Correlations between magnetic transition temperatures and the average weighted valence band electron concentration ((s + d) electrons/atom) have led to the development of a phenomenological model that predicts the influence of elemental substitution on the magnetostructural response of bulk B2-ordered Fe(Rh_1−xM_x) or (Fe_1−xM_x)Rh alloys (M = transition elements; x < 6 at. %). Validation of this model is provided through synthesis and characterization of FeRh with Cu and Au additions. The data and associated trends indicate that the lattice and electronic free energies are both equally important in driving the magnetostructural transition in the bulk FeRh system.

Experimental evidence for magnetothermal behavior in iron-iron oxide nanostructured systems has been obtained using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Fe L2,3 edges. The purpose of this study is the determination of the blocked state in these spin-glass-like core-shell systems. A first overview of the magnetic species participating in the magnetic response was obtained by analyzing the XMCD at saturating fields. Also, the XAS revealed the existence of an antiferromagnetic FeO phase, likely located at the interface regions. Finally, measurements were performed at low temperature and intermediate field, where a frozen state below the blocking energy is observed. The results show that the oxide phase spins are oriented at low temperature, while the magnetic spins of the metallic core do not contribute to the XMCD, suggesting that the blocking process mainly involves the magnetic particle superspins rather than the oxide coverage phase.

In this work, we demonstrate that the magnetocaloric response of FeRh-based compounds may be tailored for potential magnetic refrigeration applications by chemical modification of the FeRh lattice. Alloys of composition Fe(Rh_1−xA_x) or (Fe_1−xB_x)Rh (A = Cu, Pd; B = Ni; 0 < x < 0.06) were synthesized via arc-melting and subsequent annealing in vacuum at 1000 °C for 48 h. The magnetocaloric properties of the FeRh-based systems were determined using isothermal M(H) curves measured in the vicinity of the magnetostructural temperature (T_t). It is found that the FeRh working temperature range (δT_FWHM) may be chemically tuned over a wide temperature range, 100 K ≤ T ≤ 400 K. While elemental substitution consistently decreases the magnetic entropy change (ΔS_mag) of the FeRh-based ternary alloys from that of the parent FeRh compound (ΔS_mag,_FeRh ∼ 17 J/kg K; ΔS_{mag,FeRh-ternary =} 7–14 J/kg K at H_app = 2 T), the net refrigeration capacity (RC), defined as the amount of heat that can be transferred during one magnetic refrigeration cycle, of the modified systems is significantly higher (RC_FeRh ∼ 150 J/kg; RC_{FeRh-ternary =} 170–210 J/kg at H_app = 2 T). These results are attributed to stoichiometry-induced changes in the FeRh electronic band structure and beneficial broadening of the magnetostructural transition due to local chemical disorder.