Metamagnetism

About: Metamagnetism is a research topic. Over the lifetime, 2023 publications have been published within this topic receiving 38108 citations.

Effects of external pressure on the 5f-band metamagnetism in UCoAl

Abstract: UCoAl exhibits below 16 K anisotropic 5f-band metamagnetism induced by magnetic fields as low as \ensuremath{\sim}1 T applied along the c axis of the hexagonal structure. No metamagnetic transition is observed in fields up to 40 T applied within the basal plane. The critical field of the metamagnetic transition ${\mathrm{B}}_{\mathrm{c}}$ is composition dependent within the homogeneity range. The metamagnetic transition is found to be very sensitive to external pressure. The value of ${\mathrm{B}}_{\mathrm{c}}$ increases with the rate ${\mathrm{dB}}_{\mathrm{c}}$ /dp=0.27 T/kbar, whereas the magnetization gained through the transition becomes reduced. The critical pressure of 24 kbar (corresponding to \ensuremath{\sim}2% volume contraction) for disappearance of metamagnetism in UCoAl has been estimated. Relations of UCoAl to 3d-band metamagnets are discussed.

Experimental Evidence for Anisotropic Interactions in Some Rare‐Earth Intermetallic Compounds

Abstract: We have studied the magnetic properties of the rare‐earth alloys RAl, RNi, and R3Ni, with R = Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm, in high magnetic fields up to 70 kOe. For the three series, the magnetic properties differ according to the alloyed rare earth. The compounds RAl of DyAl type and RNi of FeB type are ferromagnetic or antiferromagnetic. The compounds R3Ni exhibit metamagnetism, except Tm3Ni which has a ferromagnetic behavior. We have studied the magnetic structure of NdAl, TbAl, HoAl, ErAl, TmAl, NdNi, ErNi, HoNi, and Er3Ni by neutron diffraction. They have all a noncolinear magnetic structure except NdNi, in which the magnetic moments are parallel. We have studied the stability of the magnetic structures by means of group theory; they are all stabilized by strongly anisotropic magnetic interactions between rare‐earth atoms.

Magnetic entropy change involving martensitic transition in NiMn-based Heusler alloys

Abstract: Our recent progress on magnetic entropy change (ΔS) involving martensitic transition in both conventional and metamagnetic NiMn-based Heusler alloys is reviewed. For the conventional alloys, where both martensite and austenite exhibit ferromagnetic (FM) behavior but show different magnetic anisotropies, a positive ΔS as large as 4.1 Jkg−1 K−1 under a field change of 0–0.9 T was first observed at martensitic transition temperature TM ~ 197 K. Through adjusting the Ni:Mn:Ga ratio to affect valence electron concentration e/a, TM was successfully tuned to room temperature, and a large negative ΔS was observed in a single crystal. The −ΔS attained 18.0 Jkg−1K−1 under a field change of 0–5 T. We also focused on the metamagnetic alloys that show mechanisms different from the conventional ones. It was found that post-annealing in suitable conditions or introducing interstitial H atoms can shift the TM across a wide temperature range while retaining the strong metamagnetic behavior, and hence, retaining large magnetocaloric effect (MCE) and magnetoresistance (MR). The melt-spun technique can disorder atoms and make the ribbons display a B2 structure, but the metamagnetic behavior, as well as the MCE, becomes weak due to the enhanced saturated magnetization of martensites. We also studied the effect of Fe/Co co-doping in Ni45(Co1−xFex)5Mn36.6In13.4 metamagnetic alloys. Introduction of Fe atoms can assist the conversion of the Mn—Mn coupling from antiferromagnetic to ferromagnetic, thus maintaining the strong metamagnetic behavior and large MCE and MR. Furthermore, a small thermal hysteresis but significant magnetic hysteresis was observed around TM in Ni51Mn49−xInx metamagnetic systems, which must be related to different nucleation mechanisms of structural transition under different external perturbations.

Theory of unconventional metamagnetic electron states in orbital band systems

Abstract: We extend the study of the Fermi surface instability of the Pomeranchuk type into systems with orbital band structures, which are common features in transition metal oxides. Band hybridization significantly shifts the spectral weight of the Landau interactions from the conventional $s$-wave channel to unconventional non-$s$-wave channels, which results in anisotropic (nematic) Fermi surface distortions even with ordinary interactions in solids. The Ginzburg-Landau free energy is constructed by coupling the charge-nematic, spin-nematic, and ferromagnetic order parameters together, which shows that nematic electron states can be induced by metamagnetism. The connection between this mechanism and the anisotropic metamagnetc states observed in ${\text{Sr}}_{3}{\text{Ru}}_{2}{\text{O}}_{7}$ at high magnetic fields is studied in a multiband Hubbard model with the hybridized quasi-one-dimensional ${d}_{xz}$ and ${d}_{yz}$ bands.

First-order nature of a metamagnetic transition and mechanism of giant magnetoresistance in Mn2Sb0.95Sn0.05

Abstract: Magnetization behavior across a metamagnetic transition from an antiferromagnetic state to a ferrimagnetic state is investigated in detail for compound ${\mathrm{Mn}}_{2}{\mathrm{Sb}}_{0.95}{\mathrm{Sn}}_{0.05}$. The study clearly brings out various generic features associated with a first-order transition, viz., the appearance of hysteresis and the coexistence of magnetic phases. We also observe that the magnetization versus field butterfly loops occurs, while the virgin curve lies outside the envelope magnetization curve. The electronic specific-heat coefficient at low temperatures increases with increasing applied magnetic field, after the field is larger than the critical transition field. This is direct evidence of the formation of a super-zone gap that yields the change of density of electric states and further proves that the large magnetoresistance effect in intermetallic compounds is originated from the reconstruction of Fermi surface due to the collapse of the super-zone gap after the metamagnetic transition.