Strain-modulated helimagnetism and emergent magnetic phase diagrams in highly crystalline MnP nanorod films

TL;DR

This study investigates how strain influences helimagnetism in MnP nanorod films, revealing strain-induced magnetic phase transitions and complex phase diagrams not present in bulk crystals, with potential implications for magnetic device applications.

Contribution

It provides the first detailed magnetic phase diagrams of strained MnP nanorod films, highlighting emergent magnetic phases driven by strain and dimensionality effects.

Findings

Strain raises the helimagnetic transition temperature compared to single crystals.

Identification of multiple helical magnetic phases and their evolution with temperature and field.

Construction of comprehensive magnetic phase diagrams for the nanorod films.

Abstract

We explore strain-modulated helimagnetism in highly crystalline MnP nanorod films grown on Si(100) substrates using molecular beam epitaxy. The strained MnP film exhibits a paramagnetic to ferromagnetic (PM-FM) phase transition at TC ~ 279 K, and the FM to helical phase transition at TN ~ 110 K. The value of TN is greater than TN ~ 47 K for the MnP single crystal, indicating strong strain-modulated helimagnetic states in the MnP nanorod film. The presence of significant thermal hysteresis in the helical phase indicates coexistence of competing magnetic interactions, leading to the first-order metamagnetic transition. Similar to its single crystal counterpart, an anisotropic magnetic effect is observed in the MnP film, which is independently confirmed by magnetic hysteresis loop and radio-frequency transverse susceptibility (TS) measurements. The evolution of screw (SCR) to CONE and FAN phase is precisely tracked from magnetization versus magnetic field/temperature measurements. The temperature dependence of the anisotropy fields, extracted from the TS spectra, yields further insight into the competing nature of the magnetic phases. Unfolding of the different helical phases at T < 120 K (~TN) is analyzed by the temperature- and field-dependent magnetic entropy change. Based on these findings, the comprehensive magnetic phase diagrams of the MnP nanorod film are constructed for the first time for both the in-plane and out-of-plane magnetic field directions, revealing emergent strain/dimensionality-driven helical magnetic features that are absent in the magnetic phase diagram of the MnP single crystal.