Spin-reorientation phase transition and induced spin reversals in NdFeO3 : Theory and experiment

Spin-reorientation (SR) phase transition (PT), spin reversals, hysteresis, and thermal phenomena in neodymium orthoferrite are studied within the framework of the previously presented model of the magnetic properties of orthoferrites []. A rigorous proof of an appearance of the SR second-order PT at temperature <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>T</a:mi><a:mi>SR</a:mi></a:msub></a:math> in infinitesimal magnetic field along one of the crystal symmetry axes is given. It is done without introduction of high-order anisotropy constants used in traditional phenomenological theories for the orthoferrite thermodynamics. The expression for temperature <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:msub><b:mi>T</b:mi><b:mi>SR</b:mi></b:msub></b:math> considers a complex competition of existing anisotropies. Unfortunately, due to the displacement of domain boundaries, this temperature is quite difficult to determine. Since the anisotropy at temperature <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:msub><c:mi>T</c:mi><c:mi>SR</c:mi></c:msub></c:math> is predicted to disappear, a method for <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:msub><d:mi>T</d:mi><d:mi>SR</d:mi></d:msub></d:math> determination is proposed. Particular attention is paid to the study of an influence of demagnetizing field on the structure of phase diagrams as well as to the analysis of the experimental data on temperature and field dependence of the magnetization. It has been established that the specimen shape essentially influences temperature dependences of the PT critical fields. Using the experimental temperature dependence of the spin-reversal critical fields, the microscopic anisotropic interaction parameters in neodymium orthoferrite are determined, on the basis of which the magnetization, spin-reversal energies, specific heat capacity, and hysteresis loops are calculated. The results of the experiment and theory are in good agreement. Published by the American Physical Society 2024