Itinerant-electron metamagnetism of the Hf1−xTaxFe2 (x=0.125 and 0.14) compounds under high pressure

Journal of Alloys and Compounds

Amara

et al. 2020

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With the use of neutron powder diffraction, we have discovered and characterized an extremely anisotropic thermal expansion, including negative thermal expansion (NTE), in an itinerant-electron system Hf0.86Ta0.14Fe2. It is revealed that the intermetallic compound Hf0.86Ta0.14Fe2 exhibits temperature-induced magnetic phase transitions from ferromagnetic (FM) to antiferromagnetic (AFM) order and then to the paramagnetic (PM) state upon heating. The FM-AFM transformation proceeds in a stepwise fashion, as a first-order phase transition, and is accompanied by an isomorphic (without change of symmetry) lattice collapse. The unit cell shrinks abruptly in the basal plane only, while it's dimension along the six-fold symmetry axis c changes continuously. The thermal evolution of the a lattice constant is found to drive the change from FM to AFM magnetic order. Hf0.86Ta0.14Fe2 shows a 0.41 % spontaneous volume reduction across the FM-AFM first-order magnetic transition, where a giant NTE, with a crystallographic volume thermal expansion coefficient -164×10 -6 K -1 , is observed. We further show that the AFM state can be transformed into a FM state by fewtesla magnetic fields, which results in a large positive magnetostriction. A remarkably large adiabatic temperature change of Tad = 2.2 K is obtained for a magnetic field change of 3 T around the FM-AFM transition temperature. Using angle dispersive synchrotron x-ray diffraction, the evolution of the lattice was investigated at room temperature under high pressures up to 25 GPa. The application of external pressure leads to the monotonous decrease of the unit-cell parameters. The contraction of the hexagonal lattice is anisotropic with a larger compression along the high-symmetry direction c. A bulk modulus of K0 = 223 GPa has been determined from the pressure-volume relationship.

Section: Introductionmentioning

confidence: 99%

Giant negative thermal expansion across the first-order magnetoelastic transition in Hf0.86Ta0.14Fe2

Diop

Journal of Alloys and Compounds

Amara

et al. 2020

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“…The FM-AFM transition has been explained by the IEM behavior of the Fe sublattice, monitored by the loss of ordered moment on a particular Fe site inducing an inversion of its Fe neighbour's moment orientation. The crystallographic origin of this FM-AFM transition is comparable to that of C14 hexagonal RFe2 compound (ScFe2 under pressure, (Hf,Ta)Fe2) 41,46,47 where the collapse of the Fe moment on the 2a site but not on the 6h site stabilizes the AFM structure at the expense of the FM one.…”

Section: Discussionmentioning

confidence: 65%

Influence of high pressure on the remarkable itinerant electron behavior in Y0.7Er0.3Fe2D4.2 compound

Arnold

Journal of Applied Physics

Paul‐Boncour

2023

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A monoclinic Y0.7Er0.3Fe2D4.2 compound exhibits unusual magnetic properties with different field induced magnetic transitions. The deuteride is ferrimagnetic at low temperature, and the Er and Fe sublattices present magnetic transitions at different temperatures. The Er moments are ordered below TEr = 55 K, whereas the Fe moments remain ferromagnetically coupled up to TM0 = 66 K. At TM0, the Fe moments display a sharp ferromagnetic–antiferromagnetic transition (FM–AFM) through itinerant electron metamagnetic behavior very sensitive to any volume change. Y0.7Er0.3Fe2D4.2 becomes paramagnetic above TN = 125 K. The pressure dependence of TEr and TM0 has been extracted from magnetic measurements under hydrostatic pressure up to 0.49 GPa. Both temperatures decrease linearly upon applied pressure with dTEr/dP = −126 and dTM0/dP = −140 K GPa−1 for a field of B = 0.03 T. Both magnetic Er and ferromagnetic Fe orders disappear at P = 0.44(4) GPa. However, under a larger applied field B = 5 T, dTM0/dP = −156 K GPa−1, whereas dTEr/dP = −134 K GPa−1 showing weaker sensitivity to pressure and magnetic field. At 2 K, the decrease of the saturation magnetization under pressure can be attributed to a reduction of the mean Er moment due to canting and/or a crystal field effect. Above TM0, the magnetization curves display metamagnetic behavior from an AFM to FM state, which is also very sensitive to the applied pressure. The transition field Btrans, which increases linearly upon heating, is shifted to a lower temperature upon applied pressure with ΔT = −17 K between 0 and 0.11 GPa. These results show strong decoupling of the Er and Fe magnetic sublattices vs temperature, applied field, and pressure.

“…A sharp first order ferromagnetic-antiferromagnetic transition (FM-AFM) observed at TFM-AFM = 131 K for YFe2H4.2 [56]. This transition displays the characteristics of an itinerant electron metamagnetic (IEM) behavior of the Fe sublattice as observed in hexagonal AFe2 compounds (A = Hf, Ta) [57][58][59][60][61]. A metamagnetic behavior is observed above TFM-AFM, with transition field increasing linearly versus temperature.…”

Section: Introductionmentioning

confidence: 77%

Origin of the metamagnetic transitions in Y1−Er Fe2(H,D)4.2 compounds

Paul‐Boncour

Journal of Magnetism and Magnetic Materials

Shtender

et al. 2020

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The structural and magnetic properties of Y1-xErxFe2 intermetallic compounds and their hydrides and deuterides Y1-xErxFe2H(D)4.2 have been investigated using X-ray diffraction and magnetic measurements under static and pulsed magnetic field up to 60 T. The intermetallics crystallize in the C15 cubic structure (Fd-3m space group), whereas corresponding hydrides and deuterides crystallize in a monoclinic structure (Pc space group). All compounds display a linear decrease of the unit cell volume versus Er concentration; the hydrides have a 0.8% larger cell volume compared to the deuterides with same Er content. They are ferrimagnetic at low field and temperature with a compensation point at x = 0.33 for the intermetallics and x = 0.57 for the hydrides and deuterides. A sharp first order ferromagnetic-antiferromagnetic (FM-AFM) transition is observed upon heating at TFM-AFM for both hydrides and deuterides. These compounds show two different types of field induced transitions, which have different physical origin. At low temperature (T < 50 K), a forced ferri-ferromagnetic metamagnetic transition with Btrans1  8 T, related to the change of the Er moments orientation from antiparallel to parallel Fe moment, is observed. Btrans1 is not sensitive to Er concentration, temperature and isotope effect. A second metamagnetic transition resulting from antiferromagnetic to ferrimagnetic state is also observed. The transition field Btrans2 increases linearly versus temperature and relates to the itinerant electron metamagnetic behavior of the Fe sublattice. An onset temperature TM0 is obtained by extrapolating TFM-AFM (B) at zero field. TM0 decreases linearly versus the Er content and is 45±5 K higher for the hydrides compared to the corresponding deuteride. The evolution of TM0 versus cell volume shows that it cannot be attributed exclusively to a pure volume effect and that electronic effects should also be considered.