A Magnetic Transition Probed by the Ce Ion in Square-Lattice Antiferromagnet CeMnAsO (original) (raw)
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Spin reorientation and Ce-Mn coupling in antiferromagnetic oxypnictide CeMnAsO
Physical Review B, 2015
Structure and magnetic properties of high-quality polycrystlline CeMnAsO, a parent compound of the "1111"-type oxypnictides, have been investigated using neutron powder diffraction and magnetization measurements. We find that CeMnAsO undergoes a C-type antiferromagnetic order with Mn 2+ (S = 5/2) moments pointing along the c-axis below a relatively high Néel temperature of TN = 345 K. Below TSR = 35 K, two instantaneous transitions occur where the Mn moments reorient from the c-axis to the ab-plane preserving the C-type magnetic order, and Ce moments undergo long-range AFM ordering with antiparallel moments pointing in the ab-plane. Another transition to a noncollinear magnetic structure occurs below 7 K. The ordered moments of Mn and Ce at 2 K are 3.32(4) µB and 0.81(4)µB, respectively. We find that CeMnAsO primarily falls into the category of a local-moment antiferromagnetic insulator in which the nearest-neighbor interaction (J1) is dominant with J2 < J1/2 in the context of J1 − J2 − Jc model. The spin reorientation transition driven by the coupling between rare earth Ce and transition metal seems to be common to Mn, Fe and Cr ions, but not to Co and Ni ions in the iso-structural oxypnictides. A schematic illustration of magnetic structures in Mn and Ce sublattices in CeMnAsO is proposed.
Magnetic field induced phase transition in Ce 2 Fe 17-x Mn x compounds
Applied Physics A: Materials Science & Processing, 2002
The atomic and magnetic structures of Ce 2 Fe 17−x Mn x compounds with x = 0.5 and 1.0 were investigated using neutron diffraction under magnetic fields up to 5.0 T over the temperature range 2 − 300 K. The magnetic reflexes observed at temperatures 2 − 208 K and µ 0 H = 0 T correspond to an incommensurate antiferromagnetic structure with wave vector [0, 0, 0 ± τ] at 2 K. This structure is suppressed in an external magnetic field and a ferromagnetic phase is induced in fields higher than 0.6 T. The complex transformation of the magnetic structures under magnetic field and temperature is analyzed and discussed.
Comparative study of the ferro-antiferromagnetic transition in Ce(Fe,Co)2 and Ce(Fe,Al)2
Journal of Alloys and Compounds, 1997
The magnetic, thermal and transport properties of Ce(Fe,Co), and Ce(Fe,AI) 2 around the ferro-antiferromagnetic (F-AF) transition are studied and compared in their thermodynamic aspects. We confirm the presence of a structural contribution to the enthalpy of the transition in the case of Co substituuon, which is the main difference between the AF phase transitions in both systems. The role of the Ce hybridization in the Co case and the "canted" nature of the AF phase in Ce(Fe,Ai) 2 are discu~'~sed.
Rare earth magnetism in CeFeAsO: a single crystal study
Single crystals of CeFeAsO, large enough to study the anisotropy of the magnetic properties, were grown by an optimized Sn-flux technique. The high quality of our single crystals is apparent from the highest residual resistivity ratio (RRR) ≈ 12, reported among undoped RFeAsO compounds (R = rare earth) as well as sharp anomalies in resistivity, specific heat, C(T ), and thermal expansion at the different phase transitions. The magnetic susceptibility χ(T ) presents a large easy-plane anisotropy consistent with the lowest crystal electric field doublet having a dominant 6 character. Curie-Weiss-like susceptibilities for magnetic field parallel and perpendicular to the crystallographic c-axis do not reveal an influence of a staggered field on the Ce site induced by magnetic ordering of the Fe. Furthermore, the standard signatures for antiferromagnetic order of Ce at T 4f N = 3.7 K observed in χ(T ) and C(T ) are incompatible with a Zeeman splitting ≈ 10 K of the CEF ground state doublet at low temperature due to the Fe-magnetic order as previously proposed. Our results can be reconciled with the earlier observation by assuming a comparatively stronger effect of the Ce-Ce exchange leading to a reduction of this Zeeman splitting below 15 K.
The Journal of Physical Chemistry C, 2011
We report the structural and magnetic properties of La 0.2 Ca 0.8 MnO 3 nanoparticles synthesized by a chemical route, having an average diameter of 15 nm. Synchrotron experiments performed in the temperature range 80-300 K have shown that below 200 K a structural transition from room temperature orthorhombic Pnma to monoclinic P2 1 /m space group, associated with orbital ordering, survives in studied particles, although this transition is highly suppressed in comparison with that of the bulk. The magnetization of these particles exhibits the appearance of a ferromagnetic contribution from the shell at T > 200 K, antiferromagnetic ordering within the particle core at T N ∼ 140 K, and the emergence of another ferromagnetic contribution at T < 100 K. The latter appears as a result of spin canting within the antiferromagnetic core or is developed at some interfaces inside the nanoparticles. Considerable horizontal (H EB ) and vertical (M Shift ) shifts of the magnetization hysteresis loops are observed after field cooling, manifesting the exchange bias (EB) effect. We found that a nonmonotonic variation of H EB and M Shift as well as of the coercive field (H C ) can be caused by the changes in the temperature at which the cooling field (H cool ) is applied. The maximum values of negative H EB and positive M Shift are obtained when H cool = 15 kOe is applied between 100 and 200 K. Moreover, the exchange bias field, the remanent magnetization, the coercive field, as well as the magnitude of the vertical shift depend strongly on the magnitude of H cool . Our studies show that the volume fraction of the ferromagnetic phase, the strength of the interfacial exchange, and the topology of phase separation are altered clearly by the procedure of application of the magnetic field. The existence of two interfaces contributing to the total EB effect is proposed to explain the observed effects.