Magnetic field phase diagram of the non-cubic antiferromagnetic Mn5Si3

R. F. LUCCAS; A. CORREA-ORELLANA; F. J. MOMPEAN; M. GARCÍA- HERNANDEZ; S. VIEIRA; H. SUDEROW

Bariloche

Congreso; Advanced Topics in Magnetism and Superconductivity AToMS-2014; 2014

Transition metal magnets are characterized by having moments strongly linked to their local environment. This leads to a rich interplay between d-electron magnetism and nearest-neighbor interactions [1]. MnSi and MnGe crystallize in a cubic structure without center of inversion, leading to spiral magnetic order. The compound Mn5Si3 is antiferromagnetically ordered at low temperatures. Previous neutron scattering in polycrystalline orpowder samples show several magnetic phases, with two magnetic transitions T1N = 60 K and T2 N = 90 K. Below T1 N, spins are arranged in a non-collinear structure, showing local chirality.This phase is destroyed by a magnetic field of several Tesla, favoring the high temperature antiferromagnetic arrangement [2]. Here we have synthesized crystals of Mn5Si3 out of Cu flux. We obtain needles with typically 6 mm in length and cross section of about 1 mm2 with a non-regular octagonal section. We find, from magnetization measurements up to 7 T and down to 2 K performed on individual needles along their main axis, that there are actually three magnetic phases, with an additional transition at T1*N = 45 K. Contrary to results in other polycrystalline samples, we find that T1 N is magnetic field independent, whereas T1*N strongly decreases with the magnetic field, and presents transitions when increasing field at a fixed temperature. Our measurements suggest that the low temperature magnetic noncollinear structure unwinds with the magnetic field through metamagnetic transitions. There is an additional intermediate magnetic phase between 45 K and 60 K, which is probably also non-collinear. The role of sample synthesis on the magnetic structure is briefly discussed.