mathrm{O}}_{7}$ are discussed.

Authors 10

1. Andrew Sazonov

   European Spallation Source

   Affiliation as printed

   European Spallation Source ERIC, P.O. Box 176, SE-221 00 Lund, Sweden

2. Henrik Thoma Aachen Institute of Crystallography

   RWTH Aachen University · Heinz Maier-Leibnitz Zentrum

   Affiliation as printed

   Institute of Crystallography, RWTH Aachen University and Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), 85748 Garching, Germany

3. Rajesh Dutta Aachen Institute of Crystallography

   RWTH Aachen University · Heinz Maier-Leibnitz Zentrum

   Affiliation as printed

   Institute of Crystallography, RWTH Aachen University and Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), 85748 Garching, Germany

4. Martin Meven Aachen Institute of Crystallography

   RWTH Aachen University · Heinz Maier-Leibnitz Zentrum

   Affiliation as printed

   Institute of Crystallography, RWTH Aachen University and Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), 85748 Garching, Germany

5. Arsen Gukasov

   Centre National de la Recherche Scientifique · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · CEA Paris-Saclay · Laboratoire Léon Brillouin

   Affiliation as printed

   Laboratoire Léon Brillouin, CEA-CNRS, CE-Saclay, 91191 Gif-sur-Yvette, France

6. R. Fittipaldi

   University of Salerno

   Affiliation as printed

   CNR-SPIN c/o University of Salerno, 84084 Fisciano, Italy

7. V. Granata

   University of Salerno

   Affiliation as printed

   Department of Physics “E.R. Caianiello”, University of Salerno, 84084 Fisciano, Italy

   Department of Physics "E.R. Caianiello", University of Salerno, 84084 Fisciano, Italy

8. Takatsugu Masuda

   The University of Tokyo

   Affiliation as printed

   Institute for Solid State Physics, The University of Tokyo, Chiba 277-8581, Japan

9. Bálint Náfrádi

   École Polytechnique Fédérale de Lausanne

   Affiliation as printed

   École Polytechnique Fédérale de Lausanne, Laboratory of Nanostructures and Novel Electronic Materials, 1015 Lausanne, Switzerland

10. Vladimir M. Hutanu Aachen Institute of Crystallography

    RWTH Aachen University · Heinz Maier-Leibnitz Zentrum

    Affiliation as printed

    Institute of Crystallography, RWTH Aachen University and Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), 85748 Garching, Germany