We have prepared perpendicular hard/soft bilayers made of a 10nm L10-FePt layer, which has been epitaxially grown on MgO(100) and a Fe layer with thicknesses of 2 and 3.5nm. The control of the interface morphology allows to modify the magnetic regime at fixed Fe thickness (from rigid magnet to exchange-spring magnet), due to the nanoscale structure effect on the hard/soft coupling and to tailor the hysteresis loop characteristics. Despite the small thickness of the soft layer, the coercivity is strongly reduced compared to the hard layer value, indicating that high anisotropy perpendicular systems with moderate coercivity can be easily obtained.

We studied the structural and physical properties of powder samples of the high-pressure ${\text{LaMn}}_7{\text{O}}_{12}$ compound by means of neutron diffraction, dc magnetization, specific-heat, and dc electrical resistivity measurements. Our structural refinement shows that ${\text{LaMn}}_7{\text{O}}_{12}$ is the counterpart with quadruple perovskite structure of the well-known simple-perovskite ${\text{LaMnO}}_3$ because both compounds are single-valent ${\text{Mn}}^{3+}$ systems sharing a similar pseudocubic network of buckled corner-sharing ${\text{MnO}}_6$ octahedra distorted by the Jahn-Teller (JT) effect. Besides this similarity, ${\text{LaMn}}_7{\text{O}}_{12}$ exhibits the following structural differences: (i) a monoclinic $I2/m$, instead of orthorhombic $Pnma$, structure; (ii) a much larger buckling of the ${\text{MnO}}_6$ octahedra, corresponding to a Mn-O-Mn bond angle as small as $\psi =180°-\varphi =136°$. At $T_{N,B}=78\text{K}$, the neutron data show evidence of an antiferromagnetic (AFM) structure of the octahedral ${\text{Mn}}^{3+}$ ions ($B$ sites), which consists of ferromagnetically coupled antiferromagnetic $ac$ planes. This structure, commonly referred to as $C$ type, markedly differs from the $A$-type structure of ${\text{LaMnO}}_3$, which consists of antiferromagnetically coupled ferromagnetic $ac$ planes. We argue that this difference may be due not only to the different buckling, because the magnetic superexchange interaction is sensitive to $\varphi$, but also to the existence of two distinct JT distorted $B$ sites, a characteristic feature of the quadruple perovskite structure not found in ${\text{LaMnO}}_3$. A further feature of this structure is the presence of a pseudocubic sublattice of JT ${\text{Mn}}^{3+}$ ions with square coordination ($A^{\prime }$ site) in addition to the $B$-site sublattice. At $T_{N,A^{\prime }}=21\text{K}$, the $A^{\prime }$ sublattice of ${\text{LaMn}}_7{\text{O}}_{12}$ is found to form a second AFM structure consisting of AFM coupled ferromagnetic planes. This additional ordering appears to occur independently of that of the $B$ sublattice. Finally, we observed a thermally activated insulating behavior of the resistivity similar to that previously reported for ${\text{LaMnO}}_3$, which confirms the hypothesis that the superexchange interaction is predominant in single-valent systems while the double-exchange interaction is relevant only in mixed-valence or disordered systems.

We report on the high-pressure synthesis of ${\text{BiMn}}_7{\text{O}}_{12}$, a manganite displaying a “quadruple-perovskite” structure. Structural characterization of single-crystal samples shows a distorted and asymmetrical coordination around the Bi atom due to presence of the $6{\text{s}}^2$ lone pair, resulting in noncentrosymmetric space group $Im$, leading to a permanent electrical dipole moment and ferroelectric properties. On the other hand, magnetic characterization reveals antiferromagnetic transitions in agreement with the isostructural compounds, and the dielectric constant shows anomalies matching the magnetic transition temperatures. ${\text{BiMn}}_7{\text{O}}_{12}$ is therefore a promising multiferroic material, with evidence of coupling between magnetic and dielectric properties.

We studied the composition dependence of the structural and magnetic properties of Co-doped Ni–Mn–Ga alloys around the Mn-rich composition ${\text{Ni}}_{50}{\text{Mn}}_{30}{\text{Ga}}_{20}$ . By varying the Co and Mn content we have been able to tune the critical temperatures. In particular, in a suitable composition range, the Curie temperature of martensite is lower than Curie temperature of austenite and lower than martensitic transformation temperature, giving rise to a paramagnetic gap between magnetically ordered martensite and austenite and to the occurrence of a reverse magnetostructural transformation.