Eur. Phys. J. B (2013) 86: 280
https://doi.org/10.1140/epjb/e2013-40019-2

Regular Article

Magnetic phase diagram and correlation between metamagnetism and superconductivity in Ru_0.9Sr₂YCu_2.1O_7.9

¹ Institute for Superconducting and Electronic Materials, University of Wollongong, Northfields Avenue, Wollongong, NSW 2522, Australia
² Bragg Institute, Australian Nuclear Science and Technology Organization, New Illawarra Road, Lucas Heights, NSW 2234, Australia

^a e-mail: pan@uow.edu.au

Received: 9 January 2013
Received in final form: 19 April 2013
Published online: 19 June 2013

Abstract

The magnetic superconductor Ru_0.9Sr₂YCu_2.1O_7.9 (Ru-1212Y) has been investigated using neutron diffraction under variable temperature and magnetic field. With the complementary information from magnetization measurements, we propose a magnetic phase diagram T-H for the Ru-1212 system. Uniaxial antiferromagnetic (AFM) order of 1.2μ_B/Ru atoms with moments parallel to the c-axis is found below the magnetic transition temperature at  ~140 K in the absence of magnetic field. In addition, ferromagnetism (FM) in the ab-plane develops below  ~120 K, but is suppressed at lower temperature by superconducting correlations. Externally applied magnetic fields cause Ru-moments to realign from the c-axis to the ab-plane, i.e. along the ⟨1,1,0⟩ direction, and induce ferromagnetism in the plane with  ~1μ_B at 60 kOe. These observations of the weak ferromagnetism suppressed by superconductivity and the field-induced metamagnetic transition between AFM and FM demonstrate not only competing orders of superconductivity and magnetism, but also suggest a certain vortex dynamics contributing to these magnetic transitions.