Abstract
The magnetic domain evolution behavior under external field stimuli of temperature and magnetic field in PrMn2Ge0.4Si1.6 compound is investigated using Lorentz transmission electron microscopy. A spontaneous 180° magnetic domain is observed at room temperature and it changes with temperature. Dynamic magnetization process is related to the rotation of magnetic moments, resulting in the transforming of magnetic domains from 180° type to a uniform ferromagnetic state with almost no pinning effects under the in-plane magnetic field at room temperature. X-ray powder diffraction is performed on PrMn2Ge0.4Si1.6 at different temperatures to study the temperature dependence of crystal structure and lattice parameter.
Highlights
INTRODUCTIONThe studies of RMn2X2 (R is a rare earth and X is Si or Ge) compounds have attracted a great deal of attentions due to their layered crystal structure and interesting physical phenomena, such as coupled magnetic and crystallographic transitions or valence-related transitions, superconductivity, heavy fermion and Kondo behaviour.[1,2,3,4,5,6,7] The RMn2X2 alloys have a body centered tetragonal ThCr2Si2-type structure with space group I4/mmm and exhibit a vast variety of magnetic structures and magnetic phase transitions with temperature, mechanical pressure or magnetic field[8,9,10] due to the fact that the magnetic states of Mn-sublattice are sensitive to the inter-planar and intra-planar Mn–Mn distances.[11,12,13,14] Four magnetic transitions are observed in pure PrMn2Ge2 phase below 500 K15,16 while one relatively simple antiferromagnetic transition exist below 368 K in PrMn2Si2.17 The substitution of Si for Ge leads to a linear decrease of the lattice constants and the magnetic state changes from the ferromagnetic ordering of PrMn2Ge2 to the antiferromagnetic ordering of PrMn2Si2 at room temperature due to the atomic size difference between Si and Ge.[16]
Antiferromagnetism exits in the samples with x >1.6 and the re-entrant ferromagnetism with co-existence of canted ferromagnetism and antiferromagnetism is observed in the cases of x = 1.2 or 1.3 below the magnetic transition temperature.[16,18]
The evolution of the magnetic domains and the crystal structures induced by temperature are investigated in PrMn2Ge0.4Si1.6 alloy by means of in situ Lorentz transmission electron microscopy (LTEM) and X-ray diffraction, respectively
Summary
The studies of RMn2X2 (R is a rare earth and X is Si or Ge) compounds have attracted a great deal of attentions due to their layered crystal structure and interesting physical phenomena, such as coupled magnetic and crystallographic transitions or valence-related transitions, superconductivity, heavy fermion and Kondo behaviour.[1,2,3,4,5,6,7] The RMn2X2 alloys have a body centered tetragonal ThCr2Si2-type structure with space group I4/mmm and exhibit a vast variety of magnetic structures and magnetic phase transitions with temperature, mechanical pressure or magnetic field[8,9,10] due to the fact that the magnetic states of Mn-sublattice are sensitive to the inter-planar and intra-planar Mn–Mn distances.[11,12,13,14] Four magnetic transitions are observed in pure PrMn2Ge2 phase below 500 K15,16 while one relatively simple antiferromagnetic transition exist below 368 K in PrMn2Si2.17 The substitution of Si for Ge leads to a linear decrease of the lattice constants and the magnetic state changes from the ferromagnetic ordering of PrMn2Ge2 to the antiferromagnetic ordering of PrMn2Si2 at room temperature due to the atomic size difference between Si and Ge.[16]. Two magnetic phase transitions above room temperature and a canted antiferromagnetic structure at room temperature are expected in PrMn2Ge0.4Si1.6 based on previous report.[18] the magnetic transition is evident in magnetic measurements at ∼282 K, no ferromagnetic component is detected below 282 K from the neutron diffraction patterns,[18] similar to PrMn1.2Fe0.8Ge2.20,21 studying the magnetic domain structures during in-situ magnetization and phase transformation will provide a fruitful playground for the exploration of fundamental physics of this anomaly phenomenon. The evolution of the magnetic domains and the crystal structures induced by temperature are investigated in PrMn2Ge0.4Si1.6 alloy by means of in situ Lorentz transmission electron microscopy (LTEM) and X-ray diffraction, respectively. The dynamic behavior of the magnetic domain walls under the in-plane magnetic field is demonstrated at room temperature using LTEM providing enhanced understanding of magnetic phases in PrMn2Ge0.4Si1.6 alloy
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