Large magnetic anisotropy in highlyc-axis-orientedRuEu1.5Ce0.5Sr2Cu2

Abstract

We investigated the magnetic properties in Ru͑Eu 1.5 Ce 0.5 ͒Sr 2 Cu 2 O 10−␦ ͑Ru-1222͒ epitaxial films. Large magnetic anisotropy was observed, showing that the c axis is the hard axis of magnetization, while all the directions in the ab plane are isotropic easy axes for magnetization. A possible arrangement of the Ru moments is suggested to interpret the magnetic anisotropy as well as the complex magnetic properties of Ru-1222 including the ferromagnetic, the antiferromagnetic, and the spin-glass behaviors.

The magnetic state of 1212-type ruthenocuprate in magnetocaloric and magnetoresistivity measurements of polycrystalline samples of RuSr2Gd1−xCexCu2O8and Ru1−xSr2GdCu2O8

“…The model was essentially meant for reflecting on the experimentally suggested frustrated magnetic ground state and for the presence of the magnetic-field induced ferromagnetism in the a-b plane of the investigated films. Since our measurements of the isothermal magnetocaloric coefficient indicate the absence of the spontaneous ferromagnetism, this would match the conclusion formed in [38] with the additional requirement that the antiferromagnetic order would not dominate the system's net magnetic entropy. The positive magnetoresistivity (see figures 6 and 10) is limited to low temperatures and weak magnetic fields, which also suggests the otherwise dominant role of ferromagnetic correlations affecting the electron scattering.…”

“…Most of the models of the magnetic ordering in the Ru sublattice were formulated for the experimental data collected for the polycrystalline samples, for which it is difficult to account for expected anisotropy of the magnetic system. It is then worth mentioning the recent analysis of the magnetization data for epitaxial thin films of RuSr 2 GdCu 2 O 8 , in which the ferromagnetic component of ordering was considered to form cluster type domains out of planar components of the Ru moments, proposed there to couple within a-b planes with weak and long range dipolar interactions [38]. The model was essentially meant for reflecting on the experimentally suggested frustrated magnetic ground state and for the presence of the magnetic-field induced ferromagnetism in the a-b plane of the investigated films.…”

“…For the field-dependent anisotropy of this magnetic system, we might be accessing a similar effect by the field-induced changes in the direction of the magnetic induction vector, which acts on the superconducting layers in the crystallites [41]. formed in [38] with the additional requirement that the antiferromagnetic order would not dominate the system's net magnetic entropy. The positive magnetoresistivity (see figures 6 and 10) is limited to low temperatures and weak magnetic fields, which also suggests the otherwise dominant role of ferromagnetic correlations affecting the electron scattering.…”

The Superconducting and Magnetic States in RuSr2GdCu2O8, Based on the Magnetic, Transport and Magneto-Caloric Characteristics

“…It may be noted that since the effect of magnetic field is to increase the T m , it would be less usual to assume the antiferromagnetic type of interactions as leading to 3D long range order at T m . Note that a considerable shift of T m occurs at comparatively small field values -which may suggest substantial magnetic anisotropy of the probed system, in agreement with same assumed for modelling the ground state with AFM-I magnetic structure [13] or in the hyphotesis of progressing the 3D ordering with long range, weak dipolar interactions (formulated in [33] for the related 1222-type structure ruthenate-cuprate). The different slope of the T m (H) dependencies estimated in Fig.…”

“…Note that a considerable shift of T m is observed for comparatively weak fields -in consideration of the role of magnetic anisotropy, for already proposed models involving the field induced rotation of planar easy magnetisation axes [12] or progressing the spatial ordering with long range but weak planar dipolar interactions (formulated in [33] for the related structure of 1222-type ruthenatecuprate), remains intuitive for such data. Then, primary role of the magnetic field in temperature vicinity of the transition would be in locking in the 3D long range spatial order.…”