The Structure And Magnetism Of Orthochromites Ho_1-xY_xCrO₃

The rare earth transition metal oxides and the doping system in A/B site,which derived from ABO₃ type perovskite,show rich physical properties due to the spin reorientation behavior and coupling between low spatial symmetry and spin system,such as superconductivity,ferromagnetism,magnetocaloric phenomenon,giant magnetoresistance effect and so on.These properties have aroused the research interesting of researchers.In rare earth chromium oxide,the different rare earth elements in A site can generate huge impact on the magnetic structure and performance.Therefore,study coupling effect between the rare earth ions and the transition metal on magnetic structure and properties have great significance.In this paper,the Y³⁺ions are doped into HoCrO₃ matrix at Ho³⁺site to investigate structure and magnetic properties.The doping of Y³⁺ions cannot reduce huge lattice distortion but change the Ho³⁺ion content,because the non-magnetic Y³⁺ions and magnetic Ho³⁺ions have almost the same ionic radius.The crystal structure,kinetics,magnetic structure and properties of Ho_1-xY_xCrO₃ were studied via X-ray diffraction,Raman spectroscopy,magnetic characterization and neutron powder diffraction.The research results are listed as follow:1.With increasing content of Y³⁺,the structural parameters and the Néel temperature?T_N?associated with the crystal structure have no significant change,because of the same ionic radius between Ho³⁺and Y³⁺ions.However,the effective magnetic moment gradually decreases,because the total magnetic moment caused by content of magnetic Ho³⁺ions are effectively modulated by non-magnetic Y³⁺ions.2.The Raman spectroscopy indicates that the Y³⁺ions doping lead to a distinct relevant Raman shifts and new phonon modes appear in lower wavenumber phonon modes(100–220 cm^-1).The appearance of the new phonon modes are associated with the motion of A-site atoms in ACrO₃,hence the intrinsic reason is that large difference of atomic masses between Ho³⁺and Y³⁺ions not only breaking the symmetry,but also disturbing the kinetics of the crystal.The high wavenumber phonon modes originated from the vibration of Cr³⁺and O^2-ions have no obvious change indicating the stability of CrO₆ octahedrons.3.The Cr³⁺sub-lattice adopts canted antiferromagnetic at the order temperature141 K.The interesting spin reorientation is founded below the ordered temperature.This can be attributed to the weakened Ho–Cr interaction with the increasing content of Y³⁺ions.?1?For the composition of x?0.6,the Cr³⁺sublattice adopts?38?₂?F_x,C_y,G_z?magnetic configuration begin at low temperature to Néel temperature,which is due to the stronger superexchange interaction of Ho³⁺-Cr³⁺.?2?For the composition of x=0.7,a single spin structure is identified as?38?₂emerged in the temperature range 10-60 K.But the system exhibits a mixed-domain structure of??38?₂+?38?₄?at the temperature range 60-140 K.?3?For x=0.8,the system exhibits a mixed-domain structure of??38?₂+?38?₄?at the temperature range 30-100 K.A single spin structure is identified as?38?₄?G_x,A_y,F_z?and?38?₂ beyond and underneath this temperature range,respectively.With the further increase of doping concentration,the superexchange interaction of Cr³⁺-Cr³⁺play a dominant role in this system and the magnetic structure caused by Ho³⁺-Cr³⁺interaction is diminished.We summarized the results of this research in a phase diagram.We design Ho_1-xY_xCrO₃,which keep the crystal structure and effectively control the content of magnetic Ho³⁺ions.Then,further explore the effect of superexchange between the rare earths metal and transition metals atoms on the magnetic structure and the spin orientation behavior.The rich magnetic structure and spin reorientation behavior were not only induced by the temperature,but also affected by the Ho³⁺-Cr³⁺superexchange interaction and Cr³⁺-Cr³⁺superexchange interaction.The results provide experimental support for the further design of rare earth transition metal oxide magnetic materials.It is of great significance for further exploring new multifunctional magnetic materials.