Anisotropic magnetic properties and giant magnetocaloric effect in antiferromagnetic $R$MnO$_3$ crystals ($R$=Dy, Tb, Ho and Yb)

TL;DR

This study explores the anisotropic magnetic properties and giant magnetocaloric effects in $R$MnO$_3$ single crystals, revealing how magnetic transitions and entropy changes depend on field direction and material structure, with implications for low-temperature magnetic refrigeration.

Contribution

It provides a systematic analysis of the anisotropic magnetocaloric effects in $R$MnO$_3$ crystals, highlighting their potential for low-temperature magnetic cooling applications.

Findings

Significant anisotropic magnetic entropy change ($ riangle S_M$) observed.

Both inverse and normal magnetocaloric effects identified depending on field direction.

Large $ riangle S_M$ and cooling power suggest potential for magnetic refrigeration.

Abstract

We have systematically investigated the magnetic properties and magnetocaloric effect (MCE) in $R$MnO$_3$ ($R$$=$Dy, Tb, Ho and Yb) single crystals. Above a critical value of applied field ($H_c$), $R$MnO$_3$ undergo a first-order antiferromagnetic (AFM) to ferromagnetic (FM) transition below the ordering temperature ($T_{N}^{R}$) of $R^{3+}$ moment and a second-order FM to paramagnetic (PM) transition above $T_{N}^{R}$. Both $H$ and $T$ dependence of $M$ shows that the system is highly anisotropic in the FM as well as PM states and, as a result, the magnetic entropy change ($\Delta S_{M}$) is extremely sensitive to the direction of applied field and can be negative (normal MCE) or positive (inverse MCE). For hexagonal HoMnO$_3$ and YbMnO$_3$ systems, a very small inverse MCE is observed only for $H$ parallel to c axis and it decreases with increasing $H$ and crosses over to normal one above $H_c$. On the other hand, for orthorhombic DyMnO$_3$ and TbMnO$_3$, though the inverse MCE disappears above $H_c$ along easy-axis of magnetization, it increases rapidly with $H$ along hard-axis of magnetization for $T$$\ll$$T_{N}^{R}$. Except for YbMnO$_3$, the values of $\Delta S_{M}$, relative cooling power and adiabatic temperature change along easy-axis of magnetization are quite large in the field-induced FM state for a moderate field strength. The large values of these parameters, together with negligible hysteresis, suggest that the multiferroic manganites could be potential materials for magnetic refrigeration in the low-temperature region.