Structural, Magnetic, and Cryogenic Magnetocaloric Properties of Xenotime-Type YbPO ₄

The polycrystalline sample of YbPO 4 was synthesized using a conventional solid-state reaction technique. Rietveld refinement of X-ray diffraction data confirms that the compound crystallizes in a single-phase tetragonal structure (xenotime-type, space group I4 1 /amd). Microstructural analysis reveals micrometric grains (~1.2 μm) composed of nanometric subdomains (~100 nm), indicating a hierarchical grain structure. Magnetic measurements indicate predominant antiferromagnetic interactions, as evidenced by a negative Curie–Weiss temperature (θ p = -20.73 K). The magnetocaloric properties were investigated over an applied magnetic field range of 0–50 kOe. A significant magnetic entropy change is observed, reaching (– ΔS M max ) ≈ 12 J·kg -1 ·K -1 at 2 K. The relative cooling power (RCP) is estimated to be approximately 140 J·kg -1 . The adiabatic temperature change (ΔT ad ), derived from heat capacity and magnetic entropy data, reaches maximum values of 4.6 K for ΔH = 0-20 kOe and 11.9 K for ΔH = 0-50 kOe at approximately 2 K. The continuous magnetic response and absence of thermal hysteresis suggest a second-order magnetic transition occurring below the investigated temperature range. These results indicate that YbPO 4 exhibits a measurable cryogenic magnetocaloric response, providing useful insights into low-temperature magnetocaloric behavior in rare-earth phosphates.