We report an unusual canted magnetism due to 3d and 4f electrons, occupying two different crystallographic sites, with its consequence to electric dipole order. This is based on neutron powder diffraction measurements on Tb2BaNiO5 (orthorhombic, Immm centrosymmetric space group), exhibiting Néel order below (TN=) 63 K, to understand multiferroic behavior below 25 K. The magnetic structure is made up of Ni and Tb magnetic moments, which are found to be mutually canted in the entire temperature range below TN, though collinearity is seen within each sublattice, as known in the past. First-principles density functional theory calculations (GCA+SO and GGA+U+SO approximations) support such a canted ground state. The intriguing finding, being reported here, is that there is a sudden increase in this Tb-Ni relative canting angle at the temperature (that is, at 25 K) at which spontaneous electric polarization sets in, with bond distance and bond angle anomalies. This finding emphasizes the need for a new spin-driven polarization mechanismthat is, a critical canting angle coupled with exchangestriction -to induce multiferroicity in magnetic insulators with canted spins.

We report temperature (T) dependence (2-300 K) of DC and AC magnetization (M), isothermal remnant magnetization (MIRM), heat-capacity (C), electrical resistivity (ρ), and magnetoresistance (MR) of a ternary intermetallic compound, Gd4PtAl, crystallizing in a cubic (space group F4 3m) structure. In this structure, there are three sites for the rare-earth. The magnetization data reveal that, in addition to a magnetic transition at 64 K, there is another magnetic feature below 20 K. The C(T) data reveal an upturn below 64 K, shifting to a lower temperature with increasing field, which establishes that the onset of magnetic order is of an antiferromagnetic type. However, there is no worthwhile feature near 20 K in the C(T) curve. Ac susceptibility peak undergoes an observable change with frequency and, in particular the peak around 20 K gets suppressed with the application of a dc magnetic field; in addition, MIRM undergoes a slow decay with time and isothermal M exhibits low-field hysteresis below 20 K only, which are typical of spin-glasses. The results overall suggest that this compound is a reentrant spinglass in zero field. There are experimental signatures pointing to the existence of both antiferromagnetic and ferromagnetic components, competing with the variation of temperature and magnetic field, as a result of which electrical and magnetoresistance behaviors are peculiar. The results overall suggest that this compound exhibits interesting magnetic and transport properties.

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