Abstract
We uncover high-order harmonics and the reverse of the squaring-up process, in terms of analyzing the evolution of magnetic orders in a centrosymmetric layered triangular-lattice magnet HoPdAl4鈦e2, based on a detailed study of the crystal structure, magnetic susceptibility, magnetization, heat capacity, and magnetic structure. Temperature dependencies of magnetic susceptibility and heat capacity show two magnetic transitions at 饾憞饾憗=10.5 K and 饾憞饾憽=5.5 K. Below 饾憞饾憗, Ho3+ spins order antiferromagnetically as a transverse spin-density wave with the propagation vector 饾拰1=(001.5鈭掟潧�) with 饾浛鈮�0.18. Upon further cooling through 饾憞饾憽, the high-order harmonics with 饾拰饾拸=(001.5鈭掟潙涒仮饾浛), 饾憶=3, 5, 7 develop, suggesting a squaring-up process. It is surprising that the squaring-up process does not continue down to 0 K but reverses the trend below 3 K. Magnetic-field-induced metastable transitions were observed in 饾憖鈦�(饾惢) curves with the fields applied both parallel and perpendicular to the triangular-lattice plane. Neutron-diffraction results suggest that the magnetization process in HoPdAl4鈦e2 involves the conversion of 饾拰饾拸=(001.5鈭掟潙涒仮饾浛) with 饾憶=1, 3, 5, 7, to a ferromagnetic 饾拰饾懎=(000) component. It is worth noting that the already weak seventh harmonic magnetic peak is enhanced by applying a small magnetic field in the 饾憥鈦潙� plane at 1.5 K or warming up to 3 K, accompanied by a slight decrease of 饾浛.
