Negative magnetization, complex magnetic ordering and applications of Cr-doped Co2TiO4

Li-ion intercalation-driven control of two-dimensional magnetism in van der Waals FePS3 bilayers

Manipulating two-dimensional (2D) magnetism in layered van der Waals (vdW) materials like FePS3 (FPS), with its wide-ranging applications in flexible spintronic devices, poses a persistent challenge. Through first-principles calculations, we have achieved reversible ferrimagnetic (FiM, FePS3 bilayer) ↔ antiferromagnetic (AFM, 1Li-intercalated FePS3 bilayer) ↔ ferromagnetic (FM, 2Li-intercalated FePS3 bilayer) phase transitions by using a Li-ion intercalation method. Intercalated Li ions significantly enhance the Fe-3d and S-3p hybridization and reduce the Fe-Fe, Li-Fe, Li-S, and Li-P bond lengths. The manipulation of 2D magnetism in Li-intercalated FPS bilayers can be attributed to the charge transfer between two FPS monolayers mediated by Li ions. Moreover, this study offers insights into the underlying physical mechanisms that govern the variations of electronic structures, 2D magnetism, magnetic anisotropy energy, and exchange couplings. Our reversible Li-ion intercalation permits straightforward de-intercalation using a two-step route, thereby reinstating the initial magnetic order of the FPS bilayer. Our purpose-designed FPS bilayer with different Li concentrations and robust exchange coupling not only enriches the Li-intercalation physics in the FPS system but also offers a general pathway for manipulating 2D magnetism in Fe-based vdW trisulfides.

Unconventional Spin State Driven Spontaneous Magnetization in a Praseodymium Iron Antimonide

Consolidating a microscopic understanding of magnetic properties is crucial for a rational design of magnetic materials with tailored characteristics. The interplay of 3d and 4f magnetism in rare-earth transition metal antimonides is an ideal platform to search for such complex behavior. Here the synthesis, crystal growth, structure, and complex magnetic properties are reported of the new compound Pr₃ Fe₃ Sb₇ as studied by magnetization and electrical transport measurements in static and pulsed magnetic fields up to 56 T, powder neutron diffraction, and Mößbauer spectroscopy. On cooling without external magnetic field, Pr₃ Fe₃ Sb₇ shows spontaneous magnetization, indicating a symmetry breaking without a compensating domain structure. The Fe substructure exhibits noncollinear ferromagnetic order below the Curie temperature T_C  ≈ 380 K. Two spin orientations exist, which approximately align along the Fe-Fe bond directions, one parallel to the ab plane and a second one with the moments canting away from the c axis. The Pr substructure orders below 40 K, leading to a spin-reorientation transition (SRT) of the iron substructure. In low fields, the Fe and Pr magnetic moments order antiparallel to each other, which gives rise to a magnetization antiparallel to the external field. At 1.4 K, the magnetization approaches saturation above 40 T. The compound exhibits metallic resistivity along the c axis, with a small anomaly at the SRT.

Effect of Al substitution on the magnetization reversal and complex magnetic properties of NiCr2O4 ceramics

A series of polycrystalline NiCr_2-xAl_xO₄ (0.1 ≤ x ≤ 0.25) spinel ceramics have been synthesized using a sol-gel method. DC magnetization measurements are carried out at different temperatures and magnetic fields. A novel magnetization reversal has been observed in the field cooling process for the x = 0.2 sample, which can be ascribed to the competition between two magnetic sublattices due to their different temperature dependences. The magnetic interaction evolution, related to the complex magnetic properties, is revealed by exchange constants that have been estimated according to ferrimagnetic Curie-Weiss fitting and mean field theory. The fitting result confirmed the evolution of antiferromagnetic and ferromagnetic components with Al substitution, which is supported by the observations from the isothermal magnetization measurements. The positive and negative values of the magnetic moment can be utilized for storage applications based on the results of magnetic switching effect measurements.

Antiferromagnetism, spin-glass state, H-T phase diagram, and inverse magnetocaloric effect in Co2RuO4

Static and dynamic magnetic properties of normal spinel Co2RuO4= (Co2+)A[Co3+Ru3+]BO4are reported based on our investigations of the temperature (T), magnetic field (H) and frequency (f) dependence of the ac-magnetic susceptibilities and dc-magnetization (M) covering the temperature rangeT= 2 K-400 K and H up to 90 kOe. These investigations show that Co2RuO4exhibits an antiferromagnetic (AFM) transition atTN∼ 15.2 K, along with a spin-glass state at slightly lower temperature (TSG) near 14.2 K. It is argued thatTNis mainly governed by the ordering of the spins of Co2+ions occupying theA-site, whereas the exchange interaction between the Co2+ions on theA-site and randomly distributed Ru3+on theB-site triggers the spin-glass phase, Co3+ions on theB-site being in the low-spin non-magnetic state. Analysis of measurements ofM(H,T) forTTN, analysis of the paramagnetic susceptibility (χ) vs.Tdata are fit to the modified Curie-Weiss law,χ=χ0+C/(T+θ), withχ0= 0.0015 emu mol-1Oe-1yieldingθ= 53 K andC= 2.16 emu-K mol-1Oe-1, the later yielding an effective magnetic momentμeff= 4.16μBcomparable to the expected value ofμeff= 4.24μBper Co2RuO4. UsingTN,θand high temperature series forχ, dominant exchange constantJ1/kB∼ 6 K between the Co2+on theA-sites is estimated. Analysis of the ac magnetic susceptibilities nearTSGyields the dynamical critical exponentzν= 5.2 and microscopic spin relaxation timeτ0∼ 1.16 × 10-10sec characteristic of cluster spin-glasses and the observed time-dependence ofM(t) is supportive of the spin-glass state. LargeM-Hloop asymmetry at low temperatures with giant exchange bias effect (HEB∼ 1.8 kOe) and coercivity (HC∼ 7 kOe) for a field cooled sample further support the mixed magnetic phase nature of this interesting spinel. The negative magnetocaloric effect observed belowTNis interpreted to be due to the AFM and SG ordering. It is argued that the observed change from positive MCE (magnetocaloric effect) forT>TNto inverse MCE forT Collapse

Key Words

• antiferromagnetism
• exchange bias
• spin-glass state

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Affiliation(s)

Sayandeep Ghosh Department of Physics, Indian Institute of Technology, Guwahati-781039, Assam, India
Deep Chandra Joshi Department of Materials Science and Engineering, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
Prativa Pramanik Department of Physics, Indian Institute of Technology, Guwahati-781039, Assam, India
Suchit K Jena Department of Physics, Indian Institute of Technology, Guwahati-781039, Assam, India
Suresh Pittala Department of Physics, Indian Institute of Science, Bangalore-560012, Karnataka, India
Tapati Sarkar Department of Materials Science and Engineering, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden
Mohindar S Seehra Department of Physics & Astronomy, West Virginia University, Morgantown, WV 26506, United States of America
Subhash Thota Department of Physics, Indian Institute of Technology, Guwahati-781039, Assam, India

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